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1808.4.1 Compressive Load Tests
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Where load tests are required, at least one test shall be performed in each area of the foundation site within which the subsurface soil conditions are "substantially similar" in character, as determined by the engineer, and at least one test shall be performed for each pile type for the entire foundation installation of the building or group of buildings on a site occupying a total area of 5,000 square feet (465 m2) or less. Where load tests are required, at least two load tests shall be performed for a site having a footprint between 5,000 square feet (465 m2) and 30,000 square feet (2787 m2), and one additional load test shall be performed for each 20,000 square feet (1860 m2) of added footprint area. For conditions where multiple pile types or capacities are used, refer to Section 1808.2.5.
Where installed pile capacities are in doubt, the piles are considered non-conforming by the engineer, or as required by the commissioner, additional piles shall be load tested to establish the allowable capacity. For friction piles where the actual production pile lengths vary more than 25 percent from that of the test pile, the engineer shall determine if additional load tests are required to establish the allowable pile capacity. The number of additional load tests shall be determined by the engineer or commissioner.
Compressive load tests shall be conducted in accordance with ASTM D 1143 standard procedures and the following conditions:
- Dial extensometer gages shall provide readings to the nearest 0.001 inch (0.025 mm). Electrical transducers may be used to make settlement observations, provided that backup measurements are made utilizing dial extensometers as described herein at sufficient times to validate the transducer readings.
- If the allowable axial compressive load is less than or equal to the Basic Maximum Allowable Pile Load in Table 1808.4.1.3, the total test load shall remain in place for a minimum of 12 hours, and shall be held until the average rate of settlement as measured over a 12-hour period does not exceed 0.001 inches (0.025 mm) per hour. The total load shall be removed in decrements not exceeding 25 percent of the total load at 1 hour intervals or longer. For cases where the allowable pile load is greater than the values prescribed in Table 1808.4.1.3, refer to Section 1808.4.1.5.
- In addition to observations required by ASTM D 1143, settlement observations shall be performed 24 hours after the entire test load has been removed.
Exception: A static load test for drilled piles using an embedding load transfer mechanism shall be considered acceptable, provided that the test is performed in general accordance with ASTM D 1143 — Quick Load Test Method. The pile shall be suitably instrumented to evaluate the load transfer through soil or rock at multiple locations along the shaft.
- Any temporary supporting capacity that the soil might provide to the pile during a load test, but which would be dissipated with time, shall be eliminated by casing off or by other suitable means, such as increasing the total test load to account for such temporary capacity.
|TYPE OF PILE||MAXIMUM ALLOWABLE PILE LOAD (TONS)|
|Caisson Piles||No upper limit|
|Open-end pipe (or tube) piles bearing on rock of Class 1a, 1b, or 1c||18-in O.D. and greater||250|
|14-in to 18-in O.D.||200|
|12-in to 14-in O.D.||150|
|10-in to 12-in O.D.||100|
|8-in to 10-in O.D.||60|
|Closed-end pipe (or tube) piles, H-piles, cast-in-place concrete, enlarged base piles, and precast concrete piles bearing on rock of Class 1a, 1b, or 1c||150|
|Piles (other than timber or helical piles) bearing on soft rock of Class 1d||80|
|Piles (other than timber or helical piles) that receive their principal support other than by direct bearing on rock of Class 1a through 1d||75|
|Timber piles bearing on rock of Class 1a through 1d||25|
|Timber piles bearing in suitable soils|| 40 tons maximum permissible |
with load test, 30 tons maximum
without load test.
|Helical piles||30 tons maximum permissible|
For SI: 1 ton = 907.18 kg.
High strain, dynamic compressive test methods performed in accordance with ASTM D 4945 shall be permitted to be used where three or more load tests are required and subject to the approval of the commissioner. In such case, at least one high strain dynamic test shall be performed as a calibration on a static load tested pile or nearby pile driven to comparable resistance. No more than one-half of the required number of load tests may be performed by high strain dynamic methods. High strain dynamic tests shall be performed under the supervision of an engineer experienced in the methods used. The number of high strain dynamic tests shall be at least twice the number of replaced static load tests.
The allowable pile load shall be the lesser of the two values computed as follows:
- Fifty percent of the applied load causing a net settlement of the pile of not more than 1/100 of 1 inch per ton (0.25 mm per 8.9 kN) of applied load. Net settlement in this paragraph is defined as gross settlement due to the total test load minus the rebound after removing 100 percent of the test load.
- Fifty percent of the applied load causing a net settlement of the pile of 3/4 inch (19 mm). Net settlement in this paragraph is defined as the gross settlement due to the total test load less the amount of elastic shortening in the pile section due to total test load. The elastic shortening shall be calculated as if the pile is designed as an end-bearing pile or as a friction pile. Alternatively, the net settlement may be measured directly using a telltale or other suitable instrumentation.
The basic maximum allowable pile loads tabulated in Table 1808.4.1.3 may be exceeded where a higher value can be substantiated on the basis of load tests and analysis, except for the loads for timber and helical piles. The provisions of Section 1808.4.1 shall be supplemented, as follows: the final load increment shall remain in place for a total of not less than 24 hours; single test piles shall be subjected to cyclical loading or suitably instrumented with telltales and strain gauges so that the movements of the pile tip and butt may be independently determined and load transfer to the soil evaluated. A complete record demonstrating satisfactory performance of the test shall be submitted to the commissioner.
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