Adopting agency | BSC | BSC-CG | SFM | HCD | DSA | OSHPD | BSCC | DPH | AGR | DWR | CEC | CA | SL | |||||||||
1 | 2 | 1/AC | AC | SS | SS/CC | 1 | 1R | 2 | 3 | 4 | 5 | |||||||||||
Adopt entire chapter | X | |||||||||||||||||||||
Adopt entire chapter as amended (amended sections listed below) | X | X | X | X | X | |||||||||||||||||
Adopt only those sections that are listed below | ||||||||||||||||||||||
Chapter / Section | ||||||||||||||||||||||
1801.1.1 — 1801.1.3 | X | X | X | |||||||||||||||||||
1802.1 | X | |||||||||||||||||||||
1803.1 | X | X | X | |||||||||||||||||||
1803.1.1 —1803.1.1.5 | X | |||||||||||||||||||||
1803.2 | X | |||||||||||||||||||||
1803.3.1 | X | X | X | |||||||||||||||||||
1803.3.5.4 Exception |
X | X | X | |||||||||||||||||||
1803.6 | X | X | X | |||||||||||||||||||
1803.7 | X | X | X | |||||||||||||||||||
1804.4.1 | X | |||||||||||||||||||||
1805.2 | X | X | X | |||||||||||||||||||
1805.4.1, Exception 2 |
X | |||||||||||||||||||||
1805.4.3 | ||||||||||||||||||||||
1807.1.3 | X | X | X | |||||||||||||||||||
1807.1.4 | X | X | X | |||||||||||||||||||
1807.1.5, Exception |
X | X | X | |||||||||||||||||||
1807.1.6 | X | X | X | |||||||||||||||||||
1807.2 | X | X | X | |||||||||||||||||||
1807.2.2 | X | X | X | |||||||||||||||||||
1807.2.4 | X | X | X | |||||||||||||||||||
1808.8 Exception |
X | X | X | |||||||||||||||||||
Table 1808.8.1 | X | X | X | |||||||||||||||||||
1808.8.6 | X | X | X | |||||||||||||||||||
1809.3 | X | X | X | |||||||||||||||||||
1809.7 | X | X | X | |||||||||||||||||||
1809.8 | X | X | X | |||||||||||||||||||
1809.9 | X | X | X | |||||||||||||||||||
1809.12 | X | X | X | |||||||||||||||||||
1809.14 | X | X | X | |||||||||||||||||||
1810.3.1.5.1 | X | X | X | |||||||||||||||||||
1810.3.2.4 | X | X | X | |||||||||||||||||||
1810.3.5.3.3 | X | X | X | |||||||||||||||||||
1810.3.8.3.3 Exception |
X | X | X | |||||||||||||||||||
1810.3.8.3.4 Exception |
X | X | X | |||||||||||||||||||
1810.3.9.4.2.1 | X | X | X | |||||||||||||||||||
1810.3.10.4 | X | X | ||||||||||||||||||||
1810.3.10.4.1 | X | X | X | |||||||||||||||||||
1810.3.11 | X | X | X | |||||||||||||||||||
1810.4.1.5 | X | X | X | |||||||||||||||||||
1811 | X | X | X | |||||||||||||||||||
1812 | X | X | X | |||||||||||||||||||
1813 | X | X | X |
- The state agency does not adopt sections identified with the following symbol: †
- The Office of the State Fire Marshal's adoption of this chapter or individual sections is applicable to structures regulated by other state agencies pursuant to Section 1.11.
Requirements governing grading and earthwork construction, including excavation and fills, are set forth in Division 70, Article 1, Chapter IX of the LAMC.
Hillside buildings (buildings constructed on slopes steeper than 1 unit vertical in 3 units horizontal [33.3%] slope) shall comply with LAMC Subsection 91.1613.9 (seismic design provisions for hillside buildings) and this division.
[HCD 1] For limited-density owner-built rural dwellings, pier foundations, stone masonry footings and foundations, pressure-treated lumber, poles or equivalent foundation materials or designs may be used, provided that the bearing is sufficient for the purpose intended.
The preliminary soil report may be waived if the building department of the city, county, or city and county, or other enforcement agency charged with the administration and enforcement of the provisions of Section 1803.1.1, shall determine that, due to the knowledge such department has as to the soil qualities of the soil of the subdivision or lot, no preliminary analysis is necessary.
The soil investigation shall be prepared by a civil engineer who is registered in this state. It shall recommend corrective action which is likely to prevent structural damage to each dwelling proposed to be constructed on the expansive soil.
Geotechnical investigations shall be conducted in accordance with Sections 1803.3 through 1803.5.
Exception: The building official shall be permitted to waive the requirement for a geotechnical investigation where satisfactory data from adjacent areas is available that demonstrates an investigation is not necessary for any of the conditions in Sections 1803.5.1 through 1803.5.6 and Sections 1803.5.10 and 1803.5.11.
[OSHPD 2] Geotechnical reports are not required for one-story, wood-frame and light-steel-frame buildings of Type V construction and 4,000 square feet (371 m2) or less in floor area, not located within Earthquake Fault Zones or Seismic Hazard Zones as shown in the most recently published maps from the California Geological Survey (CGS). Allowable foundation and lateral soil pressure values may be determined from Table 1806.2.
[OSHPD 1R, 2 & 5] There shall not be less than one boring or exploration shaft for each 5,000 square feet (465 m2) of building area at the foundation level with a minimum of two provided for any one building. A boring may be considered to reflect subsurface conditions relevant to more than one building, subject to the approval of the enforcement agency.
Borings shall be of sufficient size to permit visual examination of the soil in place or, in lieu thereof, cores shall be taken.
Borings shall be of sufficient depth and size to adequately characterize subsurface conditions.
Exception: Single-story Type V skilled nursing or intermediate care facilities utilizing wood-frame or light-steel frame construction.
In areas likely to have expansive soil, the building official shall require soil tests to determine where such soils do exist.
Soils meeting all four of the following provisions shall be considered to be expansive, except that tests to show compliance with Items 1, 2 and 3 shall not be required if the test prescribed in Item 4 is conducted:
- Plasticity index (PI) of 15 or greater, determined in accordance with ASTM D4318.
- More than 10 percent of the soil particles pass a No. 200 sieve (75 µm), determined in accordance with ASTM D422.
- More than 10 percent of the soil particles are less than 5 micrometers in size, determined in accordance with ASTM D422.
- Expansion index greater than 20, determined in accordance with ASTM D4829.
A subsurface soil investigation shall be performed to determine whether the existing ground water table is above or within 5 feet (1524 mm) below the elevation of the lowest floor level where such floor is located below the finished ground level adjacent to the foundation.
Exception: [OSHPD 1R, 2 & 5] Not permitted by OSHPD. A subsurface soil investigation to determine the location of the ground water table shall not be required where waterproofing is provided in accordance with Section 1805.
Where deep foundations will be used, a geotechnical investigation shall be conducted and shall include all of the following, unless sufficient data on which to base the design and installation is otherwise available:
- Recommended deep foundation types and installed capacities.
- Recommended center-to-center spacing of deep foundation elements.
- Driving criteria.
- Installation procedures.
- Field inspection and reporting procedures (to include procedures for verification of the installed bearing capacity where required).
- Load test requirements.
- Suitability of deep foundation materials for the intended environment.
- Designation of bearing stratum or strata.
- Reductions for group action, where necessary.
Where shallow foundations will bear on compacted fill material more than 12 inches (305 mm) in depth, a geotechnical investigation shall be conducted and shall include all of the following:
- Specifications for the preparation of the site prior to placement of compacted fill material.
- Specifications for material to be used as compacted fill.
- Test methods to be used to determine the maximum dry density and optimum moisture content of the material to be used as compacted fill.
- Maximum allowable thickness of each lift of compacted fill material.
- Field test method for determining the in-place dry density of the compacted fill.
- Minimum acceptable in-place dry density expressed as a percentage of the maximum dry density determined in accordance with Item 3.
- Number and frequency of field tests required to determine compliance with Item 6.
Where shallow foundations will bear on controlled low-strength material (CLSM), a geotechnical investigation shall be conducted and shall include all of the following:
- Specifications for the preparation of the site prior to placement of the CLSM.
- Specifications for the CLSM.
- Laboratory or field test method(s) to be used to determine the compressive strength or bearing capacity of the CLSM.
- Test methods for determining the acceptance of the CLSM in the field.
- Number and frequency of field tests required to determine compliance with Item 4.
For structures assigned to Seismic Design Category C, D, E or F, a geotechnical investigation shall be conducted, and shall include an evaluation of all of the following potential geologic and seismic hazards:
- Slope instability.
- Liquefaction.
- Total and differential settlement.
- Surface displacement due to faulting or seismically induced lateral spreading or lateral flow.
For structures assigned to Seismic Design Category D, E or F, the geotechnical investigation required by Section 1803.5.11 shall include all of the following as applicable:
- The determination of dynamic seismic lateral earth pressures on foundation walls and retaining walls supporting more than 6 feet (1.83 m) of backfill height due to design earthquake ground motions.
The potential for liquefaction and soil strength loss evaluated for site peak ground acceleration, earthquake magnitude and source characteristics consistent with the maximum considered earthquake ground motions. Peak ground acceleration shall be determined based on one of the following:
- 2.1. A site-specific study in accordance with Chapter 21 of ASCE 7.
- 2.2. In accordance with Section 11.8.3 of ASCE 7.
An assessment of potential consequences of liquefaction and soil strength loss including, but not limited to, the following:
- 3.1. Estimation of total and differential settlement.
- 3.2. Lateral soil movement.
- 3.3. Lateral soil loads on foundations.
- 3.4. Reduction in foundation soil-bearing capacity and lateral soil reaction.
- 3.5. Soil downdrag and reduction in axial and lateral soil reaction for pile foundations.
- 3.6. Increases in soil lateral pressures on retaining walls.
- 3.7. Flotation of buried structures.
Discussion of mitigation measures such as, but not limited to, the following:
- 4.1. Selection of appropriate foundation type and depths.
- 4.2. Selection of appropriate structural systems to accommodate anticipated displacements and forces.
- 4.3. Ground stabilization.
- 4.4. Any combination of these measures and how they shall be considered in the design of the structure.
Where geotechnical investigations are required, a written report of the investigations shall be submitted to the building official by the permit applicant at the time of permit application. This geotechnical report shall include, but need not be limited to, the following information:
- A plot showing the location of the soil investigations.
- A complete record of the soil boring and penetration test logs and soil samples.
- A record of the soil profile.
- Elevation of the water table, if encountered.
- Recommendations for foundation type and design criteria, including but not limited to: bearing capacity of natural or compacted soil; provisions to mitigate the effects of expansive soils; mitigation of the effects of liquefaction, differential settlement and varying soil strength; and the effects of adjacent loads.
- Expected total and differential settlement.
- Deep foundation information in accordance with Section 1803.5.5.
- Special design and construction provisions for foundations of structures founded on expansive soils, as necessary.
- Compacted fill material properties and testing in accordance with Section 1803.5.8.
- Controlled low-strength material properties and testing in accordance with Section 1803.5.9.
- [OSHPD 1R, 2 & 5] The report shall consider the effects of seismic hazard in accordance with Section 1803.7.
- Reports are not required for one-story, wood-frame and light-steel-frame buildings of Type V skilled nursing or intermediate care facilities construction and 4,000 square feet (371 m2) or less in floor area, not located within Earthquake Fault Zones or Seismic Hazard Zones as shown in the most recently published maps from the California Geological Survey (CGS); nonstructural, associated structural or voluntary structural alterations and incidental structural additions or alterations, and structural repairs for other than earthquake damage.
- A previous report for a specific site may be resubmitted, provided that a reevaluation is made and the report is found to be currently appropriate.
The purpose of the geohazard report shall be to identify geologic and seismic conditions that may require project mitigations. The reports shall contain data which provide an assessment of the nature of the site and potential for earthquake damage based on appropriate investigations of the regional and site geology, project foundation conditions and the potential seismic shaking at the site. The report shall be prepared by a California-certified engineering geologist in consultation with a California-registered geotechnical engineer.
The preparation of the geohazard report shall consider the most recent CGS Note 48; Checklist for the Review of Engineering Geology and Seismology Reports for California Public School, Hospitals, and Essential Services Buildings. In addition, the most recent version of CGS Special Publication 42, Fault Rupture Hazard Zones in California, shall be considered for project sites proposed within an Alquist-Priolo Earthquake Fault Zone. The most recent version of CGS Special Publication 117, Guidelines for Evaluating and Mitigating Seismic Hazards in California, shall be considered for project sites proposed within a Seismic Hazard Zone. All conclusions shall be fully supported by satisfactory data and analysis.
In addition to requirements in Sections 1803.5.11 and 1803.5.12, the report shall include, but shall not be limited to, the following:
- Site geology.
- Evaluation of the known active and potentially active faults, both regional and local.
- Ground-motion parameters, as required by Section 1613 and ASCE 7.
