Study On The Control Mechanism Of Splitting Grouting Vein Diffusion In Soft Soil

With the rapid development of China ’s transportation industry,infrastructure such as highways,high-speed railways,and underground tunnels are growing,providing great convenience for people ’s daily travel.However,while providing convenience,there are also many hidden dangers.During the construction or use of these infrastructures,they often pass through weak strata,resulting in pavement cracking,surface subsidence,stratum subsidence,water and mud inrush and other disasters,which seriously threaten the safety of engineering construction personnel and daily travel people.Grouting is the main technical means to control geological disasters such as surface subsidence,stratum subsidence,water and mud inrush in tunnels.In the process of tunnel and highway construction or use,the method of curtain grouting is often used.Through the grouting veins in each grouting hole,the soil is split and overlapped with each other.By forming curtain rings around the tunnel and roadbed,the soil is reinforced and the effect of anti-seepage and plugging is achieved.However,in the actual project,the slurry splitting in the curtain grouting process is a black box operation,and it is difficult to observe and control the splitting direction of the slurry vein.The splitting of the slurry vein is difficult to diffuse according to the expected direction and length,and multiple grouting is often required.Therefore,it is particularly important to clarify the splitting law of the slurry vein during the splitting grouting process,the opening and splitting of the multi-sequence grouting slurry vein and the diffusion law for the directional control of the splitting grouting slurry vein.In this paper,based on the grouting project of K0～K60500 section in the goaf of JinanWeifang Expressway Project Section of Shandong Expressway Group,aiming at the problem of splitting grouting in the grouting process,a true triaxial grouting test system was developed,and the grouting physical simulation test under three-dimensional stress was carried out by using this system,focusing on the splitting and expansion law of single-sequence and multisequence splitting grouting veins.By means of numerical simulation,the splitting and expansion law of single-sequence splitting grouting veins is further studied,which makes up for the deficiency of physical simulation test.The specific research contents and results are as follows:(1)A set of true triaxial grouting test system was independently designed and developed,including true triaxial grouting test platform,triaxial loading unit,grouting unit and information acquisition unit.The system has the advantages of true triaxial loading,mesoscale,multivariate data acquisition during the test process,complete grouting veins obtained by excavation,simple operation,easy disassembly,adjustable loading pressure of 0-30 MPa and grouting pressure of 0-10 MPa.The physical and mechanical parameters of the test soil and the condensation characteristics of the slurry were tested.Through theoretical derivation and data fitting,the splitting criterion of soil multi-sequence grouting is obtained.(2)The multi-sequence grouting physical simulation test of soft soil under true triaxial loading conditions was carried out.The grouting P-Q-t curves under different conditions and the soil pressure change curves at different positions and directions were obtained and analyzed.The three-dimensional scanner was used to obtain the spatial and plane position and shape of the slurry vein.The position and shape of the grouting pipe,slurry vein and soil pressure box inside the model were reproduced by the three-dimensional modeling software SOLIDWORKS.The effects of pre-grouting duration,pre-grouting setting time,grouting flow rate and second principal stress on the splitting pressure,splitting direction,expansion distance and grouting vein width of post-grouting grouting veins under constant-speed grouting conditions were studied.Through analysis,the mechanism of slurry vein splitting expansion under different influencing factors is obtained.(3)The numerical simulation of single-sequence grouting under plane stress condition is carried out,and the real-time variation path of the splitting propagation process of grout vein is obtained.The variation law of the shape,propagation radius and splitting direction of the splitting grout vein under different grouting pressure and different principal stress difference under constant pressure grouting condition is studied,which enriches and improves the splitting propagation law of three-dimensional grouting grout vein under the same condition of small principal stress and second principal stress.