NONLINEAR-ANALYSIS OF SETTLEMENT AND LOAD DISTRIBUTION IN PILE GROUPS

Settlement of and load distribution in pile groups under vertical and centered static loads are analyzed. The analytical method incorporates the fact that shaft-load over point-load ratios vary throughout loading, thus coupling the effects of shaft-loads and point-loads on group settlement calculations. Other available methods uncouple shaft-loads and point-loads using simplifying assumptions which are not always in agreement with observed pile group behavior. It is assumed that the shaft-load of piles in groups increases monotonically with loading according to a nonlinear relationship. This can be defined from results of a reference pile load test with point-load measurement, for example. It is also assumed that the ultimate shaft-load develops before the ultimate point-load. These assumptions, which are in general agreement with observed behavior, are used along with settlement influence factors and settlement interaction factors numerically generated for a semi-infinite, homogeneous, linear, elastic, isotropic halfspace. The result is a set of nonlinear simultaneous algebraic equations which are solved using the modified Newton-Raphson iterative method to yield the group settlement, as well as point-loads and shaft-loads for each pile in the group. The numerical procedure used to solve these equations is outlined and an analysis is made of the necessary conditions for convergence when the equations are weakly nonlinear. An example is provided to illustrate how the method compares with two other methods reported in the literature. It is observed that the proposed method has the potential to accurately simulate the nonlinear load versus settlement behavior. © 1990.