Experiment on mechanical properties of conglomerate rocks under true triaxial loading

Key words:  conglomerates  true triaxial experiment  strength characteristics  CT scanning  failure mechanism

Abstract:

Kuqa region in Tarim Basin China has a great potential for oil and development. However, it has multiple thick layers of conglomerate rocks with high strength and hardness, posing a great challenge to well drilling. In this study, in order to analyze the strength and failure mechanisms of the conglomerate rocks under different loading states, a true triaxial experiment was carried out using outcrop rock samples of the conglomeratein the region. A CT technique was used to scan the rock specimens in the triaxial experiments to reveal the failure process of the rock. The experimental results show that the failure process and strength characteristics of conglomerate rock under true triaxial loadings are significantly affected by horizontal principal stress with the rock being subjected mainly to brittle failure. The strength of the rock increases linearly with horizontal principal stress, while its elastic modulus, lower than the uniaxial elastic modulus, is less affected by the horizontal principal stress. Because of the heterogeneity and various conglomerate components (i.e. gravels) with different strength, the deformation of the matrix rock can lead to different loadings of forces on the gravel particles, which can induce shear failure and cracks around the gravels, eventually leading to the macro failure of the conglomerate rock.