Mechanical Mechanism And Control Method Of Fracturing Grouting For Argillaceous Fault

With the rapid development of transportation infrastructure,more and more tunnel and underground engineering are to be constructed in China.Unfavorable geology such as fault and karst which is easy to induce related geological disasters has become a serious threat to the safety of engineering construction,resulting in serious sasualties and economic loss.For practical purposes,the fracturing grouting method has been widely adopted to manage geological disasters and can be used to improve the strength and permeability resistance of surrounding rock.However,compared to the rapid development of engineering practice,the study on mechanics of formation and propagation,and reinforcement theory of fracturing grouting make slow progress,which has become a key factor that restricts the development of scientific and controllable fracturing grouting.Based on actual engineering and by adopting the methods of theoretical derivation,numerical simulation,model test and field test,this paper mainly focuses on the problem of fracturing grouting reinforcement for argillaceous fault,with the aim of promoting the scientific·and controllable development of fracturing grouting engineering.The mechanism of fracture formation,propagation and termination was clarified.The quantitative reinforcement theory based on the grouting parameters and the physical mechanical parameters of injected medium was developed.Furthermore,the control method of fracturing grouting for argillaceous fault including grouting pressure control,size control of fracturing path,parameters control of the solidification of grout and medium,grouting progress control was presented,which provide an effective theoretical framework for grouting scheme designs,and was successfully applied to the actual engineering finally.The main innovations of this paper are as follows.(1)Formation mechanism of fracture.By using the particle flow method that based on discrete element theory and the PFC numerical software,and taking into account the influence of fluid-solid coupling,the particle flow calculation model of fracturing grouting for argillaceous fault was established.The transient starting process of the fracturing path was captured from the microscopic angle.It was found that the failure type of fracturing was tensile failure due to the increase of tensile stress.The approximate formula of initial fracturing pressure was obtained.Furthermore,the influence of parameters of grouting and injected medium on the number and scale of the fracturing path is discussed.(2)Propagation mechanism of fracture.The classical hyperbolic model was adopted to characterize the deformation law of soil under the effect of grouring pressure.The initial compression and recompression model of soil were developed,respectively.With the interaction and dynamic characteristics of multi-sequence grouting taken into account for the first time,the generalized and mathematical dynamic models for fracture propagation were presented,respectively.The influence of the initial compression performance of soil,grouting parameters and grout parameters on fracturing path size and grout driving pressure,and the influnence of pre-sequence grouting on the following grout diffusion law were therefore analyzed.Moreover,the ? was introduced to characterize the sizes of solidified grout,and the calculation model for sizes of solidified grout and its criterion incuding "narrow-short type" and "wide-long type" were put forward.(3)Quantitative reinforcement theory of fracturing grouting.On the basis of the fracturing path size and by introducing the key parameters of grouting including grouting pressure into the existing simplified reinforcement model,injection rate of grout and grout viscosity,the reinforcement mathematical model of fracturing grouting was presented,which has been verified by the design of the corresponding fracture grouting reinforcement experiment.Therefore,the calculation goal of "how much grouting pressure,injection rate of grout,and grout viscosity,then how much physical parameters of solidification body of grout and medium can be obtained to reinforce the " is preliminarily realized.(4)In order to verify the correctness of the study on propagation mechanism of fracture,the simulation experiment on grout fracturing diffusion in argillaceous fault was conducted,taking into account the influence of dynamic water environment,stress loading and multi-sequence grouting.The fracturing grouting process is divided into four representative stages ?conversion of grout diffusion type ?saturation of primary and secondary fracturing paths ?formation of new fracturing paths and ?saturation of the following fracturing zone.The pressure characteristics of three typical grouting types including filling,filling-fracturing,fracturing-filling-compaction-fracturing were obtained,and the concept and definition methods of primary and secondary fracturing pressure were proposed,respectively.On basis of grouting pressure,soil pressure and seepage pressure field,the identification methods for reinforcement area and reinforcement process were put forward.(5)Based on the jiangxi yonglian tunnel,the application experiment of curtain grouting method for tunnel fault with a ratio 1:20 and dimensions of 8 m*4.5 m*5 m was conducted,to verify the feasibility of the curtain grouting method for reinforcing the argillaceous fault,which is the most large-scale experiment at home and abroad so far.The experiment has simulated the original grouting environment of the tunnel,and also the key steps such as the clean of gushed mud,tunnelface backfill,layout of wall for grouting and the implementation of the grouting.The excavation after grouting showed that the curtain grouting reinforcement cycle has formed withirn 0.4?0.45 m around the tunnel,which greatly improved the bearing capacity and stability of the surrounding rock,and the tunnel finally gone through successfully.Furthermore,the empirical formula for the safe thickness of the curtain grouting reinforcement cycle and the influence range of the grouting are obtained.(6)Control method for fracturing grouting in argillaceous fault.On basis of the study results in regard to the mechanics of formation and propagation,and the reinforcement theory of fracturing grouting,the control method of fracturing grouting for argillaceous fault including grouting pressure control,size control of fracturing path,parameters control of the solidification of grout and medium,grouting progress control was presented,which has been used to select related curtain design parameters,grouting parameters and grout parameters,and then applied to reinforce the weak surrounding rock of Yonglian tunnel from ZK91+330 to ZK91+355.Finally,the tunnel gone through successfully.