| 摘要 |
<p>PROBLEM TO BE SOLVED: To measure the propagation speed of underground electromagnetic waves with high accuracy. SOLUTION: A single transmitting antenna 16a and, for example, three receiving antennas 16b1-16b3 are provided in the vicinity of the tip part of a driller in an underground jacking method. Based on the reflection time of reflected waves by each of the receiving antennas 16b1-16b3 and the known distances between the transmitting and receiving antennas, a propagation speed (v0) is computed and obtained. In addition, the intensities of the reflected waves is added up along a hyperbola corresponding to a previously set propagation speed (vi) in the two-dimensional plane of the distance between the transmitting and receiving antennas and elapsed time, and the propagation speed (vi) at which a maximum added-up intensity is obtained is determined as an actual propagation speed (v0).</p> |
