ABSTRACT
Alignment of twin bored tunnels in Contract T217 of Thomson East Coast Line (TEL) runs through challenging ground of Bukit Timah Granite formation consisting of mixed faces and full face granite. One of the challenges in tunneling was to under cross several residential buildings in mixed face conditions. Parallel seismic method and borehole radar survey was employed for investigation of foundations of some of the buildings to cross verify foundation details with as built foundation drawings. Careful control over parameters of Tunnel Boring Machine (TBM) was exercised to mitigate risk of over excavation. In cases of over excavation where access from surface for grouting of void was not available, especially when tunneling underneath buildings, the procedure for grouting from the TBM was developed. This paper describes challenges during tunneling in mixed face conditions underneath several houses.
