Interactive behaviors of four closely spaced mega excavations in soft clays: Case study on an excavation group in Shanghai, China

One mega underground project that consisted of four closely spaced oversized excavations in Shanghai, China provided a rare chance to investigate the complex interactive behaviors of an excavation group in soft clays. Despite their much larger sizes and more complex unloading-loading conditions, lateral wall displacements, δh, of this excavation group were controlled within the half δh of local single excavations by implementing innovative construction procedures; however, the ground behind retaining walls underwent exceptionally large settlements, δv, as a result of superposition influence of neighboring excavations, which were 2.0–5.0 times those of local single excavations. Analyses of the extensive field data reveal that the interactive performance of an excavation group was governed largely by B (the width of a confined zone between two neighboring pits) and dfw (the furthest influence distance of Rankine failure wedge). If B>dfw, retaining wall of an excavation group behaved like those of single excavations in the case of either concurrent or sequential excavation of neighboring pits. If B