Some problems about retaining structures for shallow pits in deep and soft soil areas of Pearl River Delta

The soft soil of Pearl River Delta is the softest in China, which is characterized by high water content, high compressibility and low bearing capacity. In addition, it is of deep soil layer, low permeability, strong structure, rheology and preconsolidation. Those are likely to make the design and construction more difficulty, the project price higher and project accidents of foundation pits occur more frequently in this area. Especially when the excavation is 3~6 m (basement), some instability and local slip accidents are always induced because of the design, construction and management institutions' little attention. Aiming at the particularity of shallow pits in deep and soft soil areas and the problems found in engineering practices, some problems about retaining structures for the shallow pits in deep and soft soil areas are discussed: (1) common types and reasonable schemes; (2) modes of instability failures; (3) reasons of instability failures; (4) effects of passive zone improvement; (5) some project accidents about instability failures. This work may provide technical support for the design at shallow pits, and the relevant achievements may provide useful reference for optimizing the design and construction. It can be a good reference for similar projects.