Reloading experimental research on the mechanical characteristics and failure mechanism of sandstone samples considering pre-peak cyclic loading
摘要
To mitigate surrounding rock stability issues induced by cyclic stress disturbance during tunnel excavation, pre-peak pre-damaged cyclic disturbance tests and true triaxial reloading tests on damaged sandstone were conducted using the GCTS triaxial rock test system (RTR-1000). An analysis was conducted on the mechanical behavior, energy conversion, and deformation mechanism of sandstone during the disturbance and true triaxial reloading processes under different intermediate principal stresses σ2 and disturbance frequencies f. A segmented softening damage constitutive model for the full stress-strain curve, which incorporates residual strength was established based on continuous damage mechanics and statistical damage mechanics. The research findings are as follows: (1) With the increase in σ1, the strain ε3 shifts from positive growth to negative growth as σ2 increases; the strains ε1, ε2, ε3, and εv all first decrease and then increase with the disturbance frequency f. (2) The failure angle θ of sandstone first increases and then decreases with the increase in σ2, and the higher the disturbance frequency f, the larger θ becomes. (3) Total strain energy and plastic strain energy show a trend of first decreasing and then increasing with the increase in f, while elastic strain energy gradually increases with f and dissipated energy exhibits the opposite trend. All energy parameters gradually increase with the increase in σ2. (4) The loading elastic modulus ELi is smaller than the unloading elastic modulus EUi; both elastic moduli exhibit a gradual increasing trend with disturbance frequency and also increase gradually with the increase in σ2. These findings provide a theoretical foundation for assessing the damage degree of rock masses and predicting the stability of surrounding rocks.