Kozo Sugihara

APPLICATION OF TIME DOMAIN REFLECTOMETRY TO DETERMINATION OF VOLUMETRIC WATER CONTENT IN ROCK

Time domain reflectometry (TDR) is a widely used technique for measuring soil water content. To examine its applicability to rock, the authors applied TDR to a variety of rocks in the laboratory. The obtained relationships between the apparent dielectric constant and the volumetric water content showed a behavior that can be partly explained by the effect of gaps between the TDR probe and rock. For rocks with an effective porosity smaller than that of soil, the well-known model presented by Topp et al. [1980] for soil tended to overestimate the water content. For such rocks it was determined that an individual calibration was needed for accurate determination of water content. If no experimental calibration is possible, frequently used mixing models may be used to establish the calibration function. Our investigations suggest that TDR showed the potential for measuring the apparent dielectric constant of rock and, further, for determining water content in rock.

Preliminary results of a study on the responses of sedimentary rocks to shaft excavation

Abstract A shaft with a diameter of 6 m and a depth of 150 m was excavated in sedimentary rocks. Anin situ study was carried out to identify the size and rock properties of the zone disturbed by the excavation and to estimate the applicability of existing methods for measuring and modelling such a zone. The study detected displacements and changes in the properties of the rock within about 1 m of the shaft wall. Numerical analysis using a model of continuous rock mass can simulate some features of disturbance due to excavation, although slight discrepancies exist between the measured and analysed results. The excavation disturbance detected in this study is probably due to fracturing, the redistribution of stress and undersaturation. However, the relationships between the disturbance due to excavation and these processes have not been quantified. The existing methods for measurements and numerical analysis can provide important information on the disturbance due to excavation but need to be improved to understand disturbance due to excavation further.