Experimental And Numerical Study On The Diffusion Laws Of Cement Grout In Rough Rock Fracture

In the development of infrastructure construction all over the world,the mountain tunnels have been developed as an effective way to traverse mountainous areas and to improve the traffic convenience.However,due to the complex geological and hydrological conditions in lots of mountainous areas,geological disasters such as gushing water are extremely likely to occur during the tunnel excavation,which has brought great difficulties to the construction of mountainous tunnels.In particular,inrush water disasters that occur in fractured zones and rough fracture rock masses will not only cause tunnel collapse,but also cause casualties,significantly increasing construction costs and delaying tunnel construction.Grouting is a method of injecting cementitious grout materials such as cement grout into fractured rock masses and other weak strata.This method aims to improve the mechanical and waterproof properties of rock masses by injecting grouting materials into voids and cracks in rock masses.Because the rock fractures are related to the fracture geometric aperture,the joint roughness,and the inclination angle of the cross fractures,the diffusion laws of the grout in the rough rock fractures are different from that of the general grouting.And its diffusion mechanism is not clear at present.Moreover,due to the concealment of the grouting process,it is usually difficult to detect the movement of grout in the rock mass fractures,and the effectiveness of grouting for water plugging and for rock mass reinforcement is difficult to evaluate.In this paper,the large-scale laboratory grouting tests and numerical simulations were conducted to investigate the diffusion of the cement grout injected into different rough rock fractures.The main research contents and conclusions of this paper are as follows(1)The pressure gradient and flow rate within a single fracture were investigated by large-scale laboratory grouting tests using a rough single fracture model.The cement grout injected into a single fracture was also analyzed by considering the characteristics of the fracture aperture,JRC range and injection pressure.The results show that the fracture surface roughness and injection pressure are positively correlated with the pressure gradient.The fracture aperture is negatively correlated with the pressure gradient of cement grout.Therefore,it is believed that the rougher the fracture surface is,the greater the influence on the diffusion range of the cement grout is,and the difficulty of grouting is increased.(2)The single fracture grouting model was established by using the multi-field coupling software COMSOL,and the numerical calculation was carried out.The effects of fracture aperture,injection pressure,JRC range,and groundwater on the grout diffusion laws were comprehensively considered.The numerical results and experimental results have a consistency in the change laws.The diffusion laws of cement grout in single fractures containing groundwater were further studied,and the change law of cement grout and groundwater in single fracture with grouting time are obtained.(3)The diffusion law of the cement grout injected into the Y-shaped cross fracture was investigated by performing numerical simulations.And the influence of inclination angles and JRC ranges on cement grout diffusion were considered.The results show that the pressure gradient,flow rate,and Reynolds number of the Y-shaped cross fracture are smaller than those of the single fracture.And as the inclination angle of the Y-shaped cross fracture increases,the flow rate of cement grout gradually decreases.