In order to analyze the dynamic evolution process of the soil arch behind anti-slide pile

a novel type of soil mass relative deformation monitoring system was designed

and a series of physical model tests was conducted. Two dimensionless parameters were introduced based on the monitoring data in the tests

for characterizing the relative deformation degree and uneven deformation degree of sliding mass. Some findings were observed. The evolution process of soil arch can be divided into three stages based on the curve characteristics of soil arch deformation and lateral thrust behind piles: elastic formation stage

plastic development stage and failure stage. And significant three-dimensional failure characteristics were observed in failure stage: on the horizontal plane

the soil arch exhibited layered arch ring extrusion failure; on the vertical plane

the soil in the middle parts of sliding mass first cracked and collapsed

and then a catenary-shaped crack appeared on the top of sliding mass. The strength parameters of the sliding mass around piles were in a dynamic strengthening process in the sliding process with the change of relative deformation. As far as the degree of strengthening was concerned

cohesion was more sensitive than angle of internal friction. The relative deformation degree and parameter strengthening degree of the sliding mass relatively backward in the early stage were higher than those of the sliding mass relatively forward. Therefore

the cracks in the sliding mass around the piles gradually deflected towards the center line between the piles in the process of cracks developing backward

and formed a stable supported arch structure after the cracks coalesced.