A model experiment of passive soil with limited width behind a rigid retaining wall was carried out using non-cohesive coarse sand

with the soil images during the experiment collected through a high-speed camera. In addition

the soil deformation and shear strain were analyzed based on the digital image correlation method to reveal the slip surface characteristics in 3 movement modes: translational mode (T mode)

rotate-about-top mode (RT mode)

rotate-about-base mode (RB mode). The results show that: the boundary value of width to height ratio (B/H) of soil with finite passive width is

B/H≤2.0 for T mode

B/H≤1.6 for RT mode and B/H≤1.1 for RB mode. In T mode

when 1.6≤B/H≤2.0

the passive slip surface is composed of two discontinuous fracture surfaces

the lower and upper fracture surfaces start from the heel of the moving retaining wall and the top of the fixed retaining wall respectively; when 1.10≤B/H≤1.35

the slip surface is a curved surface

the starting point and the end point are the heel of the moving retaining wall and the top of the fixed retaining wall respectively; when B/H≤0.75

the slip surface is a "reflective broken line" composed of multiple straight lines

and the horizontal angle between the sliding line starting from the moving retaining wall and the fixed retaining wall is obviously different. In RT mode

the passive slip surface is a curved surface which passes through the H/4 point

the heel of the moving retaining wall and the top of the fixed retaining wall; in RB mode

the passive slip surface starts from the top of the fixed retaining wall and extends to the middle of the moving retaining wall

and the height of extension point gradually increases with the decrease of B/H.