| R 65,T 5In this study, the factors influencing the response of a drilled shaft to load are evaluated, and rational and consistent criteria are developed for the proper conduct and interpretation of load tests for axial compression and uplift, lateral and moment, torsion, and combined loading.;It is shown that for soils which do not exhibit significant creep displacements, the quick loading procedure can be used without influencing the test results. If significant creep displacements are anticipated, the equilibrium procedure should be used.;Existing interpretation methods are reviewed, and new methods are described for interpreting the load test results. For axial compression tests, the load corresponding to a displacement equal to 4 percent of the diameter gave consistent results and fulfilled most of the requirements for a satisfactory interpretation method. For axial uplift, the load corresponding to a displacement of 0.5 in (12.5 mm) was shown to give consistent results. The method proposed for lateral test results requires that the slope of the butt of the shaft be measured along with its lateral displacement. With this new method, the failure mode of the shaft also can be evaluated. Because the torque-twist curve obtained from a torsion test is similar to the axial compression load-displacement curve, procedures recommended for axial compression tests can be used to interpret torsion test results. However, enough data were not available to recommend a twist level required to cause torsion "failure" of the foundation. For combined loading, the interpretation methods recommended for the individual loading modes can be used to evaluate the "failure" of the foundation.;The influence of loading rate, equipment, and instrumentation on the accuracy of the load test results is evaluated, and the relevance of a thorough geotechnical investigation in determining the proper loading rate, equipment, instrumentation, test result interpretation, and extrapolation to other sites is demonstrated. |
