Deformation And Reinforcement Mechanism Of Fractured Rock Mass Under Grouting And Its Application

The influence of cracks on the structural stability and mechanical properties of rock mass is very important.The deformation law and reinforcement performance of fractured rock mass under the action of grouting play a key role in engineering safety.In China,fractured rock mass is one of the most critical factors inducing instability and water inrush in underground engineering.The deformation and reinforcement mechanism of fractured rock mass under grouting has become an important scientific problem to be solved.Through the combination of theoretical analysis,numerical simulation,laboratory test and field test,the pressure distribution and rock mass deformation law of fractured rock mass grouting process are obtained,and the calculation method of shear strength of structural plane under different failure modes and filling degree is proposed.Finally,the calculation model of fractured rock mass strength after grouting reinforcement is established,and the research results are applied to the grouting reinforcement project of Qingdao metro fractured rock mass to verify and improve.The main results are as follows:(1)Aiming at the deformation law of fractured rock mass under grouting,a fluid-solid coupling slurry pressure distribution equation was established.According to the two-stage theory of unloading and reloading,the distribution equation of slurry diffusion pressure in fractured rock mass is derived by the relationship between continuous equation and mass conservation equation,and the displacement deformation law of fractured rock mass is obtained.For a single fracture,the diffusion distance increases with the increase of the gap width,and the smaller the gap width,the higher the sensitivity to the grouting pressure.For parallel cracks,the maximum deformation position of the smaller crack changes,and the value increases by 5 times.(2)Based on the theory of micro-convex and filling degree,the formula for calculating the shear strength of the structural plane of a single fractured rock mass is established.Aiming at the strength of single cracked surface reinforcement,according to the adhesion between the shearing surface and the sheared surface,the shear strength calculation formulas of sliding,shearing and breaking of the cracked structural plane under different normal stresses are established.Considering the influence of filling degree on the structural surface,according to the relationship between filling degree and shear strength,the formula for calculating the shear strength under filling is proposed,and it is found that the shear strength reaches the maximum when the filling degree reaches 0.2.(3)Using the Discrete Fracture Network Method(DFN),the overall strength calculation model for fractured rock mass is established by the fracture frequency.Based on the Hoek-Brown and Mohr-Coulomb strength failure criteria,a numerical model of grouting reinforcement strength of fractured rock mass is established by means of discrete element flow program(PFC).The results show that the gradual development of the cracks after reinforcement is similar to that of the unreinforced,but the failure mechanism is obviously different,and the strength is obviously increased.At the same time,the reinforcement strength decreases with the increase of the fracture frequency,and the cohesion c and the internal friction angle ? also follow.(4)Based on the reinforcement project of Ren Huitang Station of Qingdao Metro Line 4,the applicability of deformation and reinforcement mechanism of fractured rock mass under grouting in practical engineering is studied.The measured results and theoretical and simulation results of grout diffusion range,rock mass deformation and strength of fractured rock mass are compared and analyzed.The results show that the location,deformation range and overall strength of grout stone in fractured rock mass can meet the practical engineering needs within the allowable error range.