回転探触子型岩盤割れ目検知計による現場試験

岩盤内の割れ目の分布と音速の変化に関する研究 (続報)

抄録

It has become very important in estimating the strength, the permeability and the other properties of rock to detect the distribution, the direction and the width of cracks in rock.
A crack-detector which can obtain the crack distribution and the sonic velocity change in rock, as already stated in 1st report, had been developed in this study.
The in-situ tests using a crack-detector which improved the inadequate points of the old type crack-detector are described in this report. It is the characteristic of the new type crack-detector with rotating two probes as show in Fig. 1 that the time required for a round measurement of its crack-detector is saved than that of the old type crack-detector.
The results obtained from the basic and the applied research for the study of crack distribution and sonic velocity change in, rock are as follows.
1) As basic research for this study, the measurements of crack distribution and sonic velocity change were made on the surface of concrete floor with cracks. The results obtained from the basic research are shown in Fig. 3. The maximum value of sonic velocity of concrete floor, as shown in Fig. 3, is nearly equal to that of the concrete specimen. It is also clear that the patterns of pulse waves differ in the condition of concrete floor, that is the intact parts, the parts with closed cracks and the parts with open cracks, as shown in Fig. 2.
2) At Yaguki mine, Fukushima prefecture, the crack distribution and the sonic velocity change of rock were measured by inserting the crack-detector in NX boreholes. From the measurements, it is seen that the maximum value of sonic velocity in Fig. 6 is nearly equal to the velocity of specimen which is collected from the rock. Considering that the amount of scatter of sonic velocity as shown in Fig. 6 is closely related to the properties of rock, the correlation between the coefficient of variation of sonic velocity and RQD (Rock Quality Designation) obtained from NX- boring core is investigated. It is recognized from Fig. 7 that the coefficient of variation has linear correlation with RQD.
3) The results of in-situ measurements at the underground of Shakanai mine, Akita prefecture, are similar to those at Yaguki mine, as shown in Fig. 10. But, the coefficient of variation of sonic velocity has not a correlation with RQD, because the rock situated in where in-situ measurements are performed has many fractures along the core axis.