Failure mechanisms and compensation support technology of deep high-stress soft rock roadways

Stress redistribution of deep excavation rock mass is a complex mechanical problem of multiple stresses. First, the mechanical model of surrounding rock at the moment of excavation of deep high-stress soft rock roadways was established based on the superposition principle of elastic theory, and the variation rules of tangential stress σ₁ and radial stress σ₃ were studied. Then, the supporting mechanical model of deep high-stress soft rock roadways was constructed, and the supporting effect of surrounding rock was revealed. Next, the response characteristics of σ₁ and σ₃ of surrounding rock and corresponding failure mechanisms under traditional support and compensation support were investigated through physical model tests. Finally, the applicability of compensation support technology was verified by numerical simulation and field engineering application. Mechanical analysis results indicated that the stress redistribution in deep high-stress soft rock roadways shows the trend of radial pressure relief and tangential pressure increase, σ₁ becomes twice of the original and σ₃ decreases to 0 at the moment of excavation. After supported the excavated rock mass, the σ₃ of roadway edge is the support resistance of surrounding rock, and σ₁ decreases with the increase of support resistance. The model test results showed that surrounding rock deformation of compensation support reduces by 73.7%, the destroyed area reduces by 88.3%, the crack length reduces by 11.0%. The σ₃ of the shallow surrounding rock increases by 68.3%, and the peak value of σ₁ decreases by 18.2%. The compensation effect of traditional support is weak, the σ₃ attenuates greatly and the σ₁ concentrates highly, which causes the crack to continue to open and extend in depth, resulting in the surrounding rock expansion deformation. Compensation support gives full play to the three-axis strength of the surrounding rock and mobilizes the self-bearing capacity of the deep rock mass by NPR cable. The compensation degree of σ₃ is high and σ₁ is significantly reduced, thus restraining the propagation and penetration of crack and realizing the self-stability of surrounding rock. After the compensation support technology is used in soft rock roadways, the NPR cables achieve constant resistance, the deformation of surrounding rock and the damage degree of support are significantly reduced, which indicates that this technology has a good control effect on deep soft rock engineering with high in situ stress.