Damage evolution model of sandstone under coupled chemical solution and freeze-thaw process

In the rock engineering of cold region eroded by chemical solution such as groundwater and acid rain, the pore development law, damage degree and failure characteristics of rock are closely related to the coupling effect of chemical solution and freeze-thaw. The freeze-thaw cycles of sandstones in different chemical solutions are experimented. The pore variation law and damage evolution mechanism of sandstones immersed in different chemical solutions are studied by means of nuclear magnetic resonance (NMR). The sandstone samples are placed in acidic solution, alkaline solution, neutral salt solution and aqueous solution for freeze-thaw cycling test. The composition, porosity change and T2 curve change of the samples are analyzed. The results show that the porosity of sandstone samples increases with the increase of the number of freeze-thaw cycles under the coupling of chemical solutions and freeze-thaw cycle. After 40 freeze-thaw cycles, the change rate of porosity is from large to small: neutral NaCl solution, H2SO4 solution, NaOH solution, aqueous solution. The pore sizes of all the samples affected by the coupling of chemical solution and freeze-thaw are mainly concentrated in two sizes, and the larger pore size is dominant. In neutral NaCl solution, chemical corrosion and freeze-thaw effect promote each other and play a superposition effect. In H2SO4 and NaOH solution, the superposition effect of chemical corrosion and freeze-thaw effect is inhibited to a certain extent. At the same time, according to the variation law of sample porosity in different chemical solutions, the quantitative expression of damage variable of the sample is obtained, and the damage evolution model of sandstone is derived.