Stress evolution of deep surrounding rock under characteristics of bi-modulus and strength drop

Aiming at the circular chamber under uniform stress field in deep energy storage and mining, analytical solutions of stress and plastic zone of the surrounding rock under different far-field stress and internal pressure were derived based on bi-modulus theory and the elastic-brittle-ideal plastic constitutive model. Evolution trend of the elastic-plastic stress and plastic region with different elastic constant ratios and residual strength coefficients were analyzed in details. Results revealed that when the internal pressure was small, the three-direction principal stress was compressive stress and the stress field distribution of the surrounding rock was not affected by the moduli difference. The obtained solution was consistent with the solution from the elastic-brittle plastic drop model under the equal modulus theory. On the other hand, when the internal pressure was large, the tangential stress was changed. The surrounding rock can be divided into three zones, i.e., tensile plastic zone (TPZ), tensile elastic zone (TEZ) and compressive elastic zone (CEZ). The tensile and compressive dual modulus had significant influence on the demarcation point between TEZ and CEZ. In addition, the strength drop and the dual modulus characteristic had a coupling effect on the stress distribution in the surrounding rock. The related achievements further enrich the theory of deep rock mechanics.