Constitutive Model and Microscopic Mechanism for Sandstone Strength Softening Damage

It is of great practical significance to study the microscopic mechanisms and strength damage laws of deep rock masses under the coupling action of water and rock. The pore structure and strength softening characteristics of sandstone under the action of different water absorption time are studied. Under the action of water-rock coupling, the cement between minerals dissolves and suspension loss of attached particles, which forms new pores and cracks, thus reducing the stability of the mineral structure. At the same time, the presence of hydrophilic minerals accelerates the speed of water absorption and softening of sandstone. It is found the relationships among sandstone stress, pore structure and water absorption time provide an evolution law for the microscopic pore structure during softening of sandstone strength, and a model diagram of the microscopic pore structure is established. Using the acoustic emission characteristics of water-rock coupling, the constitutive relationship between the accumulated ringing count of acoustic emission and stress under the action of different water contents is deduced. A comparison of experimental data with the model curve shows that the obtained constitutive model exhibits a high degree of agreement. Under the coupling action of water and rock, clay minerals are an important cause of rock strength softening, but there are certain limitations. Therefore, the softening mechanisms of some soft rock clays with little or no clay minerals should be further studied.