Evaluation of Surface Wave Method for Assessment of Heterogeneous Improved Ground

Abstract

Soft ground is often improved to increase strength and stiffness by methods such as jet grouting and stone column which result in heterogeneous ground with improved columns. Experimental methods (Standard Penetration Test, sampling and laboratory testing, etc.) used to assess such ground improvement are subjected to several limitations such as small sampling volume, time-consuming, and cost ineffectiveness. the seismic surface wave method (i.e. multi-station analysis of surface wave, MASW) can non-destructively measure shear-wave velocity depth profile over wider lateral sampling range. It appears to be a good alternative or complement for efficient evaluation of overall quality of improved ground. However, current surface wave method is essentially a 1-D method assuming horizontally-layered medium. What MASW measures in the highly heterogeneous improved ground remains to be investigated. Field testings before and after ground improvements were performed to evaluate the feasibility of MASW method in the heterogeneous ground with improved columns. the performance and effect of lateral sampling of the surface wave testing were investigated by field testings with different survey line locations relative to the improved columns. the MASW testing in the heterogeneous improved ground was numerically modeled by finite difference method. Parametric studies were performed to investigate how the heterogeneous shear wave velocities were homogenized by the surface wave measurement. the engineering Information that can be extracted from the improvement rate of shear wave velocity obtained by surface wave testing is discussed based on the field experience and numerical Investigations.