Experimental study on mechanical response of new type composite envelopment of deep foundation pit in composite formation

Abstract With the continuous development and construction of the city, the excavation depth of the foundation pit is gradually increasing, and the retaining structure is facing difficulties in rock entry and poor economic benefits. Therefore, a combined retaining structure of the foundation pit with the upper part of the underground diaphragm wall and the lower part of the bored cast-in-place pile is proposed. In-depth research on the mechanical properties and supporting mechanisms of the structure is still lacking. Therefore, this paper conducted a similar indoor model test. The results show that after the foundation pit excavation, the surface settlement is triangular. The horizontal displacement of the structure is “internal convex”, and the deformation mainly occurs in the upper soil layer. The peak of the bending moment on both sides of the structure mainly appears near the soil-rock interface and the pile-wall interface. It is found that the moving down of the pile wall interface can well reduce the peak moment and the relative moment difference. On the premise of ensuring the safety of the foundation pit and taking into account its economy, the upper wall of the new combined foundation pit enclosure structure is recommended to be at least 5 m into the rock.