Study on Mechanical Behavior and Energy Mechanism of Sandstone under Chemical Corrosion

Chemical corrosion has a significant impact on the properties of rock materials. To study the mechanical behavior and energy mechanism of rock under chemical corrosion, this paper took the sandstone of Haitangshan tunnel in Fuxin as the research object, used a Na₂SO₄ solution to simulate different chemical environments, carried out a triaxial loading test on sandstone through the MTS815.02 test system, and analyzed the mechanical parameters and energy damage evolution law of sandstone under different chemical environments. The test results showed that the basic mechanical parameters (peak strength σ_pk, peak strain ε_pk, elastic modulus E, cohesion c, and internal friction angle φ) and characteristic stress parameters (closure stress σ_cc, initiation stress σ_ci, and dilatancy stress σ_cd) of sandstone first increased and then decreased with the increase of pH in the Na₂SO₄ solution, Poisson's ratio µ showed the opposite trend, and the extreme values of all parameters were taken when pH = 7. The influence degree of different pHs on the mechanical parameters of sandstone were as follows: strong acid environment (pH ≤ 4) > strong alkali environment (pH ≥ 10) > weak acid environment (4 ≤ pH < 6) > weak alkali environment (8 ≤ pH < 10) > neutral environment (6 < pH< 8). The total energy and elastic strain energy increased first and then decreased, and the dissipated energy was the opposite. The damage variable decreased first and then increased. With the increasing concentration of the Na₂SO₄ solution, all the above parameters changed monotonically. Based on the energy theory, the damage evolution equation considering the effect of the Na₂SO₄ concentration was established. Combined with the test data, the model was verified and the result was good. Under the action of Na₂SO₄ corrosion, Ca²⁺ in calcite and Fe²⁺ in hematite were dissolved and precipitated. With the gradual increase of Ca²⁺ and Fe²⁺ concentration, the damage variable increased gradually. The relationship between the two ion concentrations and the damage variable approximately satisfied a linear function.