Abstract
To derive useful information of regional strain fields from the strain measurements in tunnels, we have investigated meteorological perturbations and reliability of instru ments. With regard to meteorological perturbations, remarkable strain changes of the order of 10-6 were caused by rainfalls and temperature changes in the 30 m shallow tunnel at Iwakura, Kyoto. However, these disturbances have not been observed in the Amagase tunnel, in which many instruments were installed at positions of 400-500 m from the entrance of the tunnel having a length of 1830 m, and the depth of the observa tion site from the surface is about 140 m. Reliability of instruments has then been examined for several types of extenso meter installed in the Amagase tunnel by comparing the observational results of tidal strains with theoretically predicted values. The result shows that tidal strains observed with the laser extensometer are closest to theoretical ones. Long term strain accumulations observed with laser extensometers in the Amagase tunnel are 3×10-7/year or so. We thus consider that the regional strain changes of the order of 10-7 can be detected without meteorological disturbances, if the reliable instruments such as laser extensometers are installed in a deep tunnel having a length of 5001000m.
