Geotechnical Engineering Circular No. 9 Design, Analysis, and Testing of Laterally Loaded Deep Foundations that Support Transportation Facilities
Figure 12-3: Arrangement for two-way lateral loading (a) compression (b) tension
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| Figure 12-3: Arrangement for two-way lateral loading (a) compression (b) tension. Cyclic lateral load tests are sometimes performed to investigate the load-displacement response, when such issues are relevant to design, such as earthquake loads and wave impact loading. However, although reciprocating jacks allow load reversals, the frequency of load cycles cannot match the ground motions experienced during earthquakes. 184 When soil liquefaction is a concern, research tests have been performed in conjunction with blasting to liquefy the ground adjacent to the pile/shaft during the test. Rollins et al. (2001) reported the results of lateral load tests on deep foundations during blast induced liquefaction of granular soils on Treasure Island in San Francisco Bay, California, near the National Geotechnical Experimentation Site (NGES). Static lateral load tests should be performed in accordance with ASTM D Standard Test Method for Deep Foundations under Lateral Load this test standard should be referenced for details on requirements of the test foundation preparation, apparatus for applying and measuring loads, apparatus for measuring movement, test procedures, equipment calibration, safety requirements, and items to be addressed in a lateral load test report. This test standard is recommended in the absence of owner specific requirements. The standard shows examples of various test setup arrangements for both one- way and two-way loading, using a variety of reaction systems. The standard also provides examples of the lateral loading apparatus, including conventional hydraulic cylinder ram jacks, center-hole jacks, and single line and multi-line winch setups. Arrangements fora fixed head condition are also described. ASTM D has 8 loading schedules to choose from, denoted as Procedures A through H. Procedure A recommends a loading schedule that consists of 1) load increments to a maximum of 200 percent of the design lateral load, followed by 4 decrements of load. Hold periods vary from 10 minutes up to 60 minutes depending on the particular load increment. Assuming the test pile or shaft is not a production pile, then it is preferred that the loading increase until the element deflects enough that the geotechnical resistance at the ultimate Limit State is approached. The test standard has provisions for excess loading stages beyond the standard loading schedule, up to a maximum of 250 percent of the design load in what is termed Procedure B. However, the development of plastic hinges in the pile or drilled shaft should be avoided. If cyclic loading is required, Procedure C should be followed. A further option provided in the standard is Procedure D, for surge loading that involves multiple loading cycles at any specified load increment. Surge loading can be implemented during the standard loading schedule or following completion of the standard schedule of loading. If reverse loading is required, then Procedure E is followed whereby loads are applied either by pushing, then pulling, or vice versa. Reciprocal loading is provided for under Procedure F. The lateral load increment is applied in one direction and then the other direction fora specified number of cycles. In Procedure G, the testis performed until a specified lateral displacement is measured. Last, Procedure His for combined loading in which an axial load is applied to the test pile or shaft first, and then the lateral load is applied with the axial load held constant during the test. Download 6.03 Mb. Share with your friends:
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