Experimental Study On Seepagecharacteristics Of Grouting Fluid In Micro-fissures

Grouting technology is a widely used and practical engineering technology,which is of great significance to improve rock mass structure and stability.Due to the excavation of underground engineering,the distribution of cracks in rock mass is complicated.It is of great theoretical significance and engineering application value to correctly understand and grasp the flow law of grouting fluid in cracks for improving the effect of grouting on site.In this paper,a set of visualization model of micro-crack grouting has been developed,and a series of grouting seepage experiments of grouting with different crack openings and different cement particle sizes have been carried out by using this model.The flow law of different grouting in micro-cracks has been studied,and the theory of grouting velocity has been verified by numerical simulation.The research results are as follows:?1?A set of visual grouting test system with good sealing performance matched with high-speed micro-monitoring system is used.It is equipped with pressure and flow monitoring system,which can monitor the flow rate and pressure difference.It can also realize the required crack opening by adjusting the thickness of the gasket between cracks?high precision,strong tension,not easy to break,high hardness?.The experimental model is placed in a high-speed micro-monitoring system to realize visual micro-observation,and the water injection test verifies the effectiveness of the system.?2?The rheological properties of three kinds of cement slurries with different particle sizes were studied.The results show that the viscosity of cement slurry decreases with the increase of water cement ratio and increases with the decrease of cement particle size.Under the same conditions,the viscosity of ultra-fine cement slurry is obviously higher than that of ordinary cement slurry;The optimum dosage of naphthalene water reducer is about 0.75%.It can effectively reduce the viscosity of cement slurry and improve the fluidity of cement slurry;Under the same water cement ratio,the smaller the cement particle size,the smaller the water evolution rate of cement slurry.?3?Based on the high-speed microscopic visual monitoring model of micro-fissure grouting fluid seepage,the micro-fissure grouting experiment was carried out.The results show that the process of forming filter bridge blockage at the fissure opening by cement particles can be divided into three stages:Particle aggregation?crescent shape??Particle accumulation?semicircle??Bridging?semicircle?.By adjusting the crack opening of grouting,the minimum crack opening b_min and the critical crack opening b_crit of three kinds of cement slurries are obtained.Statistical analysis of the accumulation law of cement particles in grouting process under two monitoring conditions shows that the state of cement particles passing through cracks at different crack openings and the characteristics of cement particles passing through micro-cracks at different scales can be obtained intuitively.When the grouting fissure opening is greater than the critical fissure opening,the grouting end time decreases with the increase of grouting pressure under a certain grouting pressure.?4?The consistency of theoretical deduction and numerical calculation results of slurry velocity is verified by theoretical deduction of grouting fluid flow law in single fracture with crack opening greater than critical crack opening and COMSOL Multiphysics numerical simulation.