In this study, Tunnel Seismic Prediction method (TSP) was used to predict the geological condition ahead of the tunnel face. The tunnel which extends 44.6 km is intersected by several major faults and few lineaments. The ability of the TSP system was investigated to predict one the anticipated fault which had been inferred from the geological map. Then, the TSP results were applied to delineate the relation between seismic velocities and geological parameters for the predicted fault ahead of the tunnel face. The results show a velocities drop 10 to 40m ahead of the tunnel face which had indicated the initial findings of the unfavorable geological condition from geological map. From the verification analyses, the TSP results are substantially correlated with the Tunnel Boring Machine (TBM) driving data, geological mapping, rock class grade point and uniaxial compressive strength obtained using Rock Schmidt Hammer. In this case, the TSP was a helpful tool for the tunnel contractor in predicting zones of geological instabilities during the excavation process of long deep tunnel. Thus, such prediction method can be used as a decision support in the observational design and construction system especially in determining suitable tunnel support system in the expected unfavourable geological conditions.

1 Introduction

The tunnel boring machine has been used all over the world because of its advantages such as higher excavation advance rate compare to drill and blast, smooth tunnel face which lead to less excavation disturbed zone and suitable to be used for long tunneling, thus reducing the number of adit of shaft that need to be constructed. However, if there is some unfavorable geological conditions such as collapse, overbreak, or weak zone due to the existence of faults and fractured zones, the progress of the excavation is disrupt, making it impossible to fully achieve the high advance rate capability of the TBM. It is important, especially in the construction of long tunnel like Gotthard Base Tunnel and Seikan Tunnel that have hugh challenge due to its complex and changing geological conditions to have a reliable and detailed information of the ground conditions especially ahead of the tunnel face to foresee any ground diificulties that might be encountered and to prepare appropriate countermeasures to lease the effects.

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