Hydrofracturing Effect In Rock Grouting

Grouting reinforcement of surrounding rock is a widely used technical means in mining engineering and geotechnical engineering.With the gradual lack of shallow coal resources,the exploitation and utilization of coal resources has gradually developed to the “three depths”,and a large number of deep mines have emerged.In the grouting activity of low-permeability deep soft rock under high ground stress and strong mining dynamic stress,the conventional grouting method without splitting cannot achieve effective reinforcement due to the limited range of slurry penetration.However,there is little research on the mechanism of high pressure fracturing grouting under true triaxial stresses conditions.Therefore,the core scientific problem of fracturing effect in rock grouting is studied by means of physical experiment and theoretical analysis.On the basis of 4000 kN true triaxial experimental framework,a “water-slurry” conversion device was designed and manufactured independently to form a true triaxial grouting experimental system.Under the engineering background of deep high-stress soft rock grouting,the neoprene latex cement mortar with reasonable proportion was used as the similar material to simulate deep soft rock,the basic mechanical properties of the standard samples were tested and their similarities were demonstrated from the basic mechanical properties.The experimental study of conventional grouting and fracturing grouting under a given stress environment was carried out using a true triaxial grouting experimental system.The experimental results show that there is no splitting crack in conventional grouting under true triaxial stresses condition,and the grout permeability and diffusion range is ellipsoid,which is centered at the center of the bare hole segment with the axial and radial axis of the sealing device as the long and short axis on the plane parallel to the maximum principal stress.In the fracturing grouting experiment,according to the variation of grouting pressure,the process of fracturing grouting is divided into two stages: the generation and propagation of splitting grouting and the seepage equilibrium stage of cyclic opening and closing of splitting cracks after the splitting crack propagation is completed.In the generation and propagation of fracturing grouting,with the continuous expansion of splitting cracks,the grouting pressure increases step by step when the main splitting occurs.In splitting grouting under true triaxial stresses conditions,a single split is still perpendicular to the direction of the minimum principal stress.According to the shape of the slurry and its distribution on the fracture plane,the fracture plane is divided into four zones: macroscopic splitting zone,micro-splitting zone,seepage pressure zone and unwetted zone.The splitting crack is composed of the macroscopic splitting zone and the micro-cracking zone,which are separated by a macroscopic splitting front.According to the spatial shape of the splitting crack in the splitting grouting under the true triaxial stresses condition and the slurry infiltration and diffusion form in the plane of the splitting crack,combined with the stress state analysis around the grouting borehole under the action of in-situ stress field,the mechanical model of rock drilling grouting splitting in two-dimensional plane(perpendicular to the intermediate principal stress)is established.According to the law of energy conservation,the energy transformation in the process of rock grouting splitting expansion is analyzed from the perspective of energy dissipation,and the calculation methods of splitting pressure and spreading pressure in the process of rock grouting are obtained.The orthogonal experimental method was used to study the influence of main influence factors such as main stress difference,pumping displacement and slurry water-cement ratio on the fracturing effect in rock grouting.The variation of splitting pressure and expansion pressure,the number of acoustic emission events and energy,the plane smoothness of splitting fracture and the distribution of slurry diffusion form are obtained under the condition of changing the above factors.