Effects of Surrounding Soil Stiffness and Shaft Length in the Impact-Echo Test of Drilled Shaft

Abstract

The objective of this work was to present the criteria in which the impact-echo test can be applied. Major parameters that affected the success of the impact-echo test were shaft-to-soil stiffness ratio (Ec/Es) and length-to-diameter ratio of shaft (L/D). Three-dimensional (3-D) axisymmetric finite element models were used to simulate the testing. Extensive parametric studies were performed numerically and experimentally, and the velocity time histories were obtained. The effects of the relative stiffness of the surrounding soil to that of the drilled shaft and the shaft embedded depth were investigated. It was found that impact-echo test can be applied to the drilled shaft if the shaft-to-soil stiffness ratio (Ec/Es) is more than 77, and the length-to-diameter ratio of shaft (L/D) is less than 27.