Research On Propagation Characteristics Of Fracture Grouting In Clay Formation

With the development of transportation in China,the construction scale of tunnel and underground engineering is getting larger and larger.Affected by bad geological bodies such as joints,fissures,faults and karsts during construction,it is easy to induce disasters such as sudden mud gushing,which seriously threatens the safety of construction personnel and machinery.As a method of geotechnical reinforcement and waterproofing,fracture grouting is widely used in the prevention and treatment of geological disasters.However,the research of fracturing grouting propagation lags far behind the engineering practice.This paper focuses on the problems existing in the research of fracturing grouting propagation,and systematically studies the process of fracturing grouting propagation and the shape of grouting veins in homogeneous and heterogeneous layers by means of experimental design and numerical modeling.The main research contents and results are as follows.(1)The optimal ratio test of cement-based stable slurry was carried out,and the discriminant standard of cement-based stable slurry was put forward.The ratio of stable slurry was obtained by comparing the variation of slurry density,water yield and viscosity.Triaxial tests were carried out on kaolin and gypsum-clay to study the laws of cohesion,internal friction angle and initial modulus of different injected media,and to obtain the model ratio.(2)A two-dimensional grouting test system was developed independently,and the grouting propagation test of homogeneous and heterogeneous clay formations was carried out,focusing on the propagation characteristics of grout vein under different densities,water-cement ratios,soft and hard soils and fracture characteristics.The rules of groutvein propagation,morphology,earth pressure and surface uplift pattern were obtained.It is found that there are two types of grout veins in the homogeneous layer and three propagation modes in the soil.There are four types of grout veins in the uneven hard and soft strata.There is one form of grout vein in the fractured strata.There is a large increase in the earth pressure near the grout vein.When the grout vein is close to the surface,the surface accelerates the uplift.There are symmetric "convex" shape and asymmetric "convex" shape caused by different grout veins.(3)Using numerical simulation to further study the grout vein propagation characteristics,the density,modulus,cohesion and grouting pressure of the homogeneous layer as well as the soft and hard,stratification and fracture characteristics of the heterogeneous layer were simulated in 73 conditions.The variation rules of grouting pressure,soil stress field,displacement field,grout vein morphology and surface uplift are analyzed.It is found that the farther away from the grouting hole,the smaller the grouting pressure.The tensile stress area appears at the tip of the grouting vein and on the surface;Vertical grouting vein mainly causes horizontal displacement,while deflection grouting vein mainly causes vertical displacement.The simulation results of homogeneous layer showed two more types of grout vein morphology than those of experiment: vertical grout vein and v-shaped grout vein;The shape of heterogeneous layer is the same as that of experiment.The surface has symmetrical "concave" shape,symmetrical "convex" shape and asymmetric "convex" shape uplift.(4)In this paper,the mechanism of deflection of grout vein in soil stiffness and strength,weak contact and stress field is analyzed from the mechanical point of view.The results show that the upper hard and lower soft soil layer will cause horizontal deflection.The weak contact was pulled apart before the grout vein arrived,and the horizontal deflection appeared.The rotation of the local stress field of soil will cause the tilt deflection.Three mechanical mechanisms can work together when grout vein deflection occurs,but one of them may play a leading role.