The seismic refraction survey from the ground surface has been routinely applied to planning of tunneling as a preliminary survey. A tunnel support pattern is designed based on seismic wave velocity of the ground obtained by seismic refraction survey. Where overburden on a tunnel is large, the resolution in velocity structure by this technique becomes poor. The authors developed a new exploration method by the use of drilling vibration data called T-SPD (Tunnel Seismic Probe Drilling) to estimate seismic wave velocity distribution ahead of the tunnel face to be utilized for designing tunnel support patterns. The field tests of T-SPD have been carried out at three tunneling sites. In this paper, the authors will report two field tests using the drill machines, one with 100m and the other 1,000m capacities. P-wave velocity distribution estimated by T-SPD was found to agree with P-wave velocity distribution estimated by seismic refraction survey from the ground surface and on the roadbed in the tunnel. Two field tests confirmed T-SPD can be an alternate exploration method of seismic refraction in case seismic refraction from the ground surface is difficult to be applied due to large overburden.

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