A Study on the Methods for Measuring In-situ Stresses at Great Depth by Use of Boring Cores

点击翻译按钮获取中文摘要

Anelastic strain recovery method (ASR method) and differential strain analysis method (DSA method) have been theoretically and experimentally investigated in order to enhance the reliability of the methods for measuring in-situ stresses at great depth. The main results obtained in this study were summarized as follows :1. ASR method(1) Anelastic strain recovery compliance (ASRC) ranges widely depending on the rock type. The ASRC in shear mode is greater than that in volumetric mode.(2) The ASRC of rocks depends on the mean stress. The mean stress increases the ASRC in shear mode and decreases that in volumetric mode.(3) A method for measuring three-dimensional in-situ stresses from anelastic strain recovery of a rock core has been proposed without assumptions except that the rock is isotropic and visco-elastic material.(4) The directions of principal in-situ stresses and the ratio of principal stress deviations in Yunomori district, Iwate Prefecture, have been successfully measured with the method developed in this study.2. DSA method(1) The physical Meaning of the crack parameters used in DSA method for measuring in-situ stresses have been clarified by theoretical consideration.(2) A testing system, whose main component is a pressure vessel of the capacity of 180 MPa, was constructed and the standard testing procedure for differential strain analysis has been established.(3) In-situ stresses have been evaluated by DSA method for the boring cores which were taken by over-coring technique for measuring in-situ stresses. The results from DSA method were not always consistent with those from over-coring methods.(4) The increase of crack parameters due to uniaxial tensile stress is not large enough compared to that measured by DSA for the rock speciments from in-situ. This suggests that the inconsistency described above is due to pre-existing cracks in the specimens.