Cross-hole Seismic Travel Time Tomography Applied before Tunnel Excavation by using TBM

A tunnel with a dual function was built in the city of Kuala Lumpur - Malaysia in order to solve flood and traffic congestion problems. Before tunnel was built by using Tunnel Bore Machine (TBM), several surface geophysical surveys were conducted in order to predict subsurface condition, especially the possibility of cavities inside limestone/marble of Kuala Lumpur Limestone formation to be occurred. Cross-hole seismic travel time tomography was conducted before the TBM excavated the subsurface below Istana Island area in Kuala Lumpur, Malaysia. This area is known as very difficult area, in which it is situated on a highway that is connected Kuala Lumpur and other cities in southern part. There is no possibility to conduct geophysical surveys, except cross-hole seismic tomography. The reprocessing of tomographic data is aimed in order to obtain better velocity model. The obtained result quality is improved, since the used inversion scheme is more stable in handling the data. Checker-board resolution test is also conducted in order to determine the tomogram areas that are reliable to be interpreted. As conclusion, it is hoped that this method could be accepted in the tunnel business if the TBM path must excavate though complicated surface situation.