Determining 3D in-situ stress with a new borehole deformeter by single overcore

Based on the overcore method used in measuring initial geostress of rockmass and the borehole deformeter 36-2,a new twelve components borehole deformeter is devised.Compared with the former 36-2 borehole deformeter,which has only four radial deforming measurement elements,the new type has eight more axial elements.Its sensitivity and accuracy is each 0.0001mm and 2‰.A great number of calibration tests in laboratory manifest its sensitivity for stress measurement will reach 0.028MPa(while E=30Gpa).The deviation between true stress and measured stress is not greater than 10%.Using the twelve components late-model borehole deformation gauge,you will obtain three-dimensional stress(or total stress) state of one point only by once overcore test.This test equipment successfully overcomes the disadvantage of measuring three-dimensional geostress with the traditional thrice overcore test;and it enables remarkable economic benefit,convenient operation and higher reliability.