ESTIMATION OF SUBGRADE REACTION COEFFICIENT FOR HORIZONTALLY LOADED PILES BY STATISTICAL ANALYSES

摘要

The purpose of the present study is to estimate horizontal subgrade reaction coefficient (k_h) of piles from SPT N-value that is required to design piles against horizontal loading. This information is much demanded recently due to the introduction of the limit state design of pile foundations where quantified uncertainty in the prediction of pile behavior is required. For this purpose 52 horizontal pile loading test results were collected from literatures and reports, which were compiled in a database. The actual number of test results put to the statistical analyses was 38 cases with pile top displacement and 21 cases with bending moment measurements along a pile. The statistical analyses were carried out in the two folds; First, the inverse analysis procedure was applied to each loading test result to obtain the coefficients in different soil layers. Then the obtained coefficient values were related to observed SPT N-values of the layers by the regression analysis. The pronounced feature of the regression analysis employed in this study is that it takes into account the magnitude of estimation uncertainty as well as the correlation structure of estimated k_h for every pile automatically. The mean value of k_h obtained from the recommended equation in this study gives very similar results to those of the major design equations used in Japan. The uncertainties associated with the recommended equation are presented, which are intended to be used in a reliability analysis of horizontally loaded piles.