Force Chain Effect of Deep Foundation Pit Supported by Soldier Piles in the Sand-Gravel Layer

Soldier pile support is an important tool for supporting deep foundation pits in the sand-gravel layer. However, since the sand-gravel layer itself is an aggregate of particles, its noncontinuity will cause extremely complex changes in the properties of the surrounding soils during pile supporting, and the changes in the mechanical properties of the soil behind the piles can also affect the safety and stability of the pit. To study the changing pattern of the surrounding soil in the course of pile supporting, we used the numerical method to simulate an excavation in the sand-gravel layer, followed by an analysis of the movement and stress distribution of the surrounding rocks. A photoelastic experiment was carried out to simulate the excavation process and study the force chain network of the surrounding soil as well as its changing characteristics. As shown by the results, (1) during the excavation of a deep foundation pit supported by soldier piles, on the same horizontal plane, the force chain changed most dramatically at the position that was 13.8 m (depth of the foundation pit) away from the edge of the foundation pit; (2) during the excavation, the force chain structure of the surrounding soil changed from vertical development to both vertical and horizontal developments; when there was a hard rock layer at the bottom of the soldier piles, the supporting effect of the piles was mainly provided by the hard rock layer; (3) the free face should be reinforced, and the excavation face should be adjusted based on the underground conditions of surrounding buildings (structures).