Study on the mechanical properties of fractured anchored body under hydrostatic pressure

Taking the anchored body on the water-facing side of the coal pillar as the research object, and the water-facing side of the anchored coal body is generalized into a uniaxial stress model for the shallow fractured anchored body and a triaxial stress model for the deep fractured anchored body. Mechanical property tests of anchored fractured samples under hydrostatic pressure are conducted. The results show that, the mechanical properties of fractured samples are enhanced under the anchoring effect of the bolts. The anchoring reinforcement rates for the peak strength and residual strength of the fractured samples are 0.18 and 0.51, respectively. However, the effect is weakened by hydrostatic pressure, with the anchoring reinforcement rates decreasing by 7.3% and 18.8%, respectively. Through case analysis, the strength degradation mechanism of anchored fractured samples under hydrostatic pressure is revealed. Based on this, a two-dimensional GDEM numerical model of anchored fractured samples is established to investigate the influence of bolt pre-tension on the mechanical properties of fractured samples under hydrostatic pressure. With the increase in bolt pre-tension, both the peak strength and residual strength of the anchored fractured samples gradually improve, with the enhancement effect on residual strength being more pronounced than that on peak strength. High pre-tension suppresses fracture development in the loaded samples, leading to a reduction in the permeation zone range during the residual strength stage. Under triaxial compression conditions, the control effect of the bolts on fracture development is weaker than that of the confining pressure, resulting in minimal changes in the permeation zone range as the bolt pre-tension increases.