Authors: Dight, PM; Tarasov, BG; Hsieh, A; Dyskin, AV

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Dight, PM, Tarasov, BG, Hsieh, A & Dyskin, AV 2014, 'Estimation of in situ stress using the memory technique for deep mining', in M Hudyma & Y Potvin (eds), Proceedings of the Seventh International Conference on Deep and High Stress Mining, Australian Centre for Geomechanics, Perth, pp. 601-614.

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A series of tests are described in which the in situ stress has been recovered using the rock memory technique, known as deformation rate analysis (DRA), where the samples have been subjected to confinement (30 and 50 MPa). The rock samples comprised Urad Aplite Porphyry and were recovered from oriented core, drilled from a depth of approximately 1,550-1,650 m below surface lower than the current mine development. The oriented core is subsampled to obtain the test samples in six directions. The tests were performed in a sophisticated, very stiff triaxial stress cell. The unconfined compressive strength (UCS) of the rock was approximately 70 MPa. The maximum in situ stress was determined to be approximately 70 MPa. Based on experience the test procedure adopted typically loads the samples to a stress equal to three times the estimated overburden stress. In this case, that would be approximately 120 MPa, which would clearly exceed the UCS and hence the unconfined memory test would not have been applicable. Testing under confinement can increase the measurable stress difference, i.e. 1-3, and thus significantly extend the depth to which this technique can be undertaken when compared with unconfined tests suitable for other memory techniques. In particular, in the tests conducted, the confinement of 30 and 50 MPa raised the strength (1-3) from 70 MPa to between 170-270 MPa. Such an approach has implications for testing rock samples recovered from deep drilling where conventional testing could not reach the expected in situ stress without premature failure of the samples.

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