The excavation outside the foundation shall be backfilled with soil that is free of organic material, construction debris, cobbles and boulders or with a controlled low-strength material (CLSM). The backfill shall be placed in lifts and compacted in a manner that does not damage the foundation or the waterproofing or dampproofing material.
Exception: CLSM need not be compacted.
The ground immediately adjacent to the foundation shall be sloped away from the building at a slope of not less than one unit vertical in 20 units horizontal (5-percent slope) for a minimum distance of 10 feet (3048 mm) measured perpendicular to the face of the wall. If physical obstructions or lot lines prohibit 10 feet (3048 mm) of horizontal distance, a 5-percent slope shall be provided to an approved alternative method of diverting water away from the foundation. Swales used for this purpose shall be sloped not less than 2 percent where located within 10 feet (3048 mm) of the building foundation. Impervious surfaces within 10 feet (3048 mm) of the building foundation shall be sloped not less than 2 percent away from the building.
Exceptions:
- Where climatic or soil conditions warrant, the slope of the ground away from the building foundation shall be permitted to be reduced to not less than one unit vertical in 48 units horizontal (2-percent slope).
- Impervious surfaces shall be permitted to be sloped less than 2 percent where the surface is a door landing or ramp that is required to comply with Section 1010.1.5, 1012.3 or 1012.6.1.
The procedure used to establish the final ground level adjacent to the foundation shall account for additional settlement of the backfill.
In flood hazard areas established in Section 1612.3, grading, fill, or both, shall not be approved:
- Unless such fill is placed, compacted and sloped to minimize shifting, slumping and erosion during the rise and fall of flood water and, as applicable, wave action.
- In floodways, unless it has been demonstrated through hydrologic and hydraulic analyses performed by a registered design professional in accordance with standard engineering practice that the proposed grading or fill, or both, will not result in any increase in flood levels during the occurrence of the design flood.
- In coastal high hazard areas, unless such fill is conducted or placed to avoid diversion of water and waves toward any building or structure.
- Where design flood elevations are specified but floodways have not been designated, unless it has been demonstrated that the cumulative effect of the proposed flood hazard area encroachment, when combined with all other existing and anticipated flood hazard area encroachment, will not increase the design flood elevation more than 1 foot (305 mm) at any point.
Where shallow foundations will bear on compacted fill material, the compacted fill shall comply with the provisions of an approved geotechnical report, as set forth in Section 1803.
Exception: Compacted fill material 12 inches (305 mm) in depth or less need not comply with an approved report, provided that the in-place dry density is not less than 90 percent of the maximum dry density at optimum moisture content determined in accordance with ASTM D1557. The compaction shall be verified by special inspection in accordance with Section 1705.6.
Walls or portions thereof that retain earth and enclose interior spaces and floors below grade shall be waterproofed and dampproofed in accordance with this section, with the exception of those spaces containing groups other than residential and institutional where such omission is not detrimental to the building or occupancy.
Ventilation for crawl spaces shall comply with Section 1203.4.
For buildings and structures in flood hazard areas as established in Section 1612.3, the finished ground level of an under-floor space such as a crawl space shall be equal to or higher than the outside finished ground level on one side or more.
Exception: Under-floor spaces of Group R-3 buildings that meet the requirements of FEMA TB 11.
Dampproofing materials for floors shall be installed between the floor and the base course required by Section 1805.4.1, except where a separate floor is provided above a concrete slab.
Where installed beneath the slab, dampproofing shall consist of not less than 6-mil (0.006 inch; 0.152 mm) polyethylene with joints lapped not less than 6 inches (152 mm), or other approved methods or materials. Where permitted to be installed on top of the slab, dampproofing shall consist of mopped-on bitumen, not less than 4-mil (0.004 inch; 0.102 mm) polyethylene, or other approved methods or materials. Joints in the membrane shall be lapped and sealed in accordance with the manufacturer's installation instructions.
Dampproofing materials for walls shall be installed on the exterior surface of the wall, and shall extend from the top of the footing to above ground level.
Dampproofing shall consist of a bituminous material, 3 pounds per square yard (16 N/m2) of acrylic modified cement, 1/8 inch (3.2 mm) coat of surface-bonding mortar complying with ASTM C887, any of the materials permitted for waterproofing by Section 1805.3.2 or other approved methods or materials.
Prior to application of dampproofing materials on concrete walls, holes and recesses resulting from the removal of form ties shall be sealed with a bituminous material or other approved methods or materials. Unit masonry walls shall be parged on the exterior surface below ground level with not less than 3/8 inch (9.5 mm) of Portland cement mortar. The parging shall be coved at the footing.
Exception: Parging of unit masonry walls is not required where a material is approved for direct application to the masonry.
Floors required to be waterproofed shall be of concrete and designed and constructed to withstand the hydrostatic pressures to which the floors will be subjected.
Waterproofing shall be accomplished by placing a membrane of rubberized asphalt, butyl rubber, fully adhered/fully bonded HDPE or polyolefin composite membrane or not less than 6-mil [0.006 inch (0.152 mm)] polyvinyl chloride with joints lapped not less than 6 inches (152 mm) or other approved materials under the slab. Joints in the membrane shall be lapped and sealed in accordance with the manufacturer's installation instructions.
Walls required to be waterproofed shall be of concrete or masonry and shall be designed and constructed to withstand the hydrostatic pressures and other lateral loads to which the walls will be subjected.
Waterproofing shall be applied from the bottom of the wall to not less than 12 inches (305 mm) above the maximum elevation of the ground water table. The remainder of the wall shall be dampproofed in accordance with Section 1805.2.2. Waterproofing shall consist of two-ply hot-mopped felts, not less than 6-mil (0.006 inch; 0.152 mm) polyvinyl chloride, 40-mil (0.040 inch; 1.02 mm) polymer-modified asphalt, 6-mil (0.006 inch; 0.152 mm) polyethylene or other approved methods or materials capable of bridging nonstructural cracks. Joints in the membrane shall be lapped and sealed in accordance with the manufacturer's installation instructions.
Floors of basements, except as provided for in Section 1805.1.1, shall be placed over a floor base course not less than 4 inches (102 mm) in thickness that consists of gravel or crushed stone containing not more than 10 percent of material that passes through a No. 4 (4.75 mm) sieve.
Presumptive load-bearing values shall apply to materials with similar physical characteristics and dispositions.
Mud, organic silt, organic clays, peat or unprepared uncertified fill shall not be assumed to have a presumptive load-bearing capacity unless data to substantiate the use of such a value are submitted.
CLASS OF MATERIALS | VERTICAL FOUNDATION PRESSURE (psf) |
LATERAL BEARING PRESSURE (psf/ft below natural grade) |
LATERAL SLIDING RESISTANCE | |
Coefficient of frictiona | Cohesion (psf)b | |||
1. Crystalline bedrock | 12,000 | 1,200 | 0.70 | — |
2. Sedimentary and foliated rock | 4,000 | 400 | 0.35 | — |
3. Sandy gravel and gravel (GW and GP) | 3,000 | 200 | 0.35 | — |
4. Sand, silty sand, clayey sand, silty gravel and clayey gravel (SW, SP, SM, SC, GM and GC) | 2,000 | 150 | 0.25 | — |
5. Clay, sandy clay, silty clay, clayey silt, silt and sandy silt (CL, ML, MH and CH) | 1,500 | 100 | — | 130 |
- Coefficient to be multiplied by the dead load.
- Cohesion value to be multiplied by the contact area, as limited by Section 1806.3.2.
Concrete and masonry foundation walls shall be designed in accordance with Chapter 19 or 21, as applicable.
Exception: [OSHPD 1R, 2 & 5] Not permitted by OSHPD. Concrete and masonry foundation walls shall be permitted to be designed and constructed in accordance with Section 1807.1.6.
Concrete foundation walls shall comply with the following:
- The thickness shall comply with the requirements of Table 1807.1.6.2.
- The size and spacing of vertical reinforcement shown in Table 1807.1.6.2 are based on the use of reinforcement with a minimum yield strength of 60,000 pounds per square inch (psi) (414 MPa). Vertical reinforcement with a minimum yield strength of 40,000 psi (276 MPa) or 50,000 psi (345 MPa) shall be permitted, provided that the same size bar is used and the spacing shown in the table is reduced by multiplying the spacing by 0.67 or 0.83, respectively.
- Vertical reinforcement, where required, shall be placed nearest the inside face of the wall a distance, d, from the outside face (soil face) of the wall. The distance, d, is equal to the wall thickness, t, minus 1.25 inches (32 mm) plus one-half the bar diameter, db, [d = t - (1.25 + db / 2)]. The reinforcement shall be placed within a tolerance of ± 3/8 inch (9.5 mm) where d is less than or equal to 8 inches (203 mm) or ± 1/2 inch (12.7 mm) where d is greater than 8 inches (203 mm).
- In lieu of the reinforcement shown in Table 1807.1.6.2, smaller reinforcing bar sizes with closer spacings that provide an equivalent cross-sectional area of reinforcement per unit length shall be permitted.
- Concrete cover for reinforcement measured from the inside face of the wall shall be not less than 3/4 inch (19.1 mm). Concrete cover for reinforcement measured from the outside face of the wall shall be not less than 11/2 inches (38 mm) for No. 5 bars and smaller, and not less than 2 inches (51 mm) for larger bars.
- Concrete shall have a specified compressive strength, f 'c, of not less than 2,500 psi (17.2 MPa).
- The unfactored axial load per linear foot of wall shall not exceed 1.2 t f 'c where t is the specified wall thickness in inches.
TABLE 1807.1.6.2
CONCRETE FOUNDATION WALLSb, c
MAXIMUM
HEIGHT
(feet)
|
MAXIMUM
UNBALANCED
BACKFILL
HEIGHTe (feet)
|
MINIMUM VERTICAL REINFORCEMENT-BAR SIZE AND SPACING (inches) | ||||||||
Design lateral soil loada (psf per foot of depth) | ||||||||||
30d | 45d | 60 | ||||||||
Minimum wall thickness (inches) | ||||||||||
7.5 | 9.5 | 11.5 | 7.5 | 9.5 | 11.5 | 7.5 | 9.5 | 11.5 | ||
5 | 4 | PC | PC | PC | PC | PC | PC | PC | PC | PC |
5
|
PC |
PC
|
PC
|
PC
|
PC
|
PC
|
PC
|
PC
|
PC
|
|
6 | 4 | PC |
PC
|
PC
|
PC
|
PC
|
PC
|
PC
|
PC
|
PC
|
5
|
PC |
PC
|
PC
|
PC
|
PC
|
PC
|
PC
|
PC
|
PC
|
|
6 | PC |
PC
|
PC
|
PC
|
PC
|
PC
|
PC
|
PC
|
PC
|
|
7 | 4 | PC |
PC
|
PC
|
PC
|
PC
|
PC
|
PC
|
PC
|
PC
|
5
|
PC |
PC
|
PC
|
PC
|
PC
|
PC
|
PC
|
PC
|
PC
|
|
6 | PC |
PC
|
PC
|
PC
|
PC
|
PC
|
#5 at 48
|
PC
|
PC
|
|
7 | PC |
PC
|
PC
|
#5 at 46 |
PC
|
PC
|
#6 at 48 | PC | PC | |
8 | 4 | PC |
PC
|
PC
|
PC
|
PC
|
PC
|
PC
|
PC
|
PC
|
5
|
PC |
PC
|
PC
|
PC
|
PC
|
PC
|
PC
|
PC
|
PC
|
|
6 | PC |
PC
|
PC
|
PC
|
PC
|
PC
|
#5 at 43
|
PC
|
PC
|
|
7 | PC |
PC
|
PC
|
#5 at 41 |
PC
|
PC
|
#6 at 43 | PC | PC | |
8 | #5 at 47 | PC | PC | #6 at 43 | PC | PC | #6 at 32 | #6 at 44 | PC | |
9 | 4 | PC |
PC
|
PC
|
PC
|
PC
|
PC
|
PC
|
PC
|
PC
|
5
|
PC |
PC
|
PC
|
PC
|
PC
|
PC
|
PC
|
PC
|
PC
|
|
6 | PC |
PC
|
PC
|
PC
|
PC
|
PC
|
#5 at 39
|
PC
|
PC
|
|
7 | PC |
PC
|
PC
|
#5 at 37 |
PC
|
PC
|
#6 at 38 | #5 at 37 | PC | |
8 | #5 at 41 | PC | PC | #6 at 38 | #5 at 37 | PC | #7 at 39 | #6 at 39 | #4 at 48 | |
9d
|
#6 at 46
|
PC
|
PC
|
#7 at 41
|
#6 at 41
|
PC
|
#7 at 31
|
#7 at 41 | #6 at 39 | |
10 | 4 | PC |
PC
|
PC
|
PC
|
PC
|
PC
|
PC
|
PC
|
PC
|
5
|
PC |
PC
|
PC
|
PC
|
PC
|
PC
|
PC
|
PC
|
PC
|
|
6 | PC |
PC
|
PC
|
PC
|
PC
|
PC
|
#5 at 37
|
PC
|
PC
|
|
7 | PC |
PC
|
PC
|
#6 at 48 |
PC
|
PC
|
#6 at 35 | #6 at 48 | PC | |
8 | #5 at 38 | PC | PC | #7 at 47 | #6 at 47 | PC | #7 at 35 | #7 at 47 | #6 at 45 | |
9d
|
#6 at 41
|
#4 at 48
|
PC
|
#7 at 37
|
#7 at 48
|
#4 at 48
|
#6 at 22
|
#7 at 37 | #7 at 47 | |
10d | #7 at 45 | #6 at 45 | PC | #7 at 31 | #7 at 40 | #6 at 38 | #6 at 22 | #7 at 30 | #7 at 38 |
For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 pound per square foot per foot = 0.157 kPa/m.
