The influence of acid solution and immersion time on the physicomechanical properties of sandstone is investigated. Uniaxial compression tests on sandstone samples are conducted to determine the variations of relative mass, deformation, and strength characteristics of sandstone subjected to different pH sulfuric acid corrosion values. The changes of pH and Mg²⁺ and Ca²⁺ concentration of immersion solutions are monitored during soaking. The corrosion mechanism of sandstone attacked by the acid solution is discussed with the results of SEM tests. Based on the nondestructive CT scanning test, the damage variables of acid‐corroded sandstone are deduced, and the damage degree of sandstone is quantitatively analyzed. The results indicate that the deformation characteristics of sandstone samples under acid attack are characterized by the softening of rock, and the softening degree gradually increases with the increase of the acidity and the soaking time. The peak strength of sandstone samples declines as soaking time extends. The chemical effects lead to a large amount of dissolution of the rock mineral assemblage, resulting in the large‐scale development of the pores inside the rock, which changes the macroscopic mechanical properties. The damage variables of acid corrosion sandstone based on CT numbers are deduced, and the quantitative relationship between damage variables and immersion time is established, which provides a basis for constructing a damage constitutive model of sandstone in the acidic environment.

The 28 days cured cement mortar samples were soaked in HCl (pH = 1 and 2) and H₂O (pH = 7) solutions for 90 days. By monitoring the ion concentration of H⁺ and Ca²⁺ and measuring the changes in weight loss, longitudinal wave velocity, and uniaxial compressive strength values of the corroded mortar, the physicochemical and mechanical properties of the mortar specimens were studied. Experimental results indicate that the process of the mortar sample subjected to HCL erosion has apparent stage characteristics. In the initial stage of corrosion, the chemical reaction increased the porosity of the specimen, which leads to the decrease of longitudinal wave velocity of the samples. At the same time, the corrosion solution continuously penetrates into the mortar pore system, which leads to the increase of the mass, and it is considered that the diffusion process plays a leading role during this period. Moreover, the colloidal compounds generated by the chemical reaction can not only fill the pore space but also block the continuous reaction, which led to the increase of the longitudinal wave velocity of the specimen. With the prolonging of corrosion time and infiltration path, the pH value and the concentration of Ca²⁺ tend to be stable, the diffusion action is weakened, and the chemical reaction is continuous, which led to the decrease of the mass and wave velocity gradually. It is considered that the chemical reaction plays a leading role in this process. Based on the induction and analysis of the test results, a generalized porosity model regarding the increase of the porosity and the decrease of effective bearing area of the mortar sample was proposed. The relation between the uniaxial compressive strength and the corrosion time of the corroded mortar is deduced, and the unknown parameters are determined based on the regression analysis of the test data.

During the excavation process of a large-span variable cross-section of a tunnel, the deformation and stress characteristics of the surrounding rock supporting the structure are complex, and construction control is difficult. Based on an actual tunnel project, the mechanical effect and deformation characteristics of the surrounding rock and support structure of a large-span variable cross-section tunnel during its excavation and support process were studied via numerical simulation. The construction method, using the bench method to excavate and set up the transition section in the variable cross-section, was proposed. Based on the numerical simulation results, two optimized excavation schemes were proposed and analyzed to address the construction method conversion problems in constructing large-span variable cross-section tunnels. The rationality of the optimized construction scheme was verified through a comparison with field monitoring data. The research results show that the three-bench temporary inverted arch method supported by the temporary vertical portal frame has good applicability in constructing the large-span variable cross-section tunnel. This scheme can effectively control the stress concentration and excessive deformation of the surrounding rock in the large-span variable cross-section tunnel. The numerical simulation results agree with the field monitoring data, which verifies the rationality of analyzing the construction mechanical effects of variable cross-section tunnels and selecting construction schemes through numerical simulation. The research results can provide reference for the construction of similar tunnel projects.

The physicomechanical deterioration characteristics of sandstone subjected to H₂SO₄, HCl, and H₂O solutions of different pH values are studied by the method of long‐term accelerated immersion. The quantitative relationships between the damage variables based on CT (computer tomographic identification technology) numbers and the immersion time, the uniaxial compressive strength, the peak point strain, and the elastic modulus of rock samples are analyzed. The test results indicate that the pH value of immersion solutions, the dissolution rate of Ca²⁺ and Na⁺, and the quality change of rock samples show visible stage characteristics under acidic environment. With the soaking time extended, the pH value of solutions increases gradually, and the quality change of rock samples decreases gradually. The smaller the pH value of immersion solutions is, the higher the dissolution rate of Ca²⁺ and Na⁺ is. However, the cation dissolution rate under a weak acid environment with a high pH value has little difference with that under the distilled water (pH = 7). With the increase of the soaking time and the acidity, the compaction stage of rock samples becomes longer, the elastic stage becomes shorter, the deterioration degree of mechanical parameters becomes more extensive, and the destruction of sandstone samples shows ductility characteristics increasingly. The corrosion degree of corroded sandstone samples is quantitatively represented by microscopic damage variables based on CT numbers. The regression analysis results show that damage variables of acid‐corroded sandstone samples have a power function relationship with soaking time and an exponential function relationship with peak strength, peak point strain, and elastic modulus.