A seismic refraction survey for an expressway project in Singapore

Abstract

Geophysical methods of site investigation have been used in civil engineering for many years. Of these methods, seismic refraction survey is perhaps the most highly developed. This paper describes such a survey which was carried out for a proposed expressway in Singapore. The proposed 11 km expressway runs through the Bukit Timah Granite Formation. Acid rocks including granite, adamellite and granodiorite together with various hybrids, which were the results of the assimilation of basic rock within the granite, are present in the formation. Because of the local geological formations, the limited accessibility of the site, and the need for speed and economy, seismic refraction survey had been selected for the subsoil investigation. The study aimed to establish the depth of rockhead level, the type of subsoil materials and the foundation conditions for the planning and construction of the expressway and its flyovers and tunnels. Multi-channel equipment was used for the seismic survey. The energy source was explosives. This paper describes the field procedures and the techniques used for interpreting the results. The problems encountered and the limitations of this survey are discussed. In addition, the findings of the seismic survey are compared with the logs from the boreholes sunk into the bedrock along the expressway alignment. Generally, the results of the seismic survey were found to be satisfactory.