Fracture mechanism and constitutive model considering post-peak plastic deformation of marble under thermal-mechanical action

Abstract

Temperature plays an important impact on rock mechanical properties. In this paper, the mechanical properties, fracture mechanism and constitutive model of marble under thermal-mechanical action are studied by experimental and theoretical methods. The results show that the deformation of marble under the condition of 20-120 ℃ and 15 MPa can be divided into four progressive failure stages: compaction, linear elasticity, crack propagation and post-peak failure. The stress-strain curve is not obviously affected by temperature, characterized by strain softening and plastic deformation. The macroscopic fracture characteristics change from shear failure to tensile mixed failure with the increase of temperature. With the increase of temperature, the strength of marble tends to decrease, indicating that temperature increase has a weakening effect on marble, and there are temperature-sensitive areas of 20-60℃ and temperature sub-sensitive areas of 60-120℃. The elastic modulus of marble decreases and Poisson's ratio increases with increasing temperature. The energy evolution law of marble under different temperature is basically the same, which shows that before crack initiation, the energy dissipation is less, and after the damage and yielding occurs, the energy dissipation increases quickly. The energy dissipation in the failure process is mainly used for crack initiation-connection-penetration, as well as plastic deformation caused by friction and slip of cracks, and the plastic deformation and energy dissipation have good linear characteristics. The statistical damage constitutive model based on three-parameter Weibull distribution function can effectively reflect the characteristics of post-peak plastic deformation and strain softening. The weakening effect of marble at 20-120℃ is related to its internal moisture excitation. With the increase of temperature, water is stimulated to absorb and attach to the original relatively dry interface, which plays a role in lubrication. The relative motion friction resistance between solid particles or crack surfaces decreases, which leads to crack initiation and friction energy consumption reduction, changes the specific surface energy of rocks and weakens the strength of marble. The results provide a theoretical basis for predicting and evaluating the long-term stability and safety of surrounding rock of underground deep engineering in complex environment with high ground temperature and high geo-stress.