Deformation and failure mechanism of deep cement mixing walls: experimental study using physical model tests

This article presents the results of experimental research on the behaviour of deep cement mixing (DCM) walls during excavation up to failure. For this purpose, a novel laminar box equipped with a set of springs and a pneumatic loading system were designed and developed to run a total of nine scaled-down model tests at normal gravity on five different testing programs: (1) the wall thickness variation, (2) wall modulus variation, (3) effect of the reinforcement, (4) the bending stiffness (EI) control, and (5) the wall volume control of varying wall slenderness. The responses of the walls were studied through the wall horizontal displacement profile, tensile strains along with wall depth on the retained side, the distribution of strains using photogrammetric analysis and observation of crack initiation at the wall. The experimental results indicate that the behaviours of DCM walls depend strongly on the wall dimensions, particularly the thickness, and the analysis concepts used for conventional retaining walls cannot be directly utilized. The wall-to-excavation shape factor has been proven to effectively distinguish the behaviour mode and characterize the crack location concerning the wall height.