Study On The Clogging And Filling Mechanism Of Coarse-grained Soil And The Repair Of Clay Soil Crack

The dam with coarse-grained soil as the main source is prone to particle migration due to its large permeability.Particle migration can block the pores of the soil in the dam foundation and reduce the leakage of the soil in the dam foundation.In addition,the core wall with cohesive soil as the main anti-seepage material often appears penetrating cracks due to extreme temperature difference,uneven settlement and other reasons,which induces seepage failure.Under the protection of the filter layer(coarse-grained soil),hydraulic filling and clogging can effectively repair cracks.Therefore,it is of great significance to study the clogging of coarse-grained soil and the repair of cracks for the safe operation of hydraulic structures.In this paper,through the method of seepage theory combined with laboratory test,the effective pore theory of natural soil is introduced to deduce the clogging theory of coarse-grained soil,and compared with the indoor seepage clogging test.The factors affecting fine particles in coarse-grained soil and the characteristics of particle migration are studied.The deposition law and penetration characteristics of fine particles in coarse-grained soil are analyzed,and the clogging situation,hydraulic gradient and pore change characteristics before and after clogging are studied.The effects of muddy water concentration,water head,seepage direction(i.e.,horizontal,vertical,oblique)and non-uniformity coefficient of filter layer on fracture repair were systematically studied.The motion state of fluid in fracture during fracture repair was determined,and the evolution law of fracture under muddy water seepage was studied based on digital image processing technology.The main achievements are as follows:(1)The permeability of coarse-grained soil after filling is related to the particle composition of coarse-grained soil,the porosity of filling material and the particle size of filling material.On the basis of previous studies,the expression of permeability coefficient of natural coarse-grained soil after filling is derived theoretically.(2)The main factor affecting the migration of fine particles in coarse-grained soil is the particle size ratio,and its retention law conforms to the Peak-Gauss function relationship.The migration characteristics of fine particles in coarse-grained soil can be described according to the particle size ratio interval.The penetration law of fine particles satisfies the Logistic function relationship,which can directly predict the internal clogging of coarse-grained soil.The particle size ratio is the main factor affecting the clogging and hydraulic gradient in each model,followed by the influence of water head.When the particle size ratio is less than 13.10,the clogging ratio decreases with the increase of particle size ratio,and the hydraulic gradient increases with the increase of particle size ratio.When is greater than 13.10,the clogging ratio increases with the increase of particle size ratio,and the hydraulic gradient decreases with the increase of particle size ratio.The degree of clogging in coarse-grained soil is closely related to the change of porosity.The degree of clogging can be judged according to the change of porosity in coarse-grained soil.(3)Under the action of muddy water seepage,the fracture repair process can be divided into three stages : transition period(stage 1),repair period(stage 2)and stable period(stage 3).Muddy water concentration,water head,crack form and uneven coefficient of filter layer are the main influencing factors of crack repair.The time required for crack repair is the shortest under high concentration and low water head.The fracture repair process will affect the seepage characteristics of the fluid in the fracture.The fluid motion law in stage 1 and stage 2 satisfies the Forchheimer flow,and the fluid motion law in stage 3 conforms to the Darcy flow.The starting point of stage 3 is the critical point of flow transition,and the stage of fracture repair can be judged according to the change of flow state in the fracture.The seepage quantity Q and flow velocity v after crack repair are significantly lower than those before repair,and the hydraulic gradient J is significantly increased,indicating that the permeability resistance of the soil after repair is basically restored.