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.

In order to study the degradation laws and mechanisms of admixture concretes with single-added SO₄²⁻ and composite of Mg²⁺ and SO₄²⁻, respectively, the durability tests were conducted on three types of mineral admixture concretes (concretes with single-added metakaolin (MK), single-added ultra-fine fly ash (UFA), and composite of metakaolin and ultra-fine fly ash (MF), and one reference concrete. In these tests, the 10% Na₂SO₄ solution and the 10% MgSO₄ solution were used as the erosion medium, and the drying-wetting circle method was applied. It can be seen from the compressive tests and grey relational analysis that the MK admixture can improve the anti-Na₂SO₄-erosion capability of the concrete significantly, but weaken its anti-MgSO₄-erosion capability; the UFA admixture can improve both the anti-Na₂SO₄-erosion and the anti-MgSO₄-erosion capability of the concrete; and the composite admixture has superimposed effects and can enhance erosion resistance against these two erosion mediums. The phase composition and the changes of the macro morphology and the micro structure during the erosion process caused by mono sulfate ions and complex ions has been observed through X-ray diffraction (XRD), FTIR spectrum (FTIR), and scanning electron microscope (SEM), based on which it was determined that the erosion of single-added SO₄²⁻ ions can produce erosive outputs of ettringite, gypsum, and mirabilite in the concrete, and cause corner scaling or deformation. Mg²⁺ and SO₄²⁻ reacted in the concrete and produced brucite, M-S-H, ettringite, and gypsum, etc. The erosion of complex ions can cause scaling of the cement mortar and aggregate from the surface or the desquamation of corners.

Rubber concrete (RC) is a new type of concrete that is currently receiving a lot of attention, solving serious pollution problems by grinding waste tires into granules and adding them to concrete. However, rubber concrete has deficiencies in mechanics and durability, and has been reinforced by adding fibers in many studies. In this study, the mechanical and durability properties of rubber concrete with added polypropylene and basalt fibers (PBRC) were investigated in a series of experiments including apparent morphology, mass, static compressive and tensile tests, ultrasonic non-destructive testing, and scanning electron microscope (SEM) tests under coupled environments of sulfate attack and freeze–thaw. The results showed that the mass loss rate of RC and PBRC gradually increased with the number of freeze–thaw cycles, with more pits and cement paste peeling from the specimen surface. Moreover, the compressive and splitting tensile strengths of RC and PBRC groups exhibited distinct trends, with the former group showing a lower residual strength relative to the latter. The residual compressive strength of the RC group was only 69.4% after 160 freeze–thaw cycles in 5% MgSO₄ solution. However, it is worth noting that the addition of too many fibers also had a negative effect on the strength of the rubber concrete. Additionally, the scanning electron microscopy (SEM) results indicated that the fibers restricted the formation of microcracks in the microstructure and curtailed the brittleness of the concrete. This study can provide a valuable reference for the application of environmentally friendly material fibers in recycled aggregate concrete.

In order to enhance the corrosion resistance of concrete to chloride salt, 5% NaCl solution was used to corrode ordinary concrete (OC) and rubber concrete (RC) with 5%, 10%, and 15% rubber content, respectively. By testing the compressive strength, mass, chloride ion concentration at different depths and relative dynamic elastic modulus, the erosion mechanism was analyzed by means of SEM scanning and EDS patterns, and the mechanical properties and deterioration degree of ordinary concrete (OC) and rubber concrete (RC) under the corrosion environment of chloride salt were studied. The results show that: the quality of rubber mixed into concrete increases first and then decreases, and rubber can increase the compressive strength of concrete, improve its internal structure. At the same time, the mechanical properties of concrete in the corrosion environment of chloride salt are improved to a certain extent, and the deterioration degree is reduced. Considering the comprehensive performance of OC and RC in the dry–wet alternation mechanism under chloride salt corrosion, the best content of rubber is 10%.

Due to various factors, high-temperature rocks are often affected by different cooling methods. They will lead to changes in rock mechanical properties, which firmly connect with the safety and stability of practical projects. At present, there are many studies of the microscopic characteristics of rocks under different cooling methods, but few on the mechanical characteristics of rocks under the same conditions. Therefore, it is necessary to carry out experimental research on the mechanical properties of rock under different cooling methods. The study shows that the deterioration degree of the sample increases gradually with temperature rising and the cooling methods have different effects on the change of the sample in mass, volume and density. The stress–strain curve of the sample is divided into the crack compaction stage, elastic deformation stage, nonlinear deformation stage and failure stage. The peak strength of the naturally cooled sample is higher than that of the water cooled. The peak strength comes with a trend that goes up first, and then down with the temperature increasing. The uniaxial compression failure of the sample under uniaxial action is tensile failure. The failure characteristic of the sample is influenced both by the cooling modes and the temperature.