- For design lateral soil loads, see Section 1610.
- Provisions for this table are based on design and construction requirements specified in Section 1807.1.6.2.
- PC = Plain Concrete.
- Where unbalanced backfill height exceeds 8 feet and design lateral soil loads from Table 1610.1 are used, the requirements for 30 and 45 psf per foot of depth are not applicable (see Section 1610 ).
- For height of unbalanced backfill, see Section 1807.1.2.
Based on the seismic design category assigned to the structure in accordance with Section 1613, concrete foundation walls designed using Table 1807.1.6.2 shall be subject to the following limitations:
- Seismic Design Categories A and B. Not less than one No. 5 bar shall be provided around window, door and similar sized openings. The bar shall be anchored to develop fy in tension at the corners of openings.
- Seismic Design Categories C, D, E and F. Tables shall not be used except as allowed for plain concrete members in Section 1905.1.7.
Masonry foundation walls shall comply with the following:
- The thickness shall comply with the requirements of Table 1807.1.6.3(1) for plain masonry walls or Table 1807.1.6.3(2), 1807.1.6.3(3) or 1807.1.6.3(4) for masonry walls with reinforcement.
- Vertical reinforcement shall have a minimum yield strength of 60,000 psi (414 MPa).
- The specified location of the reinforcement shall equal or exceed the effective depth distance, d, noted in Tables 1807.1.6.3(2), 1807.1.6.3(3) and 1807.1.6.3(4) and shall be measured from the face of the exterior (soil) side of the wall to the center of the vertical reinforcement. The reinforcement shall be placed within the tolerances specified in TMS 602, Article 3.4.B.11, of the specified location.
- Grout shall comply with Section 2103.3.
- Concrete masonry units shall comply with ASTM C90.
- Clay masonry units shall comply with ASTM C652 for hollow brick, except compliance with ASTM C62 or ASTM C216 shall be permitted where solid masonry units are installed in accordance with Table 1807.1.6.3(1) for plain masonry.
- Masonry units shall be laid in running bond and installed with Type M or S mortar in accordance with Section 2103.2.1.
- The unfactored axial load per linear foot of wall shall not exceed 1.2 t f 'm where t is the specified wall thickness in inches and f 'm is the specified compressive strength of masonry in pounds per square inch.
- Not less than 4 inches (102 mm) of solid masonry shall be provided at girder supports at the top of hollow masonry unit foundation walls.
- Corbeling of masonry shall be in accordance with Section 2104.1. Where an 8-inch (203 mm) wall is corbeled, the top corbel shall not extend higher than the bottom of the floor framing and shall be a full course of headers not less than 6 inches (152 mm) in length or the top course bed joint shall be tied to the vertical wall projection. The tie shall be W2.8 (4.8 mm) and spaced at a maximum horizontal distance of 36 inches (914 mm). The hollow space behind the corbelled masonry shall be filled with mortar or grout.
TABLE 1807.1.6.3(1)
PLAIN MASONRY FOUNDATION WALLSa, b, c
MAXIMUM WALL HEIGHT (feet) | MAXIMUM UNBALANCED BACKFILL HEIGHTe (feet) | MINIMUM NOMINAL WALL THICKNESS (inches) | ||
Design lateral soil loada (psf per foot of depth) | ||||
30f | 45f | 60 | ||
7 | 4 (or less) | 8 | 8 | 8 |
5 | 8 | 10 | 10 | |
6 | 10 | 12 | 10 (solidc) | |
7
|
12
|
10 (solidc)
|
10 (solidc)
|
|
8 | 4 (or less) | 8 | 8 | 8 |
5 | 8 | 10 | 10 | |
6 | 10 | 12 | 12 (solidc) | |
7
|
12
|
12 (solidc)
|
Note d
|
|
8 | 10 (solidc) | 12 (solidc) | Note d | |
9 | 4 (or less) | 8 | 8 | 8 |
5 | 8 | 10 | 12 | |
6 | 12 | 12 | 12 (solidc) | |
7
|
12 (solidc)
|
12 (solidc)
|
Note d
|
|
8 | 12 (solidc) | Note d | Note d | |
9f
|
Note d | Note d | Note d |
For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 pound per square foot per foot = 0.157 kPa/m.
- For design lateral soil loads, see Section 1610.
- Provisions for this table are based on design and construction requirements specified in Section 1807.1.6.3.
- Solid grouted hollow units or solid masonry units.
- A design in compliance with Chapter 21 or reinforcement in accordance with Table 1807.1.6.3(2) is required.
- For height of unbalanced backfill, see Section 1807.1.2.
- Where unbalanced backfill height exceeds 8 feet and design lateral soil loads from Table 1610.1 are used, the requirements for 30 and 45 psf per foot of depth are not applicable (see Section 1610).
TABLE 1807.1.6.3(2)
8-INCH MASONRY FOUNDATION WALLS WITH REINFORCEMENT WHERE d ≥ 5 INCHESa, b, c
MAXIMUM WALL HEIGHT (feet-inches) |
MAXIMUM UNBALANCED BACKFILL HEIGHTd (feet-inches) |
MINIMUM VERTICAL REINFORCEMENT-BAR SIZE AND SPACING (inches) | ||
Design lateral soil loada (psf per foot of depth) |
||||
30e | 45e | 60 | ||
7-4 | 4-0 (or less) | #4 at 48 | #4 at 48 | #4 at 48 |
5-0 | #4 at 48 | #4 at 48 | #4 at 48 | |
6-0 | #4 at 48 | #5 at 48 | #5 at 48 | |
7-4
|
#5 at 48
|
#6 at 48
|
#7 at 48
|
|
8-0 | 4-0 (or less) | #4 at 48 | #4 at 48 | #4 at 48 |
5-0 | #4 at 48 | #4 at 48 | #4 at 48 | |
6-0 | #4 at 48 | #5 at 48 | #5 at 48 | |
7-0
|
#5 at 48 |
#6 at 48
|
#7 at 48
|
|
8-0 | #5 at 48 | #6 at 48 | #7 at 48 | |
8-8 | 4-0 (or less) | #4 at 48 | #4 at 48 | #4 at 48 |
5-0 | #4 at 48 | #4 at 48 | #5 at 48 | |
6-0 | #4 at 48 | #5 at 48 | #6 at 48 | |
7-0
|
#5 at 48 |
#6 at 48
|
#7 at 48
|
|
8-8e | #6 at 48 | #7 at 48 | #8 at 48 | |
9-4 | 4-0 (or less) | #4 at 48 | #4 at 48 | #4 at 48 |
5-0 | #4 at 48 | #4 at 48 | #5 at 48 | |
6-0 | #4 at 48 | #5 at 48 | #6 at 48 | |
7-0
|
#5 at 48 |
#6 at 48
|
#7 at 48
|
|
8-0 | #6 at 48 | #7 at 48 | #8 at 48 | |
9-4e
|
#7 at 48
|
#8 at 48
|
#9 at 48 | |
10-0 | 4-0 (or less) | #4 at 48 | #4 at 48 | #4 at 48 |
5-0 | #4 at 48 | #4 at 48 | #5 at 48 | |
6-0 | #4 at 48 | #5 at 48 | #6 at 48 | |
7-0
|
#5 at 48 |
#6 at 48
|
#7 at 48
|
|
8-0 | #6 at 48 | #7 at 48 | #8 at 48 | |
9-0e
|
#7 at 48
|
#8 at 48
|
#9 at 48 | |
10-0e | #7 at 48 | #9 at 48 | #9 at 48 |
For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 pound per square foot per foot = 0.157 kPa/m.
- For design lateral soil loads, see Section 1610.
- Provisions for this table are based on design and construction requirements specified in Section 1807.1.6.3.
- For alternative reinforcement, see Section 1807.1.6.3.1.
- For height of unbalanced backfill, see Section 1807.1.2.
- Where unbalanced backfill height exceeds 8 feet and design lateral soil loads from Table 1610.1 are used, the requirements for 30 and 45 psf per foot of depth are not applicable. See Section 1610.
TABLE 1807.1.6.3(3)
10-INCH MASONRY FOUNDATION WALLS WITH REINFORCEMENT WHERE d ≥ 6.75 INCHESa, b, c
MAXIMUM WALL HEIGHT (feet-inches) |
MAXIMUM UNBALANCED BACKFILL HEIGHTd (feet-inches) |
MINIMUM VERTICAL REINFORCEMENT-BAR SIZE AND SPACING (inches) | ||
Design lateral soil loada (psf per foot of depth) | ||||
30e | 45e | 60 | ||
7-4 | 4-0 (or less) | #4 at 56 | #4 at 56 | #4 at 56 |
5-0 | #4 at 56 | #4 at 56 | #4 at 56 | |
6-0 | #4 at 56 | #4 at 56 | #5 at 56 | |
7-4
|
#4 at 56
|
#5 at 56
|
#6 at 56
|
|
8-0 | 4-0 (or less) | #4 at 56 | #4 at 56 | #4 at 56 |
5-0 | #4 at 56 | #4 at 56 | #4 at 56 | |
6-0 | #4 at 56 | #4 at 56 | #5 at 56 | |
7-0
|
#4 at 56
|
#5 at 56
|
#6 at 56
|
|
8-0 | #5 at 56 | #6 at 56 | #7 at 56 | |
8-8 | 4-0 (or less) | #4 at 56 | #4 at 56 | #4 at 56 |
5-0 | #4 at 56 | #4 at 56 | #4 at 56 | |
6-0 | #4 at 56 | #4 at 56 | #5 at 56 | |
7-0
|
#4 at 56
|
#5 at 56
|
#6 at 56
|
|
8-8e | #5 at 56 | #7 at 56 | #8 at 56 | |
9-4 | 4-0 (or less) | #4 at 56 | #4 at 56 | #4 at 56 |
5-0 | #4 at 56 | #4 at 56 | #4 at 56 | |
6-0 | #4 at 56 | #5 at 56 | #5 at 56 | |
7-0
|
#4 at 56
|
#5 at 56
|
#6 at 56
|
|
8-0 | #5 at 56 | #6 at 56 | #7 at 56 | |
9-4e
|
#6 at 56
|
#7 at 56
|
#7 at 56
|
|
10-0 | 4-0 (or less) | #4 at 56 | #4 at 56 | #4 at 56 |
5-0 | #4 at 56 | #4 at 56 | #4 at 56 | |
6-0 | #4 at 56 | #5 at 56 | #5 at 56 | |
7-0
|
#5 at 56
|
#6 at 56
|
#7 at 56
|
|
8-0 | #5 at 56 | #7 at 56 | #8 at 56 | |
9-0e
|
#6 at 56
|
#7 at 56
|
#9 at 56
|
|
10-0e | #7 at 56 | #8 at 56 | #9 at 56 |
For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 pound per square foot per foot = 1.157 kPa/m.
- For design lateral soil loads, see Section 1610.
- Provisions for this table are based on design and construction requirements specified in Section 1807.1.6.3.
- For alternative reinforcement, see Section 1807.1.6.3.1.
- For height of unbalanced backfill, see Section 1807.1.2.
- Where unbalanced backfill height exceeds 8 feet and design lateral soil loads from Table 1610.1 are used, the requirements for 30 and 45 psf per foot of depth are not applicable. See Section 1610.
