Abstract: The dam anti-seepage body with cohesive soil as the main source often has perforated cracks due to extreme temperature difference, uneven settlement and other reasons, which eventually induces seepage failure. Hydraulic filling and clogging is an economical and effective repair method. In order to understand its repair mechanism, this paper takes the remolded cohesive soil as the research object, prefabricates cracks in the soil to simulate the cracking of the impermeable body, and studies the effects of muddy water concentration, water head, seepage direction (i.e. horizontal, vertical, oblique), non-uniformity coefficient of the filter layer and other factors on crack repair. The motion state of the fluid in the crack during crack repair was determined, and the evolution law of the crack under the action of muddy water seepage was studied based on digital image processing technology. The results show that under the action of muddy water seepage, the crack repair process in cohesive soil can be divided into three stages: transition period (stage 1), repair period (stage 2) and stable period (stage 3). The crack repair process will affect the seepage characteristics of the fluid in the crack. The fluid motion law at stages 1 and 2 satisfies the Forchheimer flow, and the fluid motion law at 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 crack. Muddy water concentration, water head, crack type 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 muddy water concentration and low water head. The seepage quantity Q and flow velocity ν after the crack repair are significantly lower than those before the repair, which are reduced by 99.83% and 99.98%, respectively, while the hydraulic gradient J is significantly increased by 27.92 times, and the impermeability performance of the soil after the repair is significantly enhanced. The research has certain theoretical guidance value for the evolution mechanism and prevention measures of the cracks in the dam anti-seepage body.

Key words: muddy water, perforated cracks, hydraulic filling, digital image processing, impermeability performance