Experimental study on rock mechanical behavior retaining the in situ geological conditions at different depths

Understanding the real physical and mechanical characteristics of deep rocks under in situ geological conditions is fundamental for deep rock engineering. Rock mechanics that retains the in situ geological conditions is defined to study the rock behaviors under the in situ geological conditions (geostress, temperature, pore pressure, etc.). A new experimental methodology called the in situ stress restoration test is proposed to recover the in situ geostress conditions of a core as closely as possible. Cores obtained from 10 different burial depths are used to carry out in situ stress restoration tests and triaxial compression tests. The results of the two kinds of tests indicate that in situ stress restoration would heal the damage induced by removing the in situ geostress during the coring process to a certain extent. Compared with the rock mechanical behaviors observed during the triaxial compression tests, the peak strength, residual strength and elastic modulus are higher during the in situ stress restoration tests. In situ stress restoration can make a core less brittle and enhance its inelastic deformation, including strain hardening and strain softening, especially at deeper burial depths. The elastic energy density, dissipated energy density and total energy density are all higher during the in situ stress restoration tests than those during the triaxial compression tests for the different rock types and burial depths. The proposed experimental method can consider the effects of the in situ geostress to only a certain extent. Rock experimental techniques that can comprehensively reflect all the in situ geological conditions at different depths should be further studied.

Automated summary

The in situ stress restoration test can partially repair the damage caused by the removal of in situ geostress during coring, making the rock more elastic and enhancing its inelastic deformation characteristics. This experimental method helps to understand the real physical and mechanical properties of deep rocks.