TABLE 1807.1.6.3(4)
12-INCH MASONRY FOUNDATION WALLS WITH REINFORCEMENT WHERE d ≥ 8.75 INCHESa, b, c
MAXIMUM WALL HEIGHT (feet-inches) |
MAXIMUM UNBALANCED BACKFILL HEIGHTd (feet-inches) |
MINIMUM VERTICAL REINFORCEMENT-BAR SIZE AND SPACING (inches) | ||
Design lateral soil loada (psf per foot of depth) | ||||
30e | 45e | 60 | ||
7-4 | 4 (or less) | #4 at 72 | #4 at 72 | #4 at 72 |
5-0 | #4 at 72 | #4 at 72 | #4 at 72 | |
6-0 | #4 at 72 | #4 at 72 | #5 at 72 | |
7-4
|
#4 at 72
|
#5 at 72
|
#6 at 72
|
|
8-0 | 4 (or less) | #4 at 72 | #4 at 72 | #4 at 72 |
5-0 | #4 at 72 | #4 at 72 | #4 at 72 | |
6-0 | #4 at 72 | #4 at 72 | #5 at 72 | |
7-0
|
#4 at 72
|
#5 at 72
|
#6 at 72
|
|
8-0 | #5 at 72 | #6 at 72 | #8 at 72 | |
8-8 | 4 (or less) | #4 at 72 | #4 at 72 | #4 at 72 |
5-0 | #4 at 72 | #4 at 72 | #4 at 72 | |
6-0 | #4 at 72 | #4 at 72 | #5 at 72 | |
7-0
|
#4 at 72
|
#5 at 72
|
#6 at 72
|
|
8-8e | #5 at 72 | #7 at 72 | #8 at 72 | |
9-4 | 4 (or less) | #4 at 72 | #4 at 72 | #4 at 72 |
5-0 | #4 at 72 | #4 at 72 | #4 at 72 | |
6-0 | #4 at 72 | #4 at 72 | #5 at 72 | |
7-0
|
#4 at 72
|
#5 at 72
|
#6 at 72
|
|
8-0 | #5 at 72 | #6 at 72 | #7 at 72 | |
9-4e
|
#6 at 72
|
#7 at 72
|
#8 at 72
|
|
10-0 | 4 (or less) | #4 at 72 | #4 at 72 | #4 at 72 |
5-0 | #4 at 72 | #4 at 72 | #4 at 72 | |
6-0 | #4 at 72 | #5 at 72 | #5 at 72 | |
7-0
|
#4 at 72
|
#6 at 72
|
#6 at 72
|
|
8-0 | #5 at 72 | #6 at 72 | #7 at 72 | |
9-0e
|
#6 at 72
|
#7 at 72
|
#8 at 72
|
|
10-0e | #7 at 72 | #8 at 72 | #9 at 72 |
For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 pound per square foot per foot = 0.157 kPa/m.
- For design lateral soil loads, see Section 1610.
- Provisions for this table are based on design and construction requirements specified in Section 1807.1.6.3.
- For alternative reinforcement, see Section 1807.1.6.3.1.
- For height of unbalanced backfill, see Section 1807.1.2.
- Where unbalanced backfill height exceeds 8 feet and design lateral soil loads from Table 1610.1 are used, the requirements for 30 and 45 psf per foot of depth are not applicable. See Section 1610.
In lieu of the reinforcement provisions for masonry foundation walls in Table 1807.1.6.3(2), 1807.1.6.3(3) or 1807.1.6.3(4), alternative reinforcing bar sizes and spacings having an equivalent cross-sectional area of reinforcement per linear foot (mm) of wall shall be permitted to be used, provided that the spacing of reinforcement does not exceed 72 inches (1829 mm) and reinforcing bar sizes do not exceed No. 11.
Based on the seismic design category assigned to the structure in accordance with Section 1613, masonry foundation walls designed using Tables 1807.1.6.3(1) through 1807.1.6.3(4) shall be subject to the following limitations:
- Seismic Design Categories A and B. No additional seismic requirements.
- Seismic Design Category C. A design using Tables 1807.1.6.3(1) through 1807.1.6.3(4) is subject to the seismic requirements of Section 7.4.3 of TMS 402.
- Seismic Design Category D. A design using Tables 1807.1.6.3(2) through 1807.1.6.3(4) is subject to the seismic requirements of Section 7.4.4 of TMS 402.
- Seismic Design Categories E and F. A design using Tables 1807.1.6.3(2) through 1807.1.6.3(4) is subject to the seismic requirements of Section 7.4.5 of TMS 402.
Retaining walls shall be designed to resist the lateral action of soil to produce sliding and overturning with a minimum safety factor of 1.5 in each case. The load combinations of Section 1605 shall not apply to this requirement. Instead, design shall be based on 0.7 times nominal earthquake loads, 1.0 times other nominal loads, and investigation with one or more of the variable loads set to zero. The safety factor against lateral sliding shall be taken as the available soil resistance at the base of the retaining wall foundation divided by the net lateral force applied to the retaining wall.
Exception: Where earthquake loads are included, the minimum safety factor for retaining wall sliding and overturning shall be 1.1.
The design procedures outlined in this section are subject to the following limitations:
- The frictional resistance for structural walls and slabs on silts and clays shall be limited to one-half of the normal force imposed on the soil by the weight of the footing or slab.
- Posts embedded in earth shall not be used to provide lateral support for structural or nonstructural materials such as plaster, masonry or concrete unless bracing is provided that develops the limited deflection required.
Wood poles shall be treated in accordance with AWPA U1 for sawn timber posts (Commodity Specification A, Use Category 4B) and for round timber posts (Commodity Specification B, Use Category 4B).
The following formula shall be used in determining the depth of embedment required to resist lateral loads where lateral constraint is not provided at the ground surface, such as by a rigid floor or rigid ground surface pavement, and where lateral constraint is not provided above the ground surface, such as by a structural diaphragm.
(Equation 18-1)
where:
A = 2.34P/(S1b).
b = Diameter of round post or footing or diagonal dimension of square post or footing, feet (m).
d = Depth of embedment in earth in feet (m) but not over 12 feet (3658 mm) for purpose of computing lateral pressure.
h = Distance in feet (m) from ground surface to point of application of "P."
P = Applied lateral force in pounds (kN).
S1 = Allowable lateral soil-bearing pressure as set forth in Section 1806.2 based on a depth of one-third the depth of embedment in pounds per square foot (psf) (kPa).
The following formula shall be used to determine the depth of embedment required to resist lateral loads where lateral constraint is provided at the ground surface, such as by a rigid floor or pavement.
(Equation 18-2)
or alternatively
(Equation 18-3)
where:
Mg = Moment in the post at grade, in foot-pounds (kN-m).
S3 = Allowable lateral soil-bearing pressure as set forth in Section 1806.2 based on a depth equal to the depth of embedment in pounds per square foot (kPa).
The backfill in the annular space around columns not embedded in poured footings shall be by one of the following methods:
- Backfill shall be of concrete with a specified compressive strength of not less than 2,000 psi (13.8 MPa). The hole shall be not less than 4 inches (102 mm) larger than the diameter of the column at its bottom or 4 inches (102 mm) larger than the diagonal dimension of a square or rectangular column.
- Backfill shall be of clean sand. The sand shall be thoroughly compacted by tamping in layers not more than 8 inches (203 mm) in depth.
- Backfill shall be of controlled low-strength material (CLSM).
Fill or other surcharge loads shall not be placed adjacent to any building or structure unless such building or structure is capable of withstanding the additional loads caused by the fill or the surcharge. Existing footings or foundations that will be affected by any excavation shall be underpinned or otherwise protected against settlement and shall be protected against detrimental lateral or vertical movement or both.
Exception: Minor grading for landscaping purposes shall be permitted where done with walk-behind equipment, where the grade is not increased more than 1 foot (305 mm) from original design grade or where approved by the building official.
Foundations for buildings and structures founded on expansive soils shall be designed in accordance with Section 1808.6.1 or 1808.6.2.
Exception: Foundation design need not comply with Section 1808.6.1 or 1808.6.2 where one of the following conditions is satisfied:
- The soil is removed in accordance with Section 1808.6.3.
- The building official approves stabilization of the soil in accordance with Section 1808.6.4.
Foundations placed on or within the active zone of expansive soils shall be designed to resist differential volume changes and to prevent structural damage to the supported structure. Deflection and racking of the supported structure shall be limited to that which will not interfere with the usability and serviceability of the structure.
Foundations placed below where volume change occurs or below expansive soil shall comply with the following provisions:
- Foundations extending into or penetrating expansive soils shall be designed to prevent uplift of the supported structure.
- Foundations penetrating expansive soils shall be designed to resist forces exerted on the foundation due to soil volume changes or shall be isolated from the expansive soil.
Where expansive soil is removed in lieu of designing foundations in accordance with Section 1808.6.1 or 1808.6.2, the soil shall be removed to a depth sufficient to ensure a constant moisture content in the remaining soil. Fill material shall not contain expansive soils and shall comply with Section 1804.5 or 1804.6.
Exception: Expansive soil need not be removed to the depth of constant moisture, provided that the confining pressure in the expansive soil created by the fill and supported structure exceeds the swell pressure.
In general, buildings below slopes shall be set a sufficient distance from the slope to provide protection from slope drainage, erosion and shallow failures. Except as provided in Section 1808.7.5 and Figure 1808.7.1, the following criteria will be assumed to provide this protection. Where the existing slope is steeper than one unit vertical in one unit horizontal (100-percent slope), the toe of the slope shall be assumed to be at the intersection of a horizontal plane drawn from the top of the foundation and a plane drawn tangent to the slope at an angle of 45 degrees (0.79 rad) to the horizontal. Where a retaining wall is constructed at the toe of the slope, the height of the slope shall be measured from the top of the wall to the top of the slope.
For SI: 1 foot = 304.8 mm.
FOUNDATION CLEARANCES FROM SLOPES
The design, materials and construction of concrete foundations shall comply with Sections 1808.8.1 through 1808.8.6 and the provisions of Chapter 19.
Exception: [OSHPD 1R, 2 & 5] Not permitted by OSHPD. Where concrete footings supporting walls of light-frame construction are designed in accordance with Table 1809.7, a specific design in accordance with Chapter 19 is not required.
Concrete or grout in foundations shall have a specified compressive strength (f 'c) not less than the largest applicable value indicated in Table 1808.8.1.
Where concrete is placed through a funnel hopper at the top of a deep foundation element, the concrete mix shall be designed and proportioned so as to produce a cohesive workable mix having a slump of not less than 4 inches (102 mm) and not more than 8 inches (204 mm). Where concrete or grout is to be pumped, the mix design including slump shall be adjusted to produce a pumpable mixture.
MINIMUM SPECIFIED COMPRESSIVE STRENGTH f'c OF CONCRETE OR GROUT
FOUNDATION ELEMENT OR CONDITION | SPECIFIED COMPRESSIVE STRENGTH, f 'c |
1. Foundations for structures assigned to Seismic Design Category A, B or C.
[OSHPD 1R, 2 & 5] Not permitted by OSHPD. | 2,500 psi |
2a. Foundations for Group R or U occupancies of light-frame construction, two stories or less in | 2,500 psi |
2b. Foundations for other structures assigned to Seismic Design Category D, E or F | 3,000 psi |
3. Precast nonprestressed driven piles | 4,000 psi |
4. Socketed drilled shafts | 4,000 psi |
5. Micropiles | 4,000 psi |
6. Precast prestressed driven piles | 5,000 psi |
For SI: 1 pound per square inch = 0.00689 MPa.
The concrete cover provided for prestressed and nonprestressed reinforcement in foundations shall be not less than the largest applicable value specified in Table 1808.8.2. Longitudinal bars spaced less than 11/2 inches (38 mm) clear distance apart shall be considered to be bundled bars for which the concrete cover provided shall be not less than that required by Section 20.6.1.3.4 of ACI 318. Concrete cover shall be measured from the concrete surface to the outermost surface of the steel to which the cover requirement applies. Where concrete is placed in a temporary or permanent casing or a mandrel, the inside face of the casing or mandrel shall be considered to be the concrete surface.
TABLE 1808.8.2
MINIMUM CONCRETE COVER
FOUNDATION ELEMENT OR CONDITION | MINIMUM COVER |
1. Shallow foundations | In accordance with Section 20.6 of ACI 318 |
2. Precast nonprestressed deep foundation elements | |
Exposed to seawater | 3 inches |
Not manufactured under plant conditions
|
2 inches |
Manufactured under plant control conditions | In accordance with Section 20.6.1.3.3 of ACI 318 |
3. Precast prestressed deep foundation elements | |
Exposed to seawater | 2.5 inches |
Other | In accordance with Section 20.6.1.3.3 ofACI 318 |
4. Cast-in-place deep foundation elements not enclosed by a steel pipe, tube or permanent casing | 2.5 inches |
5. Cast-in-place deep foundation elements enclosed by a steel pipe, tube or permanent casing | 1 inch |
6. Structural steel core within a steel pipe, tube or permanent casing | 2 inches |
7. Cast-in-place drilled shafts enclosed by a stable rock socket | 1.5 inches |
For SI: 1 inch = 25.4 mm.
[OSHPD 1R, 2 & 5] See Section 1905 for additional requirements for foundations of structures assigned to Seismic Design Category C, D, E or F.
For structures assigned to Seismic Design Category D, E or F, provisions of Section 18.13 of ACI 318 shall apply where not in conflict with the provisions of Sections 1808 through 1810.
Exceptions: [OSHPD 1R, 2 & 5] Not permitted by OSHPD.
- Detached one- and two-family dwellings of light-frame construction and two stories or less above grade plane are not required to comply with the provisions of Section 18.13 of ACI 318.
- Section 18.13.4.3(a) of ACI 318 shall not apply.
STEPPED FOUNDATIONS
Except where otherwise protected from frost, foundations and other permanent supports of buildings and structures shall be protected from frost by one or more of the following methods:
- Extending below the frost line of the locality.
