UpCodes logo
// CODE SNIPPET

Section 3106F Geotechnical Hazards and Foundations

Go To Full Code Chapter
TABLE 31F-6-1
SITE CLASS SOIL PROFILE AVERAGE VALUES FOR TOP 100 FEET OF SOIL PROFILE3
Shear Wave Velocity,
VS [ft/sec]
Standard Penetration Test,
SPT [blows/ft]
Undrained Shear Strength,
SU [psf]
A Hard Rock > 5,000    
B Rock 2,500 to 5,000    
C Very Stiff/Very Dense Soil and Soft Rock 1,200 to 2,500 > 50 > 2,000
D Soft/Dense Soil Profile 600 to 1,200 15 to 50 1,000 to 2,000
E1, 2 Soft/Loose Soil Profile < 600 < 15 < 1,000
F Defined in Section 3106F.2.1
  1. Site Class E also includes any soil profile with more than 10 feet of soft clay (defined as a soil with a plasticity index, PI > 20, water content > 40 percent and Su < 500 psf).
  2. The plasticity index, P1, and the moisture content shall be determined in accordance with ASTM D4318 [6.1] and ASTM D2216 [6.2], respectively.
  3. Conversion of CPT data to estimate equivalent Vs, SPT blow count, or Su is allowed.
FIGURE 31F-6-1
AXIAL SOIL SPRINGS [6.8]
FIGURE 31F-6-2
SLIDING LAYER MODEL [6.8]
3106F.1 General
3106F.1.1 Purpose
This section provides minimum standards for analyses and evaluation of geotechnical hazards and foundations under static and seismic conditions.
3106F.1.2 Applicability
The requirements provided herein apply to all new and existing MOTs.
3106F.1.3 Loading
The loading for geotechnical hazard assessment and foundation analyses under static and seismic conditions is provided in Sections 3103F and 3104F.
3106F.2 Site Characterization
Site characterization shall be based on site-specific geotechnical information. If existing information is used, the geotechnical engineer of record shall provide adequate justification.
3106F.2.1 Site Classes
Each MOT shall be assigned at least one site class. Site Classes A, B, C, D and E are defined in Table 31F-6-1, and Site Class F is defined by any of the following:
  1. Soils vulnerable to significant potential loss of stiffness, strength and/or volume under seismic loading due to liquefiable soils, quick and highly sensitive clays and/or collapsible weakly cemented soils.
  2. Peats and/or highly organic clays, where the thickness of peat or highly organic clay exceeds 10 feet.
  3. Very high plasticity clays with a plasticity index (PI) greater than 75, where the thickness of clay exceeds 25 feet.
  4. Very thick soft/medium stiff clays with undrained shear strength less than 1,000 psf, where the thickness of clay exceeds 120 feet.
3106F.2.2 Site-Specific Information
  1. Site-specific investigations shall include adequate borings and/or cone penetration tests (CPTs) and other appropriate field methods, to enable the determination of geotechnical parameters.
  2. Adequate coverage of subsurface data, both horizontally and vertically, shall be obtained to develop geotechnical parameters.
  3. Exploration shall be deep enough to characterize subsurface materials that are affected by embankment behavior and shall extend to depth of at least 20 feet below the deepest foundation depth.
  4. During field exploration, particular attention shall be given to the presence of continuous low-strength layers or thin soil layers that could liquefy or weaken during the design earthquake shaking.
  5. CPTs provide continuous subsurface profile and shall be used to complement exploratory borings. When CPTs are performed, at least one boring shall be performed next to one of the CPT soundings to check that the CPT-soil behavior type interpretations are reasonable for the site. Any difference between CPT interpretation and subsurface condition obtained from borings shall be reconciled.
  6. Quantitative site soil stratigraphy is required to a depth of 100 feet for assigning a site class (see Table 31F-6-1).
  7. Laboratory tests may be necessary to supplement the borings and insitu field tests.
3106F.3 Seismic Loads for Geotechnical Evaluations
Section 3103F.4 defines the earthquake loads to be used for structural and geotechnical evaluations in terms of design Peak Ground Accelerations (PGA), spectral accelerations and design earthquake magnitude. Values used for analyses are based on Probabilistic Seismic Hazard Analyses (PSHA) using two levels of seismic performance criteria (Section 3104F.2.1 and Table 31F-4-1).
