Pressuremeter design method for single piles subjected to static lateral load

Abstract

A thorough review of the literature regarding design methods for lateral load behavior of foundation piles has been made. The most popular and versatile design technique is solution of the governing differential equation for the pile. The solution is obtained by the finite difference scheme using a high speed digital computer. Some dissatisfaction is evident in the literature with the existing techniques available to describe the nonlinear spring representing the soil surrounding the pile which is expressed as a P-y curve. The theoretical and experimental basis for the soil P-y curves is presented, and the relationship between the lateral reaction mechanisms of pile and pressuremeter is explored in both elasticity and plasticity. The P-y curve is shown to consist of two components: a frontal reaction, and a side shear reaction. It is shown that interpretation of a prebored pressuremeter test can measure both components. Using the theoretical stress distributions around a translating pile, a new method for the development of a lateral load P-y curve, based on plane strain, is proposed. The reduction in mobilized soil reaction close to the free ground surface, termed the critical depth effect, is known to be of paramount importance for a laterally loaded pile. Based on interpretation of field instrumented pile test results, a new method of accounting for the pile critical depth which incorporates relative soil/pile rigidity is proposed. From a small strain finite element study of the expansion of a cylindrical cavity the critical depth effect for a pressuremeter is examined. A new approach to determine the pressuremeter critical depth is recommended. A series of model pile and pressuremeter tests conducted under laboratory conditions confirmed the validity of the proposed P-y curve construction procedure. Two proposed tentative methods an Initial Criterion and a Reload Criterion, were successfully applied to fourteen full scale laterally loaded piles at nine field sites where pressuremeter tests were conducted. Based on the results from the tentative methods a final method is proposed to construct static lateral load P-y curves from a prebored pressuremeter test. A computer program, PYGEN, has been written to accomplish this task. Recommendations are given concerning the application of the method and pressuremeter testing procedures.