- Constructing in accordance with ASCE 32.
Erecting on solid rock.
Exception: Free-standing buildings meeting all of the following conditions shall not be required to be protected:
- Assigned to Risk Category I.
- Area of 600 square feet (56 m2) or less for light-frame construction or 400 square feet (37 m2) or less for other than light-frame construction.
- Eave height of 10 feet (3048 mm) or less.
Shallow foundations shall not bear on frozen soil unless such frozen condition is of a permanent character.
NUMBER OF FLOORS SUPPORTED BY THE FOOTINGf |
WIDTH OF FOOTING (inches) |
THICKNESS OF FOOTING (inches) |
1 | 12 | 6 |
2 | 15 | 6 |
3 | 18 | 8g |
- Depth of footings shall be in accordance with CBC Section 1809.4.
- The ground under the floor shall be is permitted to be excavated to the elevation of the top of the footing.
- Interior stud-bearing walls shall be permitted to be supported by isolated footings. The footing width and length shall be twice the width shown in this table, and footings shall be spaced not more than 6 feet on center. Not adopted.
- See CBC Section 1905 1908 for additional requirements for concrete footings of structures assigned to Seismic Design Category C, D, E or F.
- For thickness of foundation walls, see Section 1807.1.6 LAMC Subdivision 91.1807.1.6.
- Footings shall be are permitted to support a roof in addition to the stipulated number of floors. Footings supporting roof only shall be as required for supporting one floor.
- Plain concrete footings for Group R-3 occupancies shall be permitted to be 6 inches thick.
[OSHPD 1R, 2 & 5] Not permitted by OSHPD. The edge thickness of plain concrete footings supporting walls of other than light-frame construction shall be not less than 8 inches (203 mm) where placed on soil or rock.
Exception: For plain concrete footings supporting Group R-3 occupancies, the edge thickness is permitted to be 6 inches (152 mm), provided that the footing does not extend beyond a distance greater than the thickness of the footing on either side of the supported wall.
[OSHPD 1R, 2 & 5] Not permitted by OSHPD. The design, materials and construction of masonry-unit footings shall comply with Sections 1809.9.1 and 1809.9.2, and the provisions of Chapter 21.
Exception: Where a specific design is not provided, masonry-unit footings supporting walls of light-frame construction shall be permitted to be designed in accordance with Table 1809.7.
Except in Seismic Design Categories D, E and F, pier and curtain wall foundations shall be permitted to be used to support light-frame construction not more than two stories above grade plane, provided that the following requirements are met:
- All load-bearing walls shall be placed on continuous concrete footings bonded integrally with the exterior wall footings.
- The minimum actual thickness of a load-bearing masonry wall shall be not less than 4 inches (102 mm) nominal or 35/8 inches (92 mm) actual thickness, and shall be bonded integrally with piers spaced 6 feet (1829 mm) on center (o.c.).
Piers shall be constructed in accordance with Chapter 21 and the following:
- 3.1. The unsupported height of the masonry piers shall not exceed 10 times their least dimension.
3.2. Where structural clay tile or hollow concrete masonry units are used for piers supporting beams and girders, the cellular spaces shall be filled solidly with concrete or Type M or S mortar.
Exception: Unfilled hollow piers shall be permitted where the unsupported height of the pier is not more than four times its least dimension.
- 3.3. Hollow piers shall be capped with 4 inches (102 mm) of solid masonry or concrete or the cavities of the top course shall be filled with concrete or grout.
- The maximum height of a 4-inch (102 mm) load-bearing masonry foundation wall supporting wood frame walls and floors shall not be more than 4 feet (1219 mm) in height.
- The unbalanced fill for 4-inch (102 mm) foundation walls shall not exceed 24 inches (610 mm) for solid masonry, nor 12 inches (305 mm) for hollow masonry.
[OSHPD 1R, 2 & 5] Unless otherwise recommended by the soils report, open or backfilled trenches parallel with a footing shall not be below a plane having a downward slope of 1 unit vertical to 2 units horizontal (50-percent slope) from a line 9 inches (229 mm) above the bottom edge of the footing, and not closer than 18 inches (457 mm) from the face of such footing.
Where pipes cross under footings, the footings shall be specially designed. Pipe sleeves shall be provided where pipes cross through footings or footing walls and sleeve clearances shall provide for possible footing settlement, but not less than 1 inch (25 mm) all around pipe.
Deep foundation elements standing unbraced in air, water or fluid soils shall be classified as columns and designed as such in accordance with the provisions of this code from their top down to the point where adequate lateral support is provided in accordance with Section 1810.2.1.
Exception: Where the unsupported height to least horizontal dimension of a cast-in-place deep foundation element does not exceed three, it shall be permitted to design and construct such an element as a pedestal in accordance with ACI 318.
Any soil other than fluid soil shall be deemed to afford sufficient lateral support to prevent buckling of deep foundation elements and to permit the design of the elements in accordance with accepted engineering practice and the applicable provisions of this code.
Where deep foundation elements stand unbraced in air, water or fluid soils, it shall be permitted to consider them laterally supported at a point 5 feet (1524 mm) into stiff soil or 10 feet (3048 mm) into soft soil unless otherwise approved by the building official on the basis of a geotechnical investigation by a registered design professional.
Deep foundation elements shall be braced to provide lateral stability in all directions. Three or more elements connected by a rigid cap shall be considered to be braced, provided that the elements are located in radial directions from the centroid of the group not less than 60 degrees (1 rad) apart. A two-element group in a rigid cap shall be considered to be braced along the axis connecting the two elements. Methods used to brace deep foundation elements shall be subject to the approval of the building official.
Deep foundation elements supporting walls shall be placed alternately in lines spaced not less than 1 foot (305 mm) apart and located symmetrically under the center of gravity of the wall load carried, unless effective measures are taken to provide for eccentricity and lateral forces, or the foundation elements are adequately braced to provide for lateral stability.
Exceptions:
- Isolated cast-in-place deep foundation elements without lateral bracing shall be permitted where the least horizontal dimension is not less than 2 feet (610 mm), adequate lateral support in accordance with Section 1810.2.1 is provided for the entire height and the height does not exceed 12 times the least horizontal dimension.
- A single row of deep foundation elements without lateral bracing is permitted for one- and two-family dwellings and lightweight construction not exceeding two stories above grade plane or 35 feet (10 668 mm) in building height, provided that the centers of the elements are located within the width of the supported wall.
For structures assigned to Seismic Design Category D, E or F, deep foundation elements on Site Class E or F sites, as determined in Section 1613.2.2, shall be designed and constructed to withstand maximum imposed curvatures from earthquake ground motions and structure response. Curvatures shall include free-field soil strains modified for soil-foundation-structure interaction coupled with foundation element deformations associated with earthquake loads imparted to the foundation by the structure.
Exception: Deep foundation elements that satisfy the following additional detailing requirements shall be deemed to comply with the curvature capacity requirements of this section.
- Precast prestressed concrete piles detailed in accordance with Section 1810.3.8.3.3.
- Cast-in-place deep foundation elements with a minimum longitudinal reinforcement ratio of 0.005 extending the full length of the element and detailed in accordance with Sections 18.7.5.2, 18.7.5.3 and 18.7.5.4 of ACI 318 as required by Section 1810.3.9.4.2.2.
The allowable stresses for materials used in deep foundation elements shall not exceed those specified in Table 1810.3.2.6.
TABLE 1810.3.2.6
ALLOWABLE STRESSES FOR MATERIALS USED IN DEEP FOUNDATION ELEMENTS
MATERIAL TYPE AND CONDITION | MAXIMUM ALLOWABLE STRESSa |
1. Concrete or grout in compressionb | |
Cast-in-place with a permanent casing in accordance with Section 1810.3.2.7
|
0.4 f'c |
Cast-in-place in a pipe, tube, other permanent casing or rock
|
0.33 f'c |
Cast-in-place without a permanent casing
|
0.3f'c |
Precast nonprestressed
|
0.33f'c |
Precast prestressed
|
0.33f 'c-0.27 fpc |
2. Nonprestressed reinforcement in compression | 0.4 fy ≤ 30,000 psi |
3. Steel in compression | |
Cores within concrete-filled pipes or tubes |
0.5 Fy≤ 32,000 psi |
Pipes, tubes or H-piles, where justified in accordance with Section 1810.3.2.8 |
0.5 Fy≤ 32,000 psi |
Pipes or tubes for micropiles |
0.4 Fy≤ 32,000 psi |
Other pipes, tubes or H-piles |
0.35 Fy≤ 16,000 psi |
0.6 Fy≤ 0.5 Fu | |
4. Nonprestressed reinforcement in tension | 0.6 fy 0.5 fy≤ 24,000 psi0.6 fy |
Within micropiles |
|
Other conditions |
0.5 fy≤ 24,000 psi |
5. Steel in tension | |
Pipes, tubes or H-piles, where justified in accordance with Section 1810.3.2.8 |
0.5Fy≤ 32,000 psi |
Other pipes, tubes or H-piles |
0.35 Fy≤ 16,000 psi |
0.6 Fy ≤ 0.5 Fu | |
6. Timber | In accordance with the ANSI/AWC NDS |
- f 'c is the specified compressive strength of the concrete or grout; fpc is the compressive stress on the gross concrete section due to effective prestress forces only; fy is the specified yield strength of reinforcement; Fy is the specified minimum yield stress of steel; Fu is the specified minimum tensile stress of structural steel.
- The stresses specified apply to the gross cross-sectional area within the concrete surface. Where a temporary or permanent casing is used, the inside face of the casing shall be considered to be the concrete surface.
The allowable compressive stress in the concrete shall be permitted to be increased as specified in Table 1810.3.2.6 for those portions of permanently cased cast-in-place elements that satisfy all of the following conditions:
- The design shall not use the casing to resist any portion of the axial load imposed.
- The casing shall have a sealed tip and be mandrel driven.
- The thickness of the casing shall be not less than manufacturer's standard gage No.14 (0.068 inch) (1.75 mm).
- The casing shall be seamless or provided with seams of strength equal to the basic material and be of a configuration that will provide confinement to the cast-in-place concrete.
- The ratio of steel yield strength (Fy) to specified compressive strength (f 'c) shall be not less than six.
- The nominal diameter of the element shall not be greater than 16 inches (406 mm).
Use of allowable stresses greater than those specified in Section 1810.3.2.6 shall be permitted where supporting data justifying such higher stresses is filed with the building official. Such substantiating data shall include the following:
- A geotechnical investigation in accordance with Section 1803.
- Load tests in accordance with Section 1810.3.3.1.2, regardless of the load supported by the element.
The design and installation of the deep foundation elements shall be under the direct supervision of a registered design professional knowledgeable in the field of soil mechanics and deep foundations who shall submit a report to the building official stating that the elements as installed satisfy the design criteria.
It shall be permitted to evaluate load tests of deep foundation elements using any of the following methods:
- Davisson Offset Limit.
- Brinch-Hansen 90-percent Criterion.
- Butler-Hoy Criterion.
- Other methods approved by the building official.
Where required by the design, the uplift capacity of a single deep foundation element shall be determined by an approved method of analysis based on a minimum factor of safety of three or by load tests conducted in accordance with ASTM D3689. The maximum allowable uplift load shall not exceed the ultimate load capacity as determined in Section 1810.3.3.1.2, using the results of load tests conducted in accordance with ASTM D3689, divided by a factor of safety of two.
Exception: Where uplift is due to wind or seismic loading, the minimum factor of safety shall be two where capacity is determined by an analysis and one and one-half where capacity is determined by load tests.
For grouped deep foundation elements subjected to uplift, the allowable uplift load for the group shall be calculated by a generally accepted method of analysis. Where the deep foundation elements in the group are placed at a center-to-center spacing less than three times the least horizontal dimension of the largest single element, the allowable uplift load for the group is permitted to be calculated as the lesser of:
- The proposed individual allowable uplift load times the number of elements in the group.
- Two-thirds of the effective weight of the group and the soil contained within a block defined by the perimeter of the group and the length of the element, plus two-thirds of the ultimate shear resistance along the soil block.
The allowable axial design load, Pa, of helical piles shall be determined as follows:
(Equation 18-4)
where Pu is the least value of:
- Sum of the areas of the helical bearing plates times the ultimate bearing capacity of the soil or rock comprising the bearing stratum.
- Ultimate capacity determined from well-documented correlations with installation torque.
- Ultimate capacity determined from load tests.
- Ultimate axial capacity of pile shaft.
- Ultimate axial capacity of pile shaft couplings.
- Sum of the ultimate axial capacity of helical bearing plates affixed to pile.
Where deep foundation elements are installed through subsiding fills or other subsiding strata and derive support from underlying firmer materials, consideration shall be given to the downward frictional forces potentially imposed on the elements by the subsiding upper strata.
Where the influence of subsiding fills is considered as imposing loads on the element, the allowable stresses specified in this chapter shall be permitted to be increased where satisfactory substantiating data are submitted.
