Research On Instability Mechanism And Stability Control Of Deep High-stress Soft Rock Large-section Tunne

The safety hazards of deep high stress soft rock large section roadways in underground mines are highlighted.This paper takes Jinfeng Gold Mine as the engineering background,This paper analyses the macroscopic physical properties and microscopic damage mechanism of high stress soft rock,explores the destabilisation mechanism,and provides a basis for roadway support by using field investigation,physical experiment,numerical simulation,theoretical analysis and field monitoring.The main conclusions are as follows.（1）The maximum principal stress value of 21.1 MPa was measured using the sleeve hole stress relief method,which indicates that the stress value increases linearly with depth.The RQD values are mainly in the range of 20%to 45%,with a rock rating of"bad".By plotting the structural surface poles and Schmidt’s isodensity diagram,it is statistically evident that the surrounding rock is densely packed with two dominant structural surfaces with a volume number（density）of 9.2 bars/m³.（2）A typical specimen was selected for triaxial compression and electron microscope scanning tests.It was found that the peak strength of the rock sample changed in a“spoon”shape as the dip angle of the interlayer increased.The influence of the structural surface decreases as the surrounding pressure increases.Under no lateral pressure conditions,significant tensile damage occurs in the 0°and 90°specimens,with damage to the mineral surface and fractures expanding around the pore.At 30°and 60°,both tensile and shear damage occur significantly,with damage to the mineral surface or weak areas,and cracks forming mainly around the mineral;at high lateral pressures,at 0°,30°,60°and 90°,significant shear damage occurs,large amounts of debris,and a heterogeneous distribution of microcracks,with damage to both the mineral surface and interior.（3）Factors such as structural plane and engineering background are considered,after the rock mass is reduced.The characteristics of the stress field,displacement field and plastic zone for different burial depths,lateral pressure coefficients and three-core arch section specifications were studied using FLAC^3D.The study shows that the volume increase of the plastic zone accelerates when the burial depth of the roadway reaches 700 m.When the burial depth exceeds 900 m the stresses in the roof of the roadway show multiple stress concentrations The increase of lateral pressure coefficient will increase the maximum stress value of the roof plate,and the stress concentration zone of both gangs occurs a large lateral expansion,and the damage pattern of the surrounding rock is relatively single and regular.The size of the roadway section has a great influence on the scope of the roof stress concentration zone.As the section area increases,the roadway is widely unstable,and the plastic zone volume increases at the fastest rate when the roadway section size is 7 m×7 m.（4）Taking the 150E roadway as the engineering background,the support parameters suitable for the deep high stress large section soft rock roadway were determined through the field situation and the combined arch theory,and the optimized support method of“reinforcement anchor+hanging net+increasing the thickness of slurry spray”was proposed.The numerical simulation shows that the optimised support can make full use of the deep surrounding rock to bear the stress of the roadway and improve the bearing capacity of the surrounding rock,the maximum deformation of the surrounding rock after the optimised support is 57%of the maximum deformation of the original support,and the volume of the plastic zone of the surrounding rock is reduced from 1039.45 m³ to 154.42 m³ after the optimised support.The deformation volume is similar to the numerical simulation results,which demonstrates the accuracy of the numerical simulation results and proves that the optimised support has a good control effect on the stability of the deep high stress soft rock large section roadway.