Mechanical Properties of the Hard Sandstone Fracture Surface under Hydrochemical Corrosion

Abstract

To realize a quantitative expression of change laws of the fracture surface shear strength with hydrochemical damage and to obtain optimal weakening effect of solution on the fracture surface strength, hard roof sandstone specimens containing hydraulic fracture surfaces from the Tashan Coal Mine located in Datong were subjected to a shear test after corrosion using solutions at different concentrations. The relational expression between shear strength and porosity of the fracture surface was established, and new damage parameters were introduced to describe the evolution laws of the shear strength of sandstone specimens with change in test conditions. Results were as follows. (1) Under sealed hydrochemical environment, corrosion effect on sandstone strengthened, and porosity and roughness gradually increased with increasing solution concentration and soaking time. (2) At a solution concentration of 3%-10%, shear strength and roughness of the fracture surface initially increased and then decreased. Hydrochemical solution concentration and action time were important factors that caused strength attenuation of the fracture surface. (3) When the solution concentration was greater than 3%, the roughness of the fracture surface increased with corrosion time, but its strength showed the tendency to stabilize. The shear strength of the fracture surface increased with shear displacement at a concentration of 5%. The study results can provide a new idea for strong strata pressure control through ground hydrofracturing hard roof.

Evolution of Peak Shear Strength of Rock Fractures Under Conditions of Repetitive Dry and Wet Cycling

“…Several studies have indicated that the peak shear strength of dry fractures is usually greater than that of saturated fractures when other conditions are the same (e.g., Pellet et al, 2013;Zhao et al, 2017;. Compared with a pure water environment, the peak shear strength of sandstone fractures further decreased by 25.5 and 43.2%, respectively, when the ionic concentration of a hydrofluoric acid (HF) pore solution concentration was 1 and 3% (Xia et al, 2019). The time duration of soaking in water also affects the shear mechanical properties of rock fractures.…”