Non-Destructive Testing Of Ground Strength Using The Sasw-Method

The shear modulus of soils and rock is an important parameter for estimating the mechanical<br>behaviour of these materials under many different types of loading. A relatively little used but<br>promising geophysical method for assessing variation in shear wave velocity and shear modulus<br>with depth is Spectral Analysis of Surface Waves (SASW). The result of an SASW-measurement<br>is a dispersion curve of Rayleigh wave velocity versus wavelength. A profile of shear wave<br>velocity and shear modulus with depth can then be derived from the dispersion curve using<br>simple approximate techniques or forward modelling. Contrary to seismic refraction methods,<br>SASW can be used to detect low-velocity layers.<br>Two case studies that show the capability of the SASW-technique for non-destructive evaluation<br>of ground strength are presented here. The first concerns a railway bridge in southern Sweden.<br>The SASW-method was used for investigating the ground strength under the bridge pillars<br>before constructing the bridge. The second case study concerns assessment of ground stability<br>improvement at a construction site outside Copenhagen. At the latter study it was found that<br>forward modelling was necessary in order to determine an accurate profile of shear modulus with<br>depth.