doi:10.3850/978-981-08-6396-8_P119

ABSTRACT

This report introduces one of the geophysical methods, Geotomography, which was performed to investigate and analyze the mixed ground condition of the Downtown Line Stage-2 Contract 915 (DTL2 C915) in Singapore. The main scope of DTL2 C915 is to construct 2.3km twin tunnels utilizing Slurry Shield TBM’s between stations at Beauty World and Hillview along Upper Bukit Timah Road which is west of Bukit Timah Hill. Bukit Timah Granite, Hypogene rock, is widely developed throughout the section, and Dike rocks intruded to the bed rocks partially appear. According to the result of geological pre-investigation, there are nine (9) mixed ground zones appearing throughout the tunnel alignment. The distinctive property of these mixed ground zones are that the residual soil and protruded shape of high strength granite with unconfined strength ranges from 50MPa to 200MPa create a distinct contrast. To verify the scale and shape of the mixed ground, Geotomography, the cross hole seismic survey method was applied. In order to generate seismic energy for investigation, detonators were used as a source based on considerable experience in Korea. In order to verify the accuracy of this method, the applicability test was performed and the result of test was directly compared with the rock boundary recognized from SI boreholes which were drilled to check the accuracy of the Geotomography. The 9 mixed ground zones and 2 special zones have been presented for the Geotomography survey, and those will be utilized as a baseline for the ground improvement plan.

Keywords: Geotomography, Rock head profile, Bukit timah granite, Slurry shield TBM.

© 2010 WUTC Organisers