Investigation On The Grout Propagation Mechanism Of Curtain Grouting In Fractured Rock Mass In Deep Mines And Mining Influence On The Grout-Rock Composite

When metal mining reaches deep levels,it poses challenges to the“three high”complex geological environment,namely high ground temperature,high ground stress,and high rock solution water pressure.The disturbance caused by mining the ore body is very likely to trigger a high potential energy water inrush disaster.Many large-scale metal deposits in the southwest region of China are located in strong karst aquifers.Mining activities directly expose or excavate overburden fractures that connect large concealed water-conducting structures,which can induce water inrush disasters.Blocking the water-conducting channels in fractured rock masses through curtain grouting technology is an important way to actively prevent and control the risk of water inrush hazards caused by deep mining in mines.This thesis is supported by the National Natural Science Foundation of China（NSFC）under the projects of“Mechanism of Deflection Propagation for Grouting in Fractured Rock Mass with Flowing Water and Mining Influence on Grouted Curtain（42172293）”and“Investigation on the Mechanism and Prevention and Control of High Potential Energy Water and Sand Inrush Disaster Triggered by Mining and Excavation（42130706）”.This thesis focuses on three key scientific issues:（1）Mechanism and model of slurry flow diffusion in curtain grouting of fractured rock masses in deep mines;（2）Deformation and failure mechanism and instability criteria of the“slurry rock”combination under mining and seepage stresses;（3）Risk assessment model for water inrush after regional curtain grouting transformation,and the zoning evolution mechanism.This study is conducted using field surveys,measured data,theoretical analysis,model experiments,and numerical simulations.The main research results obtained are as follows:（1）The regional geology,structural development,hydrogeological characteristics of the Maoping lead-zinc mine were systematically analyzed.Two types of hydrogeological structures were classified,namely the“strongly water-rich aquifer lateral water filling—steep dipping type”on the western flank of the Shimenkan anticline and the“moderately water-bearing karst roof and floor water filling—gentle dipping type”on the eastern flank of the Shimenkan anticline.The main water-controlling characteristics of the two hydrogeological structures were analyzed.（2）Statistical analysis was conducted on the development law of joint fissures in mining rock masses,and the development direction of dominant joint fissures in the mine was obtained.A three-dimensional fracture network model was reconstructed.The core of the curtain axis is broken,and high-angle joints and fractures are developed,about 80%of the joints and fractures have dips between 65°and 85°,with an average dip of 68.5°;the tendency is mainly developed along the two dominant directions,which are 120°～160°and 260°～280°,respectively.Using the Monte Carlo simulation method and selecting the Fisher random model,a random elliptical three-dimensional fracture network model with dimensions of 30×10×10 m was established,and the resulting model was superimposed to reconstruct the three-dimensional fracture network model of the Maoping Lead-Zinc Mine rock mass.（3）Based on the principle of least action of slurry movement,a theoretical model of the“bias flow effect”of slurry in rock fractures has been established.On all potential diffusion paths of grout in rock fractures,it will first diffuse along the path that consumes the least energy,i.e.min(?E_R1,?E_R2,?E_R3,?E_R4,……).Therefore,this diffusion path is the"biased flow"path of grout,which is the theoretical model of“biased flow diffusion”of grout.Analyzed the flow distribution law of the herringbone intersection fracture and defined the“slurry heterogeneous diffusion strength indexΓ”.The concept of grouting can provide reference for the design and construction of mine curtain grouting.（4）A similarity model was established for the mining influence of the grout-rock composite of mining curtain grouting,and the stress-strain and displacement evolution laws of the surrounding rock and the grout-rock composite under mining disturbance were obtained.The grout-rock composite of grouting curtain presents a state of three-segment tensile strain and three-segment compressive strain interval distribution.As the influence of mining stress gradually strengthens,the frequency and intensity of vibration disturbance significantly increase.From the perspective of stress fluctuation amplitude,it roughly shows a pattern of greater stress fluctuation amplitude with greater burial depth,and the stress evolution of the rectangular structure tip is more stable compared to the triangular structure tip,which is more conducive to improving the anti mining failure ability of the grouting curtain.The mining of the ore body does not have a significant impact on the hydrogeological structure of the mine,and the main aquifer,impermeable layer,and grouting curtain grout-rock composite will not break or lose stability.（5）Based on the fiber-optic monitoring system of the grouted curtain body and the microseismic monitoring system in the mining area,we analyzed the stress evolution process of the curtain grout-rock composite and the judgment of mining seepage instability under the combined effect of the mining disturbance stress and the high osmotic pressure difference between inside and outside of the curtain.Large oscillatory fluctuations in tensile and compressive strains were monitored in the depth range of 140～206 m in the northern curtain of the Maoping lead-zinc mine,indicating that the curtain body was subjected to significant mining shear stress.The northeastern part of the northern curtain and the western part of the southern curtain were gradually touched by microseismic events,forming a localized belt distribution,indicating that the mining activities disturbed the surrounding rocks in these two directions of the curtain body,resulting in more microfracture events in the grout-rock composite.The overall destabilization safety coefficients F_Sof the north side grouting curtain and south side grouting curtain of Maoping lead-zinc mine under the combined action of mining and seepage are 2.51～3.25 and 2.85～3.49 respectively,which indicate that the overall stability of the curtain body is high,and large-scale destabilization damages basically won’t occur.（6）The minimum deviation comprehensive assignment model for the evaluation of water-surge risk in metal mines was constructed,the comprehensive weights of the main control factors were calculated,and the water-surge risk of each main mining middle section before/after the implementation of curtain grouting project was classified into five grades,namely,safety zone,relative safety zone,transition zone,relative danger zone and danger zone by the natural grading method within the Arc GIS system,and on-site investigations were carried out for validation,which proved that the evaluation results were accurate and reliable.From the average value of each major middle section of Maoping lead-zinc mine,curtain grouting increased the percentage of safe zone by 16.86%,decreased the percentage of relative safe zone by 3.69%,decreased the percentage of transition zone by 8.40%,decreased the percentage of relative hazardous zone by 1.37%,and decreased the percentage of hazardous zone by 3.40%.This thesis analyzed the impact of curtain grouting on the risk of water inrush in mines and the mechanism of zoning evolution from four aspects:weakening the hydraulic connection inside/outside the curtain（water source control）,grouting to enhance structural water resistance（pathway sealing）,improving the hydrodynamic environment inside the curtain（drainage and pressure reduction）,reducing mining induced rock damage（filling mining）.There are 92 figures,30 tables,249 references in this thesis.