Abstract: 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.

Key words: overcore, borehole deformeter, three-dimensional stress