3106F.4 Liquefaction Potential
The liquefaction potential of the soils in the immediate vicinity of or beneath each MOT, and associated slopes, embankments or rock dikes shall be evaluated for the PGAs associated with seismic performance Levels 1 and 2. Liquefaction potential evaluation should follow the procedures outlined in NCEER report [6.3], SCEC [6.4] and CGS Special Publication 117A [6.5].
If liquefaction is shown to be initiated in the above evaluations, the particular liquefiable strata and their thicknesses shall be clearly shown on site profiles. Resulting hazards associated with liquefaction shall be addressed including translational or rotational deformations of slopes or embankment systems and post liquefaction settlement of slopes or embankment systems and underlying foundation soils, as noted below. If such analyses indicate the potential for partial or gross (flow) failure of a slope or embankment, adequate evaluations shall be performed to confirm such a condition exists, together with analyses to evaluate potential slope displacements (lateral spreads). In these situations and for projects where more detailed numerical analyses are performed, a peer review (see Section 3101F.8.2) may be required.
3106F.5 Slope or Embankment Stability and Seismically Induced Lateral Spreading
Slope or embankment stability related to the MOT facility, shall be evaluated for static and seismic loading conditions.
3106F.5.1 Static Slope Stability
Static stability analysis using conventional limit equilibrium methods shall be performed for site related slope or embankment systems. Live load surcharge shall be considered in analyses based on project-specific information. The long-term static factor of safety of the slope or embankment shall not be less than 1.5.
3106F.5.2 Pseudo-Static Seismic Slope Stability
Pseudo-static seismic slope or embankment stability analyses shall be performed to estimate the horizontal yield acceleration for the slope for the Level 1 and Level 2 earthquakes. During the seismic event, appropriate live load surcharge shall be considered.
If liquefaction and/or strength loss of the site soils is likely, the following shall be used in the analyses, as appropriate:
  1. Residual strength of liquefied soils
  2. Strengths compatible with the pore-pressure generation of potentially liquefiable soils
  3. Potential strength reduction of clays
The residual strength of liquefied soils shall be estimated using guidelines outlined in SCEC [6.4] or other appropriate documents as noted in CGS Special Publication 117A [6.5].
Pseudo-static analysis shall be performed without considering the presence of the foundation system. Using a horizontal seismic coefficient of one-half of the PGA, if the estimated factor of safety is greater than or equal to 1.1, then no further evaluation of lateral spreading or kinematic loading from lateral spreading is required.
3106F.5.3 Post-Earthquake Static Slope Stability
The static factor of safety immediately following a design earthquake event shall not be less than 1.1 when any of the following are used in static stability analysis:
  1. Post-earthquake residual strength of liquefied soils
  2. Strengths compatible with the pore-pressure generation of potentially liquefiable soils
  3. Potential strength reduction of clays
3106F.5.4 Lateral Spreading — Free Field
The earthquake—induced lateral deformations of the slope or embankment and associated foundations soils shall be determined for the Level 1 and Level 2 earthquakes using the associated PGA at the ground surface (not modified for liquefaction). If liquefaction and/or strength loss of the site soils is likely, the following shall be used in the analyses, as appropriate:
  1. Residual strength of liquefied soils
  2. Strengths compatible with the pore-pressure generation of potentially liquefiable soils
  3. Potential strength reduction of clays
The presence of the foundation system shall not be included in the "free field" evaluations.
Initial lateral spread estimates shall be made using the Newmark displacement approach documented in NCHRP Report 611 [6.6] or other appropriate but similar procedures.
3106F.6 Seismically Induced Settlement
Seismically induced settlement shall be evaluated. Based on guidelines outlined in SCEC [6.4] or other appropriate documents such as CGS Special Publication 117A [6.5]. If seismically induced settlement is anticipated, the resulting design impacts shall be considered, including the potential development of downdrag loads on piles.
3106F.7 Earth Pressures
Both static and seismic earth pressures acting on MOT structures shall be evaluated.
3106F.7.1 Earth Pressures Under Static Loading
The effect of static active earth pressures on structures resulting from static loading of backfill soils shall be considered where appropriate. Backfill sloping configuration, if applicable, and backland loading conditions shall be considered in the evaluations. The loading considerations shall be based on project-specific information. The earth pressures under static loading should be based on guidelines outlined in NAVFAC DM7-02 [6.7] or other appropriate documents.
3106F.7.2 Earth Pressures Under Seismic Loading
The effect of earth pressures on structures resulting from seismic loading of backfill soils, including the effect of porewater pressure build-up in the backfill, shall be considered. The seismic coefficients used for this analysis shall be based on the Level 1 and Level 2 earthquake PGA values.
