Abstract
Knowing the geological condition ahead of a tunnel face can reduce to unexpected events, and it can also contribute to cost-reduction and to achieve more rapid construction. Exploration technique described here is an application of the so-called reflection method. The estimation of a geological changing point was carried from the measurement of strikingvibration by a hydraulic rock-breaker when performing excavation work. The receivers are fixed on the head of rock bolts via installation tools, so it is never almost inhibit usual construction cycles. The reflecting position was estimated from the finding a common point on travel-time ellipses. By repeating this work while the excavation work, the exploration accuracy can be expected to improve. As a result of the field experiment in some tunnels, effectiveness of this method was confirmed.
