Mechanism Of Grouting Diffusion And Reinforcement Of Rock Fracture Based On The Bleeding Effect Of Cement Slurry

The stability of engineering rock mass is significantly affected by the nature of fractured structural planes.The instability and damage of the engineering rock mass induced by the cracked structural plane seriously threatens the safety of the tunnel and underground engineering during the construction period.Grouting is one of the main methods to solve underground engineering disasters,which can effectively improve the stability of the engineering rock mass.Ordinary Portland cement is the most commonly used grouting material in grouting engineering,and the water separation characteristics of its suspension affect the rheology of the slurry.The fractured structural surface has obvious roughness and tortuosity,and this has a significant impact on the grouting diffusion process and the grouting reinforcement strength characteristics of the fractured rock mass.In this paper,laboratory experiments and theoretical analysis are used as the main methods to study the rheological changes of ordinary Portland cement during the entire water separation process.An analytical model was established to describe the apparent viscosity change of cement slurry during the process of water separation.Based on the geomechanical origin of the fracture structure surface,the fractures are divided into tensile rough fractures and shear rough fractures.A simulation experiment of grouting in rough cracks was carried out,and the influence of crack opening,crack roughness,and crack surface roughness on the grouting diffusion law was analyzed.The theoretical model and calculation method of grouting diffusion in rough fissures are established.The influence of crack roughness,grout filling thickness and the difference of the roughness of the crack structure surface and bottom plate on the shear mechanical properties of the grouting filling structure surface is further analyzed.The main work and innovation results are as follows:(1)Through indoor experiments,the change law of the density and rheology of ordinary Portland cement slurry with a water-cement ratio ranging from 0.8 to 2.0 was obtained during the entire water separation process.A Herschel-Bulkley fluid model considering water separation factors is proposed.(2)Based on the self-weight consolidation of cement slurry,the relationship between the water-cement ratio and the water-cement ratio,the relationship between the apparent viscosity of the slurry and the water-cement ratio.An analytical model is proposed to describe the apparent viscosity change of cement slurry during the entire water separation process.The model successfully described the two-stage growth law of the apparent viscosity of the slurry during the entire water separation period.(3)A set of rough fracture grouting simulation test system has been developed.The test system is composed of a constant rate grouting system,a rough fracture test platform,and a data monitoring system.The grouting diffusion simulation test with cracks of different roughness can be realized,and the variation characteristics of the grouting pressure and the pressure field of the diffusion zone during the grouting process can be accurately obtained.(4)The rock mass fractures are divided into tensile rough fractures and shear rough fractures.Based on the self-developed rough fracture grouting simulation test system,grouting simulation tests for tensile rough fractures and shear rough fractures were carried out respectively.The effects of crack opening,crack roughness and the difference in crack upper and lower surface roughness on grouting pressure,pressure field distribution in the grout diffusion zone and local pressure drop are obtained.(5)A theoretical model of grouting diffusion in rough cracks under the condition of constant grouting rate is proposed.Based on the step-by-step calculation method,the timevarying viscosity of the cement slurry after water separation is taken into account,and the complete calculation of the rough fracture grouting diffusion process is realized.(6)The shear mechanical characteristics of tensile and shear grouting structural surfaces are studied,and the shear failure characteristics of four common types of grouting structural surfaces are summarized.The influence of the roughness of the structural surface,the thickness of the grout filling and the roughness of the bottom wall of the structural surface on the peak strength,residual stress and shear strength parameters of the grouting filling structure is analyzed.Based on the shear mechanics model of tensile and shear grouting filling structural surfaces,the shear failure mechanism of grouting filling structural surfaces under different normal loads,structural surface roughness and grout filling degree conditions are revealed.