LAUSR

Excavation types of foundation pits for large-scale or special-purpose urban construction have been more and more complex, and the environmental safety issues caused by pit excavations are unprecedentedly significant. This paper presents an interpretation of the lateral response of group piles to a peculiar pit-in-pit excavation where the inner foundation pit located in the center of the outer pit is continued to excavate after the completion of the outer pit excavation. The support system of the pit-in-pit excavation is provided by diaphragm walls and multiple levels of rigid bracing. The numerically horizontal displacement of the diaphragm wall and the surface settlement of the outer pit caused by inner pit excavation were examined and compared with theoretical models. The cumulative influence of the pit-in-pit excavation system on the lateral bearing mechanism of existing piles in the transition zone and the additional impact characteristics of the piles induced by inner pit excavation were analyzed. A parametric study was subsequently conducted to investigate the effects of the inner pit geometry (plane area and excavation depth) on the lateral pile performance. Results revealed that the mechanism of lateral piles in the transition zone is attributed to the coupling effect of the inner and outer pit excavations. Moreover, the excavation area of the inner pit plays the significant influence compared to inner pit excavation depth. Finally, a loss ratio (δ) method to practically evaluate the degree of loss of lateral bearing capacity of the piles at different locations of the transition zone due to pit-in-pit excavation was proposed.