In consideration of the influence of energy dissipation on the rock compression process, the traditional elastic stress-strain relationship was improved by adding the energy release rate. The microintensity of the rock was assumed to satisfy the Weibull distribution. The improved stress-strain relationship was transformed into a triaxial stress-strain model in consideration of the loading damage combined with mesodamage mechanics. The characteristic points of the stress-strain curve and the experimental data were utilized to calculate the distribution parameters of the rock under different conditions. The model curve was compared with the experimental data. Results showed that the stress-strain curve of the rock has peak points in the conventional triaxial compression test, but the radial peak of the rock was not evident in the unloading test. The energy of the rock under the loading path was smaller than that under the unloading path. The model curve exhibited a high degree of fitting with the experimental data, and its correlation coefficient was relatively large (> 0.90), which indicated that the model can clearly represent the actual damage and evolution law of the surrounding rock. Furthermore, the established model can also reflect the rock’s stress-strain relationship, which can serve as a practical guide for relevant applications. Finally, the distribution parameters also reflected the evolution law of rock energy and provided a method for the assessment of rock energy and damage trend.

In order to study the creep characteristics and mechanism of red-bed soft rock under the water–rock interaction, fluid–structure coupling triaxial compression tests and creep tests under stepwise loading were carried out. Furthermore, the influences of seepage pressure and stress on creep deformation, long-term strength, Poisson’s ratio, and seepage velocity were analyzed. According to the experimental results, the influence of seepage on the creep of soft rock cannot be ignored. The results show that the seepage leads to a decrease in triaxial strength and long-term strength, and an increase in instantaneous deformation and creep deformation. The failure mode of triaxial compression changes from shear failure to tension-shear conjugate failure, whereas the long-term strength of fluid–structure coupling creep is 60%~70% of the triaxial strength. When the stress level and seepage pressure are relatively small, the Poisson’s ratio of creep increases with the increase of seepage pressure, and the radial creep deformation response lags behind the axial creep deformation. However, at a high stress level and osmotic pressure, the Poisson’s ratio and seepage velocity increase rapidly, and the duration of the accelerated creep is obviously shortened. Through the analysis of the influence of seepage pressure on the seepage velocity, with the increase in the seepage velocity, the seepage velocity changes and fluctuations are more obvious, which further confirms the damaging effect of seepage pressure and erosion on the internal structure. In the field monitoring of actual engineering, the rapid change of seepage velocity can be used as a precursor signal to predict the instability. Therefore, the water–rock interaction cannot be ignored in the analysis of mechanical properties and long-term stability of red-bed soft rocks.

Groundwater in southern China region contains various chemical compositions. By comparing the effects of acidic, neutral, and alkaline solutions on mechanical properties and internal structure, the changes in mechanical parameters and microstructure of chemical solution etched samples were obtained. The results show that as the pH of the solution increases from 2 to 12, the peak strength and elastic modulus of the rock samples initially increase and then decrease, while axial strain and Poisson’s ratio first decrease and then increase. The degree of deterioration of rock samples by different chemical solutions follows the order strong acid (pH ≤ 4) > strong alkali (pH ≥ 10) > weak acid (4 < pH ≤ 6) > weak alkali (8 ≤ pH < 10) > neutral (pH = 7). Alkaline and neutral solutions mainly corrode the surface of rock samples, with the wave velocity of the rock core higher than that of the surface. The wave velocities of alkaline solutions at different pH values after corrosion are essentially the same as that of pH = 7 neutral solution, ~2,850 m/s. Acidic solutions corrode both the surface and core of rock samples, with the wave velocities of the core and surface being similar. After corrosion by pH = 2 acidic solution, the wave velocity of the rock samples decreases to 2,505 m/s. With increasing acidity or alkalinity of the chemical solution, the internal pores of the rock transition from micropores to mesopores and macropores. Compared to pH = 7 neutral solution, the porosity of rock samples increases by 59.13% and 24.17% after corrosion by pH = 2 and pH = 12 solutions, respectively. Acidic and alkaline solutions exhibit distinct mechanisms: acidic solutions corrode particles and framework to form continuous fractures, whereas alkaline solutions generate new substances filling the fractures through hydration reactions. By introducing chemical damage variables and considering threshold factors, a chemical damage constitutive model is constructed to effectively describe the impact of chemical corrosion on mechanical properties. This systematic study of the chemical environment’s influence on internal structures reveals the erosion mechanisms of acidic, alkaline, and neutral saline solutions, which is crucial for the stability of underground engineering surrounding rocks and geological disaster prevention in southern China.

The red-bed soft rocks in South China have obvious creep characteristics and are prone to engineering geological disasters such as landslide and foundation settlement under the action of rainfall, groundwater, and load. In order to reveal its creep characteristics and mechanism under complex conditions, a step-loading creep test was carried out under chemical-stress-seepage coupling, and the energy evolution law of the whole creep process was analyzed based on linear energy storage and energy dissipation theory. The results also show that the acid chemical solution has the greatest influence on the triaxial strength and creep strength, and the creep damage and energy evolution of red-bed soft rock are universal. The creep damage and total strain increase with the increase of acidity, the decrease of confining pressure, and the increase of seepage pressure. The evolution law of creep damage shows the characteristics of slow-acceleration-rapid growth, and with the increase of load level, it has obvious transfer and accumulation. After entering the constant velocity creep stage, the damage rate begins to accelerate. The proportion of instantaneous strain and creep strain in the total strain increment is about 50%, and confining pressure has little influence on their respective proportions. The instantaneous strain is more sensitive to the acidity of the chemical solution, and the proportion of creep strain increases gradually with the increase of seepage pressure. The relationship between elastic energy density and total energy density is linear. The elastic energy density and dissipated energy density in the loading stage and creep stage all increase nonlinearly with loading time. The density of dissipated energy in the creep phase is lower than that in the loading phase, but the opposite is true in the higher stress phase, and the law of energy dissipation can explain the hardening damage effect in the creep process of soft rock samples. The research results provide a new perspective for us to reveal the mechanical properties and failure mechanism of red-bed soft rocks and provide an important theoretical basis for predicting and evaluating the creep instability and long-term stability of such rocks.

In underground engineering, reinforcement is a necessary means to ensure the stability of surrounding rock. Due to the stress redistribution caused by excavation disturbances, the reinforced rock mass is frequently subjected to loading and unloading, and its mechanical properties change accordingly. Based on the above engineering practice, using pasted circular CFRP, an approximate simulation of the rock reinforcement effect of bolt and shotcrete support was performed. Triaxial cyclic loading and unloading tests of reinforced sandstone were carried out, and the influence of different reinforcement schemes on the mechanical properties was compared and analyzed. Furthermore, the strengthening mechanism, damage evolution, and energy transformation mechanism of CFRP are discussed. The results showed that the peak strength increased about 14.2% and 23.8% with the two reinforced schemes, and the residual strength increased about 27.3% and 52.8% with the increase in the area reinforced by CFRP. Under the same confining pressure and strain conditions, the characteristic energy density and elastic energy ratio increased with an increase in the reinforcement area, but the damage variable decreased. It is proved that CFRP can improve energy absorption efficiency, enhance the energy storage limit, and reduce dissipation efficiency. By inhibiting the propagation of internal fissures and limiting the energy dissipation during fractures, the rock mass can be restrained and strengthened.