Application of multichannel analysis of surface wave to shallow site investigation for subsoil in Thailand

Abstract

The multichannel analysis of surface wave method (MASWM) is a nondestructive test recently developed for subsoil characterization. By conducting the test on ground surface, the shear wave velocity which is a necessary parameter for dynamic analysis, can be easily attained. In this study, the tests have conducted at seven sites in Thailand along with the seismic downhole test, searching for the validity and proper inversion algorithm as well as the best practice for testing. The process consists of three sequences which are the field data collection, the transformation by the Two Dimensional Fast Fourier Transform (2D FFT), and the inversion to shear wave velocity profile. Afterward, the obtained shear wave velocity profiles are investigated by comparing with the predictions by other methods; namely those from seismic downhole tests, boring reports, and Seismic Cone Penetration Test (SCPT). It is found that the λ/3 inversion algorithm offers the predictions that are consistent with other methods. Therefore, it is concluded that MASWM is also a valid choice for subsoil exploration in Thailand. For the test configuration, it is recommended that the distance between the seismic source to the first geophone should be around 25 to 30% of the spread length. When using the same equipment and configuration, the investigation depth is limited to 20m. In addition, the sophisticated inversions are recommended for future research.