Application of surface wave method in assessment of ground modification with improvement columns

Surface wave testing is considered a promising method for assessing average property and actual area replacement ratio of ground modification with improvement columns, owing to its non-destructive nature and large sampling range. However, the surface wave method is essentially a 1-D method assuming horizontally-layered medium. What it measures in highly heterogeneous improved ground remains to be investigated. This study aimed at evaluating the feasibility of surface wave method in the heterogeneous ground with improved columns, and investigating the homogenization of shear wave velocity and the lateral sampling range. Field tests on a jet grouted construction site showed that the surface wave method worked well in such heterogeneous grounds and yielded a site-representative shear wave velocity profile regardless of the survey location. This is attributed to the survey condition where the wavelength is greater than the spacing of grout columns. 1-D analytical models and 2-D numerical simulations were conducted to investigate the quantitative relation between construction parameters and the percentage increase of shear wave velocity after ground improvement. A quantitative approach to estimate the area replacement ratio and overall quality of improvement columns by surface wave testing is proposed.