Evaluation of earth pressures under seismic loading, should be based on NCHRP Report 611 [6.6] or other appropriate methods.
3106F.8 Pile Axial Behavior
3106F.8.1 Axial Pile Capacity
Axial geotechnical capacity of piles under static loading shall be evaluated using guidelines for estimating axial pile capacities provided in POLB WDC [6.8] or other appropriate documents. A minimum factor of safety of 2.0 shall be achieved on the ultimate capacity of the pile using appropriate MOT loading.
If liquefaction or seismically-induced settlement is anticipated, the ultimate axial geotechnical capacity of piles under seismic conditions shall be evaluated for the effects of liquefaction and/or downdrag forces on the pile. The ultimate geotechnical capacity of the pile during liquefaction shall be determined on the basis of the residual strength of the soil for those layers where the factor of safety for liquefaction is determined to be less than 1.0.
When seismically-induced settlements are predicted to occur during design earthquakes, the downdrag loads shall be computed, and the combination of downdrag load and static load determined. Only the tip resistance of the pile and the side friction resistance below the lowest layer contributing to the downdrag shall be used in the capacity evaluation. The ultimate axial geotechnical capacity of the pile shall not be less than the combination of the seismically induced downdrag force and the maximum static load.
3106F.8.2 Axial Springs for Piles
The geotechnical analyst (see Section 3102F.3.4.8) shall coordinate with the structural analyst (see Section 3102F.3.4.4) and develop axial springs (T-z) for piles. The T-z springs may be developed either at the top or at the tip of the pile (see Figure 31F-6-1). If the springs are developed at the pile tip, the tip shall include both the friction resistance along the pile (i.e., side springs [t-z]) and tip resistance at the pile tip (i.e. tip springs [q-w]), as illustrated in Figure 31F-6-1. If T-z springs are developed at the pile top, the appropriate elastic shortening of the pile shall be included in the springs. Linear or nonlinear springs may be developed if requested by the structural analyst.
Due to the uncertainties associated with the development of axial springs, such as the axial soil capacities, load distributions along the piles and simplified spring stiffnesses, both upper-bound and lower-bound limits shall be estimated and utilized in the analyses.
3106F.9 Soil Springs for Lateral Pile Loading
For design of piles under loading associated with the inertial response of the superstructure, level-ground inelastic lateral springs (p-y) shall be developed. The lateral springs within the shallow portion of the piles (generally within 10 pile diameters below the ground surface) tend to dominate the inertial behavior. Geotechnical parameters for developing lateral soil springs shall follow guidelines provided in API RP 2A-WSD [6.9] or other appropriate documents.
Due to uncertainties associated with the development of p-y curves for dike structures, upper-bound and lower-bound p-y springs shall be developed for use in superstructure inertial response analyses.
3106F.10 Soil-Pile Interaction
Two separate loading conditions for the piles shall be considered:
  1. Inertial loading under seismic conditions
  2. Kinematic loading from lateral ground spreading
Inertial loading is associated with earthquake-induced lateral loading on a structure, while kinematic loading refers to loading on foundation piles from earthquake induced lateral deformations of the slope/embankment/dike system. Simultaneous application of these loading conditions shall be evaluated with due consideration of the phasing and locations of these loads on foundation elements. The foundation shall be designed such that the structural performance is acceptable when subjected to both inertial and kinematic loadings.
3106F.10.1 Inertial Loading Under Seismic Conditions
The lateral soil springs shall be used in inertial loading response analyses. The evaluation of inertial loading can be performed by ignoring potential slope/embankment/dike system deformations (i.e., one end of the lateral soil spring at a given depth is attached to the corresponding pile node and the other end is assumed fixed).
See More

Related Code Sections

Section 3106F [SLC] Marine Oil Terminals, Geotechnical Hazards and Foundations
This section provides minimum standards for analyses and evaluation of geotechnical hazards and foundations under static and seismic conditions ...
Section 3106F [SLC] Marine Oil Terminals, Geotechnical Hazards and Foundations
section provides minimum standards for analyses and evaluation of geotechnical hazards and foundations under static ...
Section 3106F [SLC] Marine Oil Terminals, Geotechnical Hazards and Foundations
This section provides minimum standards for analyses and evaluation of geotechnical hazards and foundations under static and seismic conditions ...
3106F.10 [SLC] Marine Oil Terminals, Soil-Pile Interaction
on foundation piles from earthquake induced lateral deformations of the slope/embankment/dike system. Simultaneous application of these loading conditions ...