Abstract: The seepage induced by moving water and sand in composite slope in surface mine threatens the slope safety and surrounding environment. In order to reveal the interaction mechanism among sand particles under the action of seepage,with characteristic structure unit of sand clusters as object, we analyzed the process of nonlinear movement and deformation and mechanical behavior of the strong chain among sand particles under actions of gravity, buoyancy, normal and shear contact force and seepage force in particle size scale. Furthermore, we proposed a new plastic-to-hinge element to improve the Будин model and established a mechanical model of sand creep with elastic-visco-plastic hinge. According to model test of moving water and sand and data from sand creep test, we gave constitutive equation and creep curve equation of the model and identified the parameters of the improved Будин model and verified its accuracy. Results show that the model could describe the contact, friction and rotation among sand particles during creep process with good accuracy; secondly, the model reveals the graded ladder-like failure phenomenon in the water-sand layer and shear attenuation and non-attenuation among sand particles, as well as the positive and negative accelerating shear creep process in the third stage.The present model offers a new mechanical approach for analyzing the interaction mechanism among discrete particles.

Key words: surface mine, seepage induced by moving water and sand , composite slope, improved Будин model, sand creep