Measuring vs30 using surface wave tests

• Main Author: Chau, Glenn Wen Hon
• Other Authors: Leong Eng Choon
• Format: Final Year Project
• Language: English
• Published: 2014
• Subjects: DRNTU::Engineering
• Online Access: http://hdl.handle.net/10356/61202
• Institution: Nanyang Technological University

Given that Singapore has adopted the Eurocode since 1st April 2013, there is a need to test out methods to obtain the average shear wave velocity or VS as it is one of the main parameters used in the classification of ground types. The usual parameter involving VS is the VS,30 or the average shear wave velocity of the top 30m of soil layer. This project focuses on a specific type of site test, the continuous surface wave system (CSWS) test. This is a non-invasive test method that involves a vertically oscillating mass vibrator, geophone receivers, a CPU and a vibrator control unit. Seismic waves are sent into the ground by the vibrator and the geophone receivers pick up the corresponding phase angles. The receivers are placed at different offset distances during the course of each site test to ensure homogeneity in the ground layers. The objective of the field tests is to acquire parameters that will aid in the calculation of the shear wave velocity profile, which will lead to the VS,30 value being able to be obtained. The results from six test sites in Singapore were taken and analyzed. In order to produce the shear wave velocity profile, inversion process had to be used and for this project, the weighted average velocity (WAVe) method was employed. Also, it has to be noted that for all the test sites, the depth of penetration of the seismic waves into the ground did not reach 30m. As such, the VS,30 value could not be obtained directly but instead, a correlation method had to be used to estimate the VS,30 value. It was shown that although both the VS,5 and VS,10 values could be used to estimate the VS,30, they were not very accurate as three out of the six values were out of the historical data range of their respective sites. It was seen that while the CSWS tests were not a very accurate measure to estimate the VS,30 values, it was still useful as a rough guide to obtain the ground classification type.