A Study on the Methodology of Estimating the Rock Classification with the Seismic Exploration in Mountain Tunnel Construction Projects
Hiroyasu OHTSU, Kazuo SAKAI@and Nobusuke HASEGAWA
Abstract:In mountain tunnel construction projects, geological surveys as typified by borehole exploration and seismic exploration are conducted prior to design works by project owners. In this investigation phase, the limitation of budget allocated to survey makes it impossible to construct a lot of boreholes, which figure out the correct geological condition but lead to substantial cost. Seismic exploration result therefore has a large share of estimation of geological condition. However, in the estimation with seismic exploration, there are some accuracy problems caused by assumptions for seismic velocity analysis. In fact, some cases that ground condition in construction phase differs substantially from that in design phase. From such a view point, this study aims at developing a reasonable methodology estimating the ground condition by integration of seismic exploration result and borehole exploration result. In details, seismic velocity in the project site is estimated by them with eexternal drift kriging methodf, which is one of the geostatistics methodologies. And, ground condition is estimated by the seismic velocity with the core point evaluation method calculated by tunnel face point evaluation. Furthermore, this methodology has been applied in the actual mountain tunnel construction project. Finally, the result made it clear that methodology proposed in this paper was very effective to estimate the rock classification for a mountain tunnel design. Key Words:Rock classifications, Mountain tunnel, Geostatistics, Seismic exploration