Determination of Sandy Subsoil Stiffness on the Basis of Surface Vibration Measurement

The main aim of the study is an attempt of determination of the stiffness modulus of sandy subsoil based on analysis of data recorded during the measurements of vibrations conducted on the surface of the ground. The procedure proposed in the article is similar, to some extent, to the method of Spectral Analysis of Surface Waves (SASW). The main difference between the proposed way and the SASW method is application of a different type of a ground load, the use of accelerometers instead of geophones and application an backward analysis in place of the most frequently used in geophysics factored wavelength method. Field tests of acceleration of vibrations were carried out at measuring points located at a distance of 5 m and 10 m from the source of vibration. The Light Falling Weight Deflectometer (LFWD) was the source of vibration. Measurements of vibration were executed using measuring system produced by Siemens (LMS Scadas Recorder). The determination of the subsoil stiffness was made on the basis of obtained results in two ways. The first simple way was based on measuring the time of movement of the Rayleigh wave between the measuring points. The second way was to use the own author's computational program and backward analysis. The program based on the Finite Difference Method (FDM) enabled the description of wave propagation in the ground under the impact load. The proposed method allowed the determination of the average values of stiffness modulus of subsoil G and E. This method can be useful for analysis of the level of vibrations transmitted to the foundations of buildings. They can also be the basis of determination of the necessary stiffness parameters for soil-structure interaction analysis in various problems of dynamics of structures. It can be used to evaluate the stiffness of soil in road embankments. The method is nondestructive (needs no boreholes) and can be fully automatized.