Underground engineering, especially deep geotechnical engineering, is often affected alternately by groundwater infiltration and ventilation drying during construction and use. In addition, acid rain, mineral dissolution, acid deposition, and other factors make groundwater acidic. This caused the underground structure to erode and has also threatened its safety and durability. In this study, both the physical and mechanical properties under acid dry‐wet (A‐D‐W) cycles were investigated. Deep sandstone was treated repeatedly under acid cycling, and its physical parameters were measured. Uniaxial compressive strength tests and microtests were carried out. Finally, using a combination of scanning electron microscopy (SEM) and backscatter electron images (BSE), the microstructural changes of sandstone under the combined action of an acidic environment and a dry‐wet cycle were described. The test results show that the mass, P‐wave velocity, peak stress, and elastic modulus of sandstone after the A‐D‐W cycles decreased by 0.43%, 7.87%, 70.20%, and 88.10%, respectively. With the increase in the number of cycles, the loss of these indicators increased. However, the peak strain increased with an average increase of 55.8%. In addition, 10 cycles are the critical point for physical and mechanical indicators of the A‐D‐W cycles. After 10 cycles, the changes of various indicators increase rapidly. Microscopic analysis shows that the reasons of this phenomenon were that the specimen was corroded by the sulfuric acid solution, which resulted in the development of pores and cracks and the decline of physical and mechanical properties. Conversely, the development of pores was hindered by sediment, which slowed down the decline rate of the physical and mechanical indexes of specimens, but this phenomenon disappeared with the increase of A‐D‐W cycles. Based on the analysis of the experimental phenomena, the constitutive model of uniaxial compression based on Weibull damage variable has been established in this article, and the model has the best effect in acid solution with less cycle times or pH value of solution greater than 6.

Water is one of the most important factors that affect the long‐term stability of geotechnical engineering structures. Rainfall often results in periodic changes in the water content in underground rock, which is subjected to alternating dry‐wet cycles. In this paper, in order to study the short‐term and long‐term mechanical properties of red sandstone under these dry‐wet cycles, a series of uniaxial compressive strength (UCS) tests and multistage creep tests have been carried out on specimens of red sandstone after being treated to different numbers of dry‐wet cycles. A scanning electron microscope (SEM) was used to image the different groups of specimens. The test results have shown that the peak strength and the elastic modulus of the red sandstone decreased as the number of dry‐wet cycles increased. It is worth noting that the first immersion of the specimens decreased their strength the most, and the negative logarithmic function was able to better reflect the peak strength of the red sandstone and the variation of its elastic modulus in relation to the number of dry‐wet cycles. The results of the creep tests have shown that the instantaneous strain and creep strain of the sandstone increased significantly with the increase of the number of dry‐wet cycles. A linear function and a negative logarithmic function can be used to describe the instantaneous strain and the creep strain, respectively. The creep duration of the red sandstone in its failure stage decreased with the increase of the number of dry‐wet cycles, and the creep rate increased with the increase of the number of dry‐wet cycles. Lastly, the failure modes of the red sandstone were observed; the results showed that the angle between the main crack and the axis of creep failure gradually increased with the increase of the number of dry‐wet cycles and the angle of the internal friction and the cohesion decreased. In addition, the failure mode of the specimens changed from tensile failure to shear failure. The microstructure of the sandstone showed that the surface of the specimen changed from being compact to being loose, and the mineral particles in the specimen changed from being spherical to being flat and curly; this led to a decrease in the macroscopic mechanical parameters of the sandstone.

In this study, a test technique that enables continuous control of the sample stress state from freezing to testing is proposed to investigate the influence of freezing pressure on the mechanical properties of ice under uniaxial compression. In this method, the water is frozen into the standard cylindrical ice specimen under high hydraulic pressure in a triaxial pressure chamber, and then, the temperature field and stress field of the ice specimens are adjusted to the initial state of the test; finally, an in situ mechanical test is conducted in the triaxial chamber. The uniaxial compression test of ice specimens with temperature of −20°C and freezing pressure of 0.5–30 MPa is performed in the strain rate range of 5 × 10⁻⁵−1.5 × 10⁻⁶ s⁻¹. The results show that, as the freezing pressure increases, the ductile‐to‐brittle transition zone of the ice specimen during failure moves to the low strain rate range, and the failure mode of the specimen changes from shear failure to splitting failure. Further, the brittleness index of the ice specimen first increases, then decreases, and then again increases with the increase in freezing pressure. The brittleness index reaches the maximum (minimum) when the freezing pressure is 30 MPa (20 MPa). The peak stress of the ice specimen also increases first, then decreases, and then increases with the increase in freezing pressure. The maximum value is also at the freezing pressure of 30 MPa, but the minimum value is obtained at the freezing pressure of 0.5 MPa. The failure strain of the ice specimen first decreases and then increases with the increase in freezing pressure, and the maximum (minimum) value is achieved at the freezing pressure of 0.5 MPa (10 MPa). When the ice specimen exhibits brittle failure, the relationships between the residual stress and the freezing pressure and between the peak stress and freezing pressure are the same, but when the ice specimen exhibits ductile failure, there is no obvious relationship between the residual stress and the freezing pressure.