Grouting Filling And Mechanism Of Dynamic Water Plugging In Coastal Karst Structure And Engineering Application

Karst geology is widely distributed in China,and many coastal urban areas are in karst development areas.Karst structures such as karst caves,karst trenches,karst troughs,and dissolution fissures are highly catastrophic.It is very easy to induce geological disasters such as water inrush and karst collapse in the process of mineral resource mining,underground space development,and infrastructure construction,which seriously threaten the safety of people's lives and properties,and have become an important issue restricting the engineering construction of coastal karst areas.The Hepu limestone mine of China Resources Cement,Beihai City,Guangxi Province is mined in an open-pit recessed type.The karst structures are widely distributed in the mining area and have strong hydraulic connectivity.With the mining of mines,the number of exposed water gushing points has gradually increased,leading to large-scale water gushing in the mines,inducing major secondary disasters such as the large-scale ground collapse in the mining area,deformation,and settlement of surface structures,and bringing great challenges to the safe production of mines and the construction of green mines.The difficulty of its treatment is mainly reflected in two aspects:on the one hand,how to realize the filling and reinforcement of the shallow karst structure area,in which the research and development of effective grouting filling materials and the long-term stability of the reinforcement are the main problems to be solved.On the Other hand,how to achieve dynamic water grouting plugging of deep water-conducting structures,and the study of the related plugging mechanism under the action of tides has important theoretical value for actual engineering grout selection,grouting parameter determination,and grouting process optimization.However,these two aspects are rarely studied when considering the effects of coastal tides.In response to the above problems,this paper uses scene investigation,laboratory experiment,theoretical analysis,numerical simulation,and engineering application as the main research methods,puts forward the coastal karst development model,constructs the coastal karst basic geological model.The research,development and performance research of grouting filling materials for karst structures have been carried out,which has realized the effective filling of shallow karst structures,and its long-term stability have further analyzed.Physical simulation experiments and numerical simulations were used to study the mechanism of dynamic water grouting in coastal karst structures,and grouting control methods were proposed,which were applied in the Hepu Mine Water Control Project.The main research work and results of this paper are as follows:(1)The characteristics and influencing factors of coastal karst development were studied,and the analysis of hydrodynamic characteristics of coastal karst areas was carried out.On this basis,through a comprehensive analysis of underground hydrodynamic characteristics,geological structure,rock elements,rock microstructure,and rock minerals of Hepu Mine,the typical development pattern of coastal karsts has been identified.A geological model of coastal karst controlled by the combined action of faults and tides has been established,and the main controlling factors for the development of coastal karsts in the mining area have been determined.(2)The compatibility characteristics of limestone tailings with steel slag,fly ash,and blast furnace slag were determined,and the design method of limestone tailings-based cementitious material was proposed.By establishing a nonlinear mathematical model between mechanical strength and various components,the effective control of the mechanical strength of the cementitious material was realized.It reveals the influence mechanism of limestone tailings sand fineness modulus,mortar sand ratio,and slurry concentration on fluidity,strength,and pore structure.Considering the economy of the filling material comprehensively,the control parameters for the preparation of the filling material was proposed:fineness modulus 2.91,slurry concentration 83%,and mortar ratio 1:5.The influence of tidal action and seawater erosion on the mechanical strength of the filling material was determined.Because SO42-and Cl-have salt activated effect on the filling material,the mechanical strength of the filling material showed an upward trend under the two curing conditions.(3)Limestone tailings-based filling materials have good cementation compatibility with rock and soil in coastal karst areas.The strength of the reinforced body gradually increases with the extension of the curing age,and the pattern transition law of the reinforced body from shearing to tensile failure was determined.Through the numerical analysis of the long-term stability of the reinforced body of coastal karst structures,when the intersecting karst pipes and karst caves were filled,the final deformation of the ground surface and the deformation stability time decrease,while the grouting filling effect has more significant in the seawater environment.(4)The "caissons type" coastal water dynamic grouting simulation test system was developed,and the numerical simulation of dynamic water grouting under the tide was carried out by using the sequential diffusion and solidification method.The sealing mechanism of dynamic water grouting under the action of tide was revealed,and the control method of dynamic water grouting was established.Based on the geological survey and hydrogeological data,a three-dimensional geological information visualization model of the Hepu mining area was built,and the key water-conducting dissolution fissure area was generalized.Dynamic water grouting simulation analysis was carried out,and the Hepu limestone mine water control project was instructed.(5)The research results have been successfully applied to the grouting filling treatment of coastal karst structures at the Hepu mine site.Through long-term inspection and monitoring of the treatment area,the effectiveness of the grouting filling and plugging methods of coastal karst structures has been verified,and the No.2 water gushing point of Hepu Mine was successfully controlled.The total water reduction reached 46500 m3/D.