Cast-in-place or grouted-in-place deep foundation elements without a permanent casing shall have a specified diameter of not less than 12 inches (305 mm). The element length shall not exceed 30 times the specified diameter.
Exception: The length of the element is permitted to exceed 30 times the specified diameter, provided that the design and installation of the deep foundations are under the direct supervision of a registered design professional knowledgeable in the field of soil mechanics and deep foundations. The registered design professional shall submit a report to the building official stating that the elements were installed in compliance with the approved construction documents.
Sections of structural steel H-piles shall comply with the requirements for HP shapes in ASTM A6, or the following:
- The flange projections shall not exceed 14 times the minimum thickness of metal in either the flange or the web and the flange widths shall be not less than 80 percent of the depth of the section.
- The nominal depth in the direction of the web shall be not less than 8 inches (203 mm).
- Flanges and web shall have a minimum nominal thickness of 3/8 inch (9.5 mm).
Sections of fully welded steel piles fabricated from plates shall comply with the following:
- The flange projections shall not exceed 14 times the minimum thickness of metal in either the flange or the web and the flange widths shall be not less than 80 percent of the depth of the section.
- The nominal depth in the direction of the web shall be not less than 8 inches (203 mm).
- Flanges and web shall have a minimum nominal thickness of 3/8 inch (9.5 mm).
[OSHPD 1R, 2 & 5] Installation of sheet piling shall satisfy inspection, monitoring, and observation requirements in Sections 1812.6 and 1812.7.
Steel pipes and tubes used as deep foundation elements shall have a nominal outside diameter of not less than 8 inches (203 mm). Where steel pipes or tubes are driven open ended, they shall have not less than 0.34 square inch (219 mm2) of steel in cross section to resist each 1,000 foot-pounds (1356 Nm) of pile hammer energy, or shall have the equivalent strength for steels having a yield strength greater than 35,000 psi (241 MPa) or the wave equation analysis shall be permitted to be used to assess compression stresses induced by driving to evaluate if the pile section is appropriate for the selected hammer. Where a pipe or tube with wall thickness less than 0.179 inch (4.6 mm) is driven open ended, a suitable cutting shoe shall be provided. Concrete-filled steel pipes or tubes in structures assigned to Seismic Design Category C, D, E or F shall have a wall thickness of not less than 3/16 inch (5 mm). The pipe or tube casing for socketed drilled shafts shall have a nominal outside diameter of not less than 18 inches (457 mm), a wall thickness of not less than 3/8 inch (9.5 mm) and a suitable steel driving shoe welded to the bottom; the diameter of the rock socket shall be approximately equal to the inside diameter of the casing.
Exceptions:
- There is no minimum diameter for steel pipes or tubes used in micropiles.
- For mandrel-driven pipes or tubes, the minimum wall thickness shall be 1/10 inch (2.5 mm).
Splices shall be constructed so as to provide and maintain true alignment and position of the component parts of the deep foundation element during installation and subsequent thereto and shall be designed to resist the axial and shear forces and moments occurring at the location of the splice during driving and for design load combinations. Where deep foundation elements of the same type are being spliced, splices shall develop not less than 50 percent of the bending strength of the weaker section. Where deep foundation elements of different materials or different types are being spliced, splices shall develop the full compressive strength and not less than 50 percent of the tension and bending strength of the weaker section. Where structural steel cores are to be spliced, the ends shall be milled or ground to provide full contact and shall be full-depth welded.
Splices occurring in the upper 10 feet (3048 mm) of the embedded portion of an element shall be designed to resist at allowable stresses the moment and shear that would result from an assumed eccentricity of the axial load of 3 inches (76 mm), or the element shall be braced in accordance with Section 1810.2.2 to other deep foundation elements that do not have splices in the upper 10 feet (3048 mm) of embedment.
For structures assigned to Seismic Design Category C, D, E or F splices of deep foundation elements shall develop the lesser of the following:
- The nominal strength of the deep foundation element.
- The axial and shear forces and moments from the seismic load effects including overstrength factor in accordance with Section 2.3.6 or 2.4.5 of ASCE 7.
Longitudinal steel shall be arranged in a symmetrical pattern and be laterally tied with steel ties or wire spiral spaced center to center as follows:
- At not more than 1 inch (25 mm) for the first five ties or spirals at each end; then
- At not more than 4 inches (102 mm), for the remainder of the first 2 feet (610 mm) from each end; and then
- At not more than 6 inches (152 mm) elsewhere.
The size of ties and spirals shall be as follows:
- For piles having a least horizontal dimension of 16 inches (406 mm) or less, wire shall not be smaller than 0.22 inch (5.6 mm) (No. 5 gage).
- For piles having a least horizontal dimension of more than 16 inches (406 mm) and less than 20 inches (508 mm), wire shall not be smaller than 0.238 inch (6 mm) (No. 4 gage).
- For piles having a least horizontal dimension of 20 inches (508 mm) and larger, wire shall not be smaller than 1/4 inch (6.4 mm) round or 0.259 inch (6.6 mm) (No. 3 gage).
The effective prestress in the pile shall be not less than 400 psi (2.76 MPa) for piles up to 30 feet (9144 mm) in length, 550 psi (3.79 MPa) for piles up to 50 feet (15 240 mm) in length and 700 psi (4.83 MPa) for piles greater than 50 feet (15 240 mm) in length.
Effective prestress shall be based on an assumed loss of 30,000 psi (207 MPa) in the prestressing steel. The tensile stress in the prestressing steel shall not exceed the values specified in ACI 318.
where: | ||
Ag | = | Pile cross-sectional area square inches (mm2). |
f 'c | = | Specified compressive strength of concrete, psi (MPa). |
fyh | = | Yield strength of spiral reinforcement ≤ 85,000 psi (586 MPa). |
P | = | Axial load on pile, pounds (kN), as determined from Equations 16-5 and 16-7. |
ρs | = | Spiral reinforcement index or volumetric ratio (vol. spiral/vol. core). |
For structures assigned to Seismic Design Category D, E or F, precast prestressed piles shall have transverse reinforcement in accordance with the following:
- Requirements in ACI 318, Chapter 18, need not apply, unless specifically referenced.
- Where the total pile length in the soil is 35 feet (10 668 mm) or less, the lateral transverse reinforcement in the ductile region shall occur through the length of the pile. Where the pile length exceeds 35 feet (10 668 mm), the ductile pile region shall be taken as the greater of 35 feet (10 668 mm) or the distance from the underside of the pile cap to the point of zero curvature plus three times the least pile dimension.
- In the ductile region, the center-to-center spacing of the spirals or hoop reinforcement shall not exceed one-fifth of the least pile dimension, six times the diameter of the longitudinal strand or 8 inches (203 mm), whichever is smallest.
- Circular spiral reinforcement shall be spliced by lapping one full turn and bending the end of each spiral to a 90-degree hook or by use of a mechanical or welded splice complying with Section 25.5.7 of ACI 318.
Where the transverse reinforcement consists of circular spirals, the volumetric ratio of spiral transverse reinforcement in the ductile region shall comply with the following:
(Equation 18-6)
but not exceed:
(Equation 18-7)
where:
Ag = Pile cross-sectional area, square inches (mm2).
f 'c = Specified compressive strength of concrete, psi (MPa).
fyh = Yield strength of spiral reinforcement = ≤ 85,000 psi (586 MPa).
P = Axial load on pile, pounds (kN), as determined from Equations 16-5 and 16-7.
ρs = Volumetric ratio (vol. spiral/vol. core).
This required amount of spiral reinforcement is permitted to be obtained by providing an inner and outer spiral.
Exception: [OSHPD 1R, 2 & 5] Not permitted by OSHPD. The minimum spiral reinforcement required by Equation 18-6 shall not apply in cases where the design includes full consideration of load combinations specified in ASCE 7, Section 2.3.6 and the applicable overstrength factor, Ω0. In such cases, minimum spiral reinforcement shall be as specified in Section 1810.3.8.1.
Where transverse reinforcement consists of rectangular hoops and cross ties, the total cross-sectional area of lateral transverse reinforcement in the ductile region with spacing, s, and perpendicular dimension, hc, shall conform to:
(Equation 18-8)
but not less than:
(Equation 18-9)
where:
fyh = yield strength of transversereinforcement ≤70,000 psi (483 MPa).
hc = Cross-sectional dimension of pile core measured center to center of hoop reinforcement, inch (mm).
s = Spacing of transverse reinforcement measured along length of pile, inch (mm).
Ash = Cross-sectional area of transverse reinforcement, square inches (mm2).
f'c = Specified compressive strength of concrete, psi (MPa).
The hoops and cross ties shall be equivalent to deformed bars not less than No. 3 in size. Rectangular hoop ends shall terminate at a corner with seismic hooks.
Outside of the length of the pile requiring transverse confinement reinforcing, the spiral or hoop reinforcing with a volumetric ratio not less than one-half of that required for transverse confinement reinforcing shall be provided.
For structures assigned to Seismic Design Category C, D, E, or F, the maximum factored axial load on precast prestressed piles subjected to a combination of seismic lateral force and axial load shall not exceed the following values:
- 0.2f 'c Ag for square piles
- 0.4f 'c Ag for circular or octagonal piles
For SI:
where: | ||
f'c | = | Specified compressive strength of concrete or grout, psi (MPa). |
Sm | = | Elastic section modulus, neglecting reinforcement and casing, cubic inches (mm3). |
Reinforcement where required shall be assembled and tied together and shall be placed in the deep foundation element as a unit before the reinforced portion of the element is filled with concrete.
Exceptions:
- Steel dowels embedded 5 feet (1524 mm) or less shall be permitted to be placed after concreting, while the concrete is still in a semifluid state.
- For deep foundation elements installed with a hollow-stem auger, tied reinforcement shall be placed after elements are concreted, while the concrete is still in a semifluid state. Longitudinal reinforcement without lateral ties shall be placed either through the hollow stem of the auger prior to concreting or after concreting, while the concrete is still in a semifluid state.
- For Group R-3 and U occupancies not exceeding two stories of light-frame construction, reinforcement is permitted to be placed after concreting, while the concrete is still in a semifluid state, and the concrete cover requirement is permitted to be reduced to 2 inches (51 mm), provided that the construction method can be demonstrated to the satisfaction of the building official.
Where a structure is assigned to Seismic Design Category C, reinforcement shall be provided in accordance with Section 1810.3.9.4.1. Where a structure is assigned to Seismic Design Category D, E or F, reinforcement shall be provided in accordance with Section 1810.3.9.4.2.
Exceptions:
- Isolated deep foundation elements supporting posts of Group R-3 and U occupancies not exceeding two stories of light-frame construction shall be permitted to be reinforced as required by rational analysis but with not less than one No. 4 bar, without ties or spirals, where detailed so the element is not subject to lateral loads and the soil provides adequate lateral support in accordance with Section 1810.2.1.
- Isolated deep foundation elements supporting posts and bracing from decks and patios appurtenant to Group R-3 and U occupancies not exceeding two stories of light-frame construction shall be permitted to be reinforced as required by rational analysis but with not less than one No. 4 bar, without ties or spirals, where the lateral load, E, to the top of the element does not exceed 200 pounds (890 N) and the soil provides adequate lateral support in accordance with Section 1810.2.1.
- Deep foundation elements supporting the concrete foundation wall of Group R-3 and U occupancies not exceeding two stories of light-frame construction shall be permitted to be reinforced as required by rational analysis but with not less than two No. 4 bars, without ties or spirals, where the design cracking moment determined in accordance with Section 1810.3.9.1 exceeds the required moment strength determined using the load combinations with overstrength factor in Section 2.3.6 or 2.4.5 of ASCE 7 and the soil provides adequate lateral support in accordance with Section 1810.2.1.
- Closed ties or spirals where required by Section 1810.3.9.4.2 shall be permitted to be limited to the top 3 feet (914 mm) of deep foundation elements 10 feet (3048 mm) or less in depth supporting Group R-3 and U occupancies of Seismic Design Category D, not exceeding two stories of light-frame construction.
For structures assigned to Seismic Design Category C, cast-in-place deep foundation elements shall be reinforced as specified in this section. Reinforcement shall be provided where required by analysis.
Not fewer than four longitudinal bars, with a minimum longitudinal reinforcement ratio of 0.0025, shall be provided throughout the minimum reinforced length of the element as defined in this section starting at the top of the element. The minimum reinforced length of the element shall be taken as the greatest of the following:
- One-third of the element length.
- A distance of 10 feet (3048 mm).
- Three times the least element dimension.
- The distance from the top of the element to the point where the design cracking moment determined in accordance with Section 1810.3.9.1 exceeds the required moment strength determined using the load combinations of Section 1605.2.
Transverse reinforcement shall consist of closed ties or spirals with a minimum 3/8 inch (9.5 mm) diameter. Spacing of transverse reinforcement shall not exceed the smaller of 6 inches (152 mm) or 8-longitudinal-bar diameters, within a distance of three times the least element dimension from the bottom of the pile cap. Spacing of transverse reinforcement shall not exceed 16 longitudinal bar diameters throughout the remainder of the reinforced length.
