A NEW 3D IN-SITU ROCK STRESS MEASURING METHOD:BOREHOLE WALL STRESS RELIEF METHOD(BWSRM) AND DEVELOPMENT OF GEOSTRESS MEASURING INSTRUMENT BASED ON BWSRM AND ITS PRIMARY APPLICATIONS TO ENGINEERING

Abstract

It is important to conduct a research on the stress state of the rock masses in the upper earth′s crust.In-situ rock stress measurement is the basic and reliable access to obtain the stress state of the rock masses.The development of in-situ rock stress measurement and state-of-art of research on it are overviewed.Then,several in-situ rock stress measuring methods and techniques are briefly analyzed in rock mechanics and engineering.A new method,borehole wall stress relief method(BWSRM) to determine the in-situ 3D rock stress tensor in a single drilled borehole is deliberated.An original geostress measuring instrument typed by BWSRM-H01 is designed and manufactured based on the principle of in-situ rock stress measurement with BWSRM.The in-situ test for rock stress with BWSRM is carried out at an experimental tunnel in Jinping II hydropower station,China,where the buried depth of overburden is about 2 430 m.It is shown that the two principal stress components close to the horizontal direction are the maximum and intermediate principal stress respectively;while the stress component close to vertical direction is just the minor principal stress in the testing site.The magnitudes of the maximum and the intermediate principal stress are high;and both of them are very close.