To investigate the disturbance caused by blasting in the excavation process of tunnel and coal mine surrounding rock, it is urgent to clarify the mechanical response, failure mode and energy dissipation characteristics of red sandstone under dynamic load under confining pressure. In this study, the split Hopkinson pressure bar (SHPB) test system with a self-developed active confining pressure control device was used to carry out dynamic compression tests on red sandstone specimens under different confining pressure levels, to explore the dynamic mechanical response, failure mode and energy dissipation mechanism of red sandstone under impact load. The test results show that the stress-strain curve presents a “two stages” characteristics under unconfined condition. and the stress-strain curve changes from a “two stages” to a “three stages” pattern with the increase of confining pressure. The confining pressure significantly enhances the dynamic compressive strength and peak strain of red sandstone, both of which show significant strain rate effect and confining pressure effect. In terms of failure mode and energy dissipation, the rock specimen is crushed when subjected to higher strain rate at unconfined condition. Under confining pressure, the damage degree of the sample is significantly reduced, and finally resulting in compression-shear failure. Under the same confining pressure, the reflection energy and reflectivity increase with the increase of strain rate, while the transmission energy increases with the increase of strain rate and the transmittance decreases with the increase of strain rate. Under the same strain rate, with the increase of confining pressure, the rock reflection energy and reflectivity decrease, the transmission energy and transmittance increase. When the specimen is dynamically damaged, the dissipation energy is regulated by strain rate and confining pressure. When the confining pressure is constant, the dissipation energy and dissipation rate increase with the increase of strain rate. When the strain rate is constant, both the dissipation energy and dissipation rate decrease with the increase of confining pressure.

To explore the creep characteristics of carbonaceous schist under different moisture content conditions, based on the indoor graded loading creep test data, this paper constructed a viscoplastic body capable of describing the nonlinear accelerated creep stage throughout the entire creep process. This is achieved by parallelly connecting a nonlinear viscous element with a plastic element that characterizes yield behavior, based on data from indoor graded loading creep tests. Subsequently, this nonlinear viscoplastic body was integrated in series with the classical Nishihara model. By incorporating the softening patterns of elastic modulus and viscosity coefficient, four damage factors were introduced to establish a damage-based creep constitutive model (i. e., an improved Nishihara model) that describes the entire creep process of carbonaceous slate under different moisture content conditions. Through secondary development of a user-defined material subroutine (UMAT) in ABAQUS finite element software, numerical simulations of triaxial creep tests on carbonaceous slate under varying moisture content conditions were implemented. The applicability of the model was validated by comparing experimental creep data from rock samples with numerical simulation results. The research results show that the constructed improved Nishihara model can significantly improve the simulation accuracy in the accelerated creep stage. The graded loading creep test curves under different moisture content conditions are in good agreement with the numerical simulation curves, and the correlation coefficients are all greater than 0.9. The numerical simulation cloud map accurately reproduced the creep deformation evolution process of rock samples with different water contents, verifying the correctness and effectiveness of the proposed creep constitutive model of carbonaceous shale considering water damage and the development of the UMAT subroutine. This research achievement can provide theoretical support for the long-term stability assessment and disaster early warning of deep-water buried carbonaceous slate tunnel projects.