Exceptions:
- The requirements of this section shall not apply to concrete cast in structural steel pipes or tubes.
- A spiral-welded metal casing of a thickness not less than the manufacturer's standard No. 14 gage (0.068 inch) is permitted to provide concrete confinement in lieu of the closed ties or spirals. Where used as such, the metal casing shall be protected against possible deleterious action due to soil constituents, changing water levels or other factors indicated by boring records of site conditions.
For structures assigned to Seismic Design Category D, E or F, cast-in-place deep foundation elements shall be reinforced as specified in this section. Reinforcement shall be provided where required by analysis.
Not fewer than four longitudinal bars, with a minimum longitudinal reinforcement ratio of 0.005, shall be provided throughout the minimum reinforced length of the element as defined in this section starting at the top of the element. The minimum reinforced length of the element shall be taken as the greatest of the following:
- One-half of the element length.
- A distance of 10 feet (3048 mm).
- Three times the least element dimension.
- The distance from the top of the element to the point where the design cracking moment determined in accordance with Section 1810.3.9.1 exceeds the required moment strength determined using the load combinations of Section 1605.2.
Transverse reinforcement shall consist of closed ties or spirals not smaller than No. 3 bars for elements with a least dimension up to 20 inches (508 mm), and No. 4 bars for larger elements. Throughout the remainder of the reinforced length outside the regions with transverse confinement reinforcement, as specified in Section 1810.3.9.4.2.1 or 1810.3.9.4.2.2, the spacing of transverse reinforcement shall not exceed the least of the following:
- 12 longitudinal bar diameters.
- One-half the least dimension of the element.
- 12 inches (305 mm).
Exceptions:
- The requirements of this section shall not apply to concrete cast in structural steel pipes or tubes.
- A spiral-welded metal casing of a thickness not less than manufacturer's standard No. 14 gage (0.068 inch) is permitted to provide concrete confinement in lieu of the closed ties or spirals. Where used as such, the metal casing shall be protected against possible deleterious action due to soil constituents, changing water levels or other factors indicated by boring records of site conditions.
Socketed drilled shafts shall have a permanent pipe or tube casing that extends down to bedrock and an uncased socket drilled into the bedrock, both filled with concrete. Socketed drilled shafts shall have reinforcement or a structural steel core for the length as indicated by an approved method of analysis.
The depth of the rock socket shall be sufficient to develop the full load-bearing capacity of the element with a minimum safety factor of two, but the depth shall be not less than the outside diameter of the pipe or tube casing. The design of the rock socket is permitted to be predicated on the sum of the allowable load-bearing pressure on the bottom of the socket plus bond along the sides of the socket.
Where a structural steel core is used, the gross cross-sectional area of the core shall not exceed 25 percent of the gross area of the drilled shaft.
Reinforcement shall consist of deformed reinforcing bars in accordance with ASTM A615 Grade 60 or 75 or ASTM A722 Grade 150.
The steel pipe or tube shall have a minimum wall thickness of 3/16 inch (4.8 mm). Splices shall comply with Section 1810.3.6. The steel pipe or tube shall have a minimum yield strength of 45,000 psi (310 MPa) and a minimum elongation of 15 percent as shown by mill certifications or two coupon test samples per 40,000 pounds (18 160 kg) of pipe or tube.
For structures assigned to Seismic Design Category C, D, E or F, concrete deep foundation elements shall be connected to the pile cap by embedding the element reinforcement or field-placed dowels anchored in the element into the pile cap for a distance equal to their development length in accordance with ACI 318. It shall be permitted to connect precast prestressed piles to the pile cap by developing the element prestressing strands into the pile cap provided that the connection is ductile. For deformed bars, the development length is the full development length for compression, or tension in the case of uplift, without reduction for excess reinforcement in accordance with Section 25.4.10 of ACI 318. Alternative measures for laterally confining concrete and maintaining toughness and ductile-like behavior at the top of the element shall be permitted provided that the design is such that any hinging occurs in the confined region.
The minimum transverse steel ratio for confinement shall be not less than one-half of that required for columns.
For resistance to uplift forces, anchorage of steel pipes, tubes or H-piles to the pile cap shall be made by means other than concrete bond to the bare steel section. Concrete-filled steel pipes or tubes shall have reinforcement of not less than 0.01 times the cross-sectional area of the concrete fill developed into the cap and extending into the fill a length equal to two times the required cap embedment, but not less than the development length in tension of the reinforcement.
For structures assigned to Seismic Design Category D, E or F, deep foundation element resistance to uplift forces or rotational restraint shall be provided by anchorage into the pile cap, designed considering the combined effect of axial forces due to uplift and bending moments due to fixity to the pile cap. Anchorage shall develop not less than 25 percent of the strength of the element in tension. Anchorage into the pile cap shall comply with the following:
In the case of uplift, the anchorage shall be capable of developing the least of the following:
- 1.1. The nominal tensile strength of the longitudinal reinforcement in a concrete element.
- 1.2. The nominal tensile strength of a steel element.
1.3. The frictional force developed between the element and the soil multiplied by 1.3.
Exception: The anchorage is permitted to be designed to resist the axial tension force resulting from the seismic load effects including overstrength factor in accordance with Section 2.3.6 or 2.4.5 of ASCE 7.
- In the case of rotational restraint, the anchorage shall be designed to resist the axial and shear forces, and moments resulting from the seismic load effects including overstrength factor in accordance with Section 2.3.6 or 2.4.5 of ASCE 7 or the anchorage shall be capable of developing the full axial, bending and shear nominal strength of the element.
Where the vertical lateral-force-resisting elements are columns, the pile cap flexural strengths shall exceed the column flexural strength. The connection between batter piles and pile caps shall be designed to resist the nominal strength of the pile acting as a short column. Batter piles and their connection shall be designed to resist forces and moments that result from the application of seismic load effects including overstrength factor in accordance with Section 2.3.6 or 2.4.5 of ASCE 7.
For structures assigned to Seismic Design Category C, D, E or F, individual deep foundations shall be interconnected by ties. Unless it can be demonstrated that equivalent restraint is provided by reinforced concrete beams within slabs on grade or reinforced concrete slabs on grade or confinement by competent rock, hard cohesive soils or very dense granular soils, ties shall be capable of carrying, in tension or compression, a force equal to the lesser of the product of the larger pile cap or column design gravity load times the seismic coefficient, SDS, divided by 10, and 25 percent of the smaller pile or column design gravity load.
Exception: In Group R-3 and U occupancies of light-frame construction, deep foundation elements supporting foundation walls, isolated interior posts detailed so the element is not subject to lateral loads or exterior decks and patios are not subject to interconnection where the soils are of adequate stiffness, subject to the approval of the building official.
Micropile deep foundation elements shall be permitted to be formed in holes advanced by rotary or percussive drilling methods, with or without casing. The elements shall be grouted with a fluid cement grout. The grout shall be pumped through a tremie pipe extending to the bottom of the element until grout of suitable quality returns at the top of the element. The following requirements apply to specific installation methods:
- For micropiles grouted inside a temporary casing, the reinforcing bars shall be inserted prior to withdrawal of the casing.The casing shall be withdrawn in a controlled manner with the grout level maintained at the top of the element to ensure that the grout completely fills the drill hole. During withdrawal of the casing, the grout level inside the casing shall be monitored to verify that the flow of grout inside the casing is not obstructed.
- For a micropile or portion thereof grouted in an open drill hole in soil without temporary casing, the minimum design diameter of the drill hole shall be verified by a suitable device during grouting.
- For micropiles designed for end bearing, a suitable means shall be employed to verify that the bearing surface is properly cleaned prior to grouting.
- Subsequent micropiles shall not be drilled near elements that have been grouted until the grout has had sufficient time to harden.
- Micropiles shall be grouted as soon as possible after drilling is completed.
- For micropiles designed with a full-length casing, the casing shall be pulled back to the top of the bond zone and reinserted or some other suitable means employed to ensure grout coverage outside the casing.
The requirements of this section address the use of vertical rock and soil anchors in resisting seismic or wind overturning forces resulting in tension on shallow foundations.
The geotechnical report for the Prestressed Rock & Soil Foundation Anchors shall address the following:
- Minimum diameter and minimum spacing for the anchors including consideration of group effects.
- Maximum unbonded length and minimum bonded length of the tendon.
- Maximum recommended anchor tension capacity based upon the soil or rock strength/grout bond and anchor depth/spacing.
- Allowable bond stress at the ground/grout interface and applicable factor of safety for ultimate bond stress.
- Anchor axial tension stiffness recommendations at the anticipated anchor axial tension displacements, when required for structural analysis.
- Minimum grout pressure for installation and post-grout pressure.
- Class I Corrosion Protection is required for all permanent anchors. A minimum of Class II Corrosion Protection is required for temporary anchors in service less than or equal to 2 years.
- Performance test shall be at a minimum of 1.6 times the design loads, but shall not exceed 80 percent of the specified minimum tensile strength of the tendons. There shall be a minimum of two preproduction test anchors. Preproduction test anchors shall be tested to ultimate load or a maximum of 0.80 times the specified minimum tensile strength of the tendon. A creep test is required for all prestressed anchors with greater than 10 kips of lock-off prestressing load.
- Lock-off prestressing load requirements.
- Acceptable drilling methods.
- Geotechnical observation and monitoring requirements.
- Tendons shall be thread-bar anchors conforming to ASTM A722.
- The anchors shall be placed vertical.
- Design loads shall be based upon the load combinations in Section 1605.3.1 and shall not exceed 60 percent of the specified minimum tensile strength of the tendons.
- Ultimate load shall be based upon the lesser of the strength of the superstructure elements, the maximum forces from a fully yielded structural system and forces from the load combinations with overstrength factor in accordance with ASCE 7, Section 12.4.3 and shall not exceed 80 percent of the specified minimum tensile strength of the tendons.
- The anchor shall be designed to fail in grout bond to the soil or rock before pullout of the soil wedge by group effect.
- Foundation design shall incorporate the effect of lock-off loads.
- Design shall account for as-built locations of soil anchors considering all the acceptable construction tolerances.
- Design shall account for both short- and long-term deformation.
- Enforcement agency may require consideration of anchor deformation in evaluating deformation compatibility or building drift where it may be significant.
The requirements of this section shall apply to temporary and permanent earth-retaining shoring using soldier piles and lagging with or without tie-back anchors in soil or rock, only when existing or new facilities are affected. Shoring used as construction means and methods only, which does not affect existing or new facilities, is not regulated by this section and shall satisfy the requirements of the authorities having jurisdiction.
Design, construction, testing, and inspection shall satisfy the requirements of this code except as modified in Sections 1812.2 through 1812.8.
Shoring shall be considered temporary when elements of the shoring will be exposed to site conditions for a period of less than or equal to 2 years, and shall be considered permanent otherwise. Permanent shoring shall account for the increase in lateral soil pressure due to earthquake. At the end of the construction period, the existing and new structures shall not rely on the temporary shoring for support in anyway. Wood components shall not be used for permanent shoring lasting more than 2 years. Wood components of the temporary shoring that may affect the performance of permanent structure shall be removed after the shoring is no longer required.
All components of the shoring shall have corrosion protection or preservative treatment for their expected duration. Wood components of the temporary shoring that will not be removed shall be treated in accordance with AWPA U1 (Commodity Specification A, Use Category 4B and Section 5.2), and shall be identified in accordance with Section 2303.1.9.
Surcharge pressure due to footings, traffic, or other sources shall be considered in the design. If the footing surcharge is located within the semicircular distribution or bulb of earth pressure (when shoring is located close to a footing), lagging shall be designed for lateral earth pressure due to footing surcharge. Soil arching effects may be considered in the design of lagging. Underpinning of the footing may be used in lieu of designing the shoring and lagging for surcharge pressure. Alternatively, continuously contacting drilled pier shafts near the footings shall be permitted. The lateral surcharge design pressure shall be derived using Boussinesq equations modified for the distribution of stresses in an elastic medium due to a uniform, concentrated or line surface load as appropriate and soil arching effects.
The geotechnical report for the earth retaining shoring shall address the following:
- Minimum diameter and minimum spacing for the anchors including consideration of group effects.
- Maximum unbonded length and minimum bonded length of the tie-back anchors.
- Maximum recommended anchor tension capacity based upon the soil or rock strength/grout bond and anchor depth/spacing.
- Allowable bond stress at the ground/grout interface and applicable factor of safety for ultimate bond stress for the anchor. For permanent anchors, a minimum factor of safety of 2.0 shall be applied to the ground soil interface as required by PTI Recommendations for Prestressed Rock and Soil Anchors Section 6.6.
- Minimum grout pressure for installation and post grout pressure for the anchor. The presumptive post grout pressure of 300 psi may be used for all soil types.
- Class I Corrosion Protection is required for all permanent anchors. A minimum of Class II Corrosion Protection is required for temporary anchors in service less than or equal to 2 years.
- Performance test for the anchors shall be at a minimum of two times the design loads and shall not exceed 80 percent of the specified minimum tensile strength of the anchor rod. A creep test is required for all prestressed anchors that are performance tested. All production anchors shall be tested at 150 percent of design loads and shall not be greater than 70 percent of the specified minimum tensile strength of the anchor rod.
- Earth pressure, surcharge pressure, and the seismic increment of earth pressure loading, when applicable.
- Maximum recommended lateral deformation at the top of the soldier pile, at the tie-back anchor locations, and the drilled pier concrete shafts at the lowest grade level.
- Allowable vertical soil bearing pressure, friction resistance, and lateral passive soil resistance for the drilled pier concrete shafts and associated factors of safety for these allowable capacities.
- Soil-pier shaft/pile interaction assumptions and lateral soil stiffness to be used in design for drilled pier concrete shaft or pile lateral loads.
- Acceptable drilling methods.
- Geotechnical observation and monitoring recommendations.
- Tendons shall be thread-bar anchors conforming to ASTM A722.
- Anchor design loads shall be based upon the load combinations in Section 1605.3.1 and shall not exceed 60 percent of the specified minimum tensile strength of the tendons.
- The anchor shall be designed to fail in grout bond to the soil or rock before pullout of the soil wedge.
- Design of shoring system shall account for as-built locations of soil anchors considering all specified construction tolerances in Section 1812.8.
- Design of shoring system shall account for both short- and long-term deformation.
- The geotechnical engineer shall keep a record at the job site of all test loads and total anchor movement, and report their accuracy.
- If a tie-back anchor initially fails the testing requirements, the anchor shall be permitted to be regrouted and retested. If the anchor continues to fail, the followings steps shall be taken:
- The contractor shall determine the cause of failure: (variations of the soil conditions, installation methods, materials, etc.).
- The contractor shall propose a solution to remedy the problem. The proposed solution will need to be reviewed and approved by geotechnical engineer, shoring design engineer, and the building official.
- After a satisfactory test, each anchor shall be locked off in accordance with PTI Recommendations for Prestressed Rock and Soil Anchors Section 8.4.
- The shoring design engineer shall specify design loads for each anchor.
The construction procedure shall address the following:
- Holes drilled for piles/tie-back anchors shall be done without detrimental loss of ground, sloughing or caving of materials and without endangering previously installed shoring members or existing foundations.
- Drilling of earth anchor shafts for tie-backs shall occur when the drill bench reaches 2 to 3 feet below the level of the tie-back pockets.
- Casing or other methods shall be used where necessary to prevent loss of ground and collapse of the hole.
- Drill cuttings from the earth anchor shaft shall be removed prior to anchor installation.
- Unless tremie methods are used, all water and loose materials shall be removed from the holes prior to installing piles/tie-backs.
- Tie-back anchor rods with attached centralizing devices shall be installed into the shaft or through the drill casing. Centralizing devices shall not restrict movement of the grout.
- After lagging installation, voids between lagging and soil shall be backfilled immediately to the full height of lagging.
- The soldier piles shall be placed within specified tolerances in the drilled hole and braced against displacement during grouting. Fill shafts with concrete up to top of footing elevation, rest of the shaft can generally be filled with lean concrete. Excavation for lagging shall not be started until concrete has achieved sufficient strength for all anticipated loads as determined by the shoring design engineer.
- Where boulders and/or cobbles have been identified in the geotechnical reports, the contractor shall be prepared to address boulders and/or cobbles that may be encountered during the drilling of soldier piles and tie-back anchors.
- The grouting equipment shall produce grout free of lumps and indispensed cement. The grouting equipment shall be sized to enable the grout to be pumped in continuous operation. The mixer shall be capable of continuously agitating the grout.
- The quantity of grout and grout pressure shall be recorded. The grout pressure shall be controlled to prevent excessive heave in soils or fracturing rock formations.
- If post-grouting is required, post-grouting operation shall be performed after initial grout has set for 24 hours in the bond length only. Tie-backs shall be grouted over a sufficient length (anchor bond length) to transfer the maximum anchor force to the anchor grout.
- Testing of anchors may be performed after post-grouting operations, provided that grout has reached a strength of 3,000 psi as required by PTI Recommendations for Prestressed Rock and Soil Anchors Section 6.11.
- Anchor rods shall be tensioned straight and true. Excavation directly below the anchors shall not continue before those anchors are tested.
- The shoring design engineer or his designee shall make periodic inspections of the job site for the purpose of observing the installation of the shoring system, testing of tie-back anchors, and monitoring of the survey.
- Testing, inspection, and observation shall be in accordance with testing, inspection and observation requirements approved by the building official. The following activities and materials shall be tested, inspected, or observed by the special inspector and geotechnical engineer:
- Sampling and testing of concrete in soldier pile and tie-back anchor shafts.
- Fabrication of tie-back anchor pockets on soldier beams
- Installation and testing of tie-back anchors.
- Survey monitoring of soldier pile and tie-back load cells.
- Survey monitoring of existing buildings.
- A complete and accurate record of all soldier pile locations, depths, concrete strengths, tie-back locations and lengths, tie-back grout strength, quantity of concrete per pile, quantity of grout per tie-back and applied tie-back loads shall be maintained by the special inspector and geotechnical engineer. The shoring design engineer shall be notified of any unusual conditions encountered during installation.
- Calibration data for each test jack, pressure gauge, and master pressure gauge shall be verified by the special inspector and geotechnical engineer. The calibration tests shall be performed by an independent testing laboratory and within 120 calendar days of the data submitted.
- Monitoring points shall be established at the top and at the anchor heads of selected soldier piles and at intermediate intervals as considered appropriate by the geotechnical engineer.
- Control points shall be established outside the area of influence of the shoring system to ensure the accuracy of the monitoring readings.
- The periodic basis of shoring monitoring, at a minumum, shall be as follows:
- Intitial monitoring shall be performed prior to any excavation.
- Once excavation has begun, the periodic readings shall be taken weekly until excavation reaches the estimated subgrade elevation and the permanent foundation is complete.
- If performance of the shoring is within established guidelines, shoring design engineer may permit the periodic readings to be bi-weekly. Once initiated, bi-weekly readings shall continue until the building slab at ground floor level is completed and capable of transmitting lateral loads to the permanent structure. Thereafter, readings can be monthly.
- Where the building has been designed to resist lateral earth pressures, the periodic monitoring of the soldier piles and adjacent structure can be discontinued once the ground floor diaphragm and subterranean portion of the structure is capable of resisting lateral soil loads and approved by the shoring design engineer, geo-technical engineer, and the building official.
- Additional readings shall be taken when requested by special inspector, shoring design engineer, geotechnical engineer, or the building official.
- Monitoring readings shall be submitted to shoring design engineer, engineer in responsible charge, and the building official within 3 working days after they are conducted. Monitoring readings shall be accurate to within 0.01 feet. Results are to be submitted in tabular form showing at least the intial date of monitoring and reading, current monitoring date and reading and difference between the two readings.
- If the total cummulative horizontal or vertical movement (from start of construction) of the existing buildings reaches 1/2 inch or soldier piles movement reaches 1 inch all excavation activities shall be suspended. The geotechnical and shoring design engineers shall determine the cause of movement, if any, and recommend corrective measures, if necessary, before excavation continues.
- If the total cummulative horizontal or vertical movement (from start of construction) of the existing buildings reaches 3/4 inch or soldier piles movement reaches 11/2 inches all excavation activities shall be suspended until the causes, if any, can be determined. Supplemental shoring shall be devised to eliminate further movement and the building official shall review and approve the supplemental shoring before excavation continues.
- Monitoring of tie-back anchor loads:
- Load cells shall be installed at the tie-back heads adjacent to buildings at maximum interval of 50 feet, with a minimum of one load cell per wall.
- Load cell readings shall be taken once a day during excavation and once a week during the remainder of construction.
- Load cell readings shall be submitted to the geo-technical engineer, shoring design engineer, engineer in responsible charge, and the building official.
- Load cell readings can be terminated once the temporary shoring no longer provides support for the buildings.
- The contractor shall complete a written and photographic log of all existing OSHPD 1, 1R, 2, 4 & 5 structures within 100 feet or three times depth of shoring, prior to construction. A licensed surveyor shall document all existing substantial cracks in adjacent existing structures.
- The contractor shall document the existing condition of wall cracks adjacent to shoring walls prior to start of construction.
- The contractor shall monitor existing walls for movement or cracking that may result from adjacent shoring.
- If excessive movement or visible cracking occurs, the contractor shall stop work and shore/reinforce excavation and contact the shoring design engineer and the building official.
- Monitoring of the existing structure shall be at reasonable intervals as required by the registered design professional, subject to approval of the building official. Monitoring shall be performed by a licensed surveyor and shall consist of vertical and lateral movement of the existing structures. Prior to starting shoring installation a preconstruction meeting shall take place between the contractor, shoring design engineer, surveyor, geotechnical engineer, and the building official to identify monitoring locations on existing buildings.
- If in the opinion of the building official or shoring design engineer, monitoring data indicate excessive movement or other distress, all excavation shall cease until the geotechnical engineer and shoring design engineer investigate the situation and make recommendations for remediation or continuing.
- All reading and measurements shall be submitted to the building official and shoring design engineer
The following tolerances shall be specified on the construction documents.
- Soldier piles:
- Horizontal and vertical construction tolerances for the soldier pile locations.
- Soldier pile plumbness requirements (angle with vertical line).
- Tie-back anchors:
- Allowable deviation of anchor projected angle from specified vertical and horizontal design projected angle.
- Anchor clearance to the existing/new utilities and structures.
This section shall apply to Vibro Stone Columns (VSCs) for ground improvement using unbounded aggregate materials. Vibro stone column provisions in this section are intended to increase bearing capacity, reduce settlements, and mitigate liquefaction for shallow foundations. These requirements shall not be used for grouted or bonded stone columns, ground improvement for deep foundation elements, or changing site class. VSCs shall not be considered as a deep foundation element.
Ground improvement shall be installed under the entire building/structure footprint and not under isolated foundation elements only.
Design, construction, testing, and inspection shall satisfy the requirements of this code except as modified in Sections 1813.2 through 1813.5.
The geotechnical report shall specify vibro stone column requirements to ensure uniformity in total and differential immediate settlement, long-term settlement, and earthquake-induced settlement. The report shall address the following:
- Soil compaction shall be sufficient to mitigate potential for liquefaction as described in California Geological Survey (CGS) Special Publication 117A (SP-117A): Guidelines for Evaluating and Mitigating Seismic Hazard in California.
- The area replacement ratio for the compaction elements and the basis of its determination shall be explained. Minimum factor of safety for soil compaction shall be in accordance with SP-117A.
- The depth of soil compaction elements and extent beyond the footprint of structures/foundation shall be defined. Extent beyond the foundation shall be half the depth of the VSCs with a minimum of 10' or an approved alternative.
- The minimum diameter and maximum spacing of soil compaction elements shall be specified. VSCs shall not be less than 2 feet in diameter and center to center spacing shall not exceed 8 feet.
- The modulus of subgrade reactions for shallow foundations shall account for the presence of compaction elements.
- The modulus of subgrade reactions, long-term settlement, and post-earthquake settlement shall be specified along with expected total and differential settlements for design.
- The acceptance criteria for friction cone and piezocone penetration testing in accordance with ASTM D5778 complemented by a standard penetration test (SPT) in accordance with ASTM D1586, if necessary, to verify soil improvement shall be specified.
- The requirements for special inspection and observation by the geotechnical engineer shall be specified.
- A Final Verified Report (FVR) documenting the installation of the ground improvement system and confirming that the ground improvement acceptance criteria have been met shall be prepared by the geotechnical engineer and submitted to the enforcement agency for review and approval.
VSCs under the shallow foundation shall be located symmetrically around the centroid of the footing or load, and:
- There shall be a minimum of four stone columns under each isolated or continuous/combined footing or an approved equivalent.
- The VSCs or deep foundation elements shall not be used to resist tension or overturning uplift from the shallow foundations.
- The foundation design for the shallow foundation shall consider the increased vertical stiffness of the VSCs as point supports for analysis, unless it is substantiated that the installation of the VSCs results in improvement of the surrounding soils such that the modulus of subgrade reaction, long-term settlement, and post-earthquake settlement can be considered uniform throughout.
VSCs shall be installed with vibratory probes. Vertical columns of compacted unbounded aggregate shall be formed through the soils to be improved by adding gravel near the tip of the vibrator and progressively raising and re-penetrating the vibrator, which will results in the gravel being pushed into the surrounding soil.
Gravel aggregate for VSCs shall be well graded with a maximum size of 6 inches and not more than 10 percent smaller than 3/8 inch after compaction.
Construction documents for VSCs, at a minimum, shall include the following:
- Size, depth, and location of VSCs.
- The extent of soil improvements along with building/structure foundation outlines.
- Field verification requirements and acceptance criteria using CPT/SPT.
- The locations where CPT/SPT shall be performed.
- A Testing, Inspection and Observation (TIO) program indicating the inspection and observation required for the VSCs.