(1. Guangdong Research Institute of Water Resources and Hydropower，Guangzhou，Guangdong 510610，China；2. The Geotechnical Engineering Technology Center of Guangdong Province，Guangzhou，Guangdong 510610，China；3. School of Civil and Architectural Engineering，Wuhan University，Wuhan，Hubei 430072，China；4. Pearl River Hydraulic Research Institute，Guangzhou，Guangdong 510611，China)
Abstract：The soft soil in the Pearl River Delta area has the features of high water content，high compressibility and low carrying capacity，etc.，which has put forward more stricter requirements for the design and construction of foundation pit project. Therefore，the supporting design under complicated environment for deep foundation pit on soft soil has become a new topic for geotechnical engineering. According to the particularities of the soft soil foundation pit，four key problems during the foundation design of soft soil foundation pit are discussed：(1) The force and deformation processes of the supporting structure are analyzed by the incremental method. (2) When considering the impact of the prestresses of the pit anchoring bolts and anchoring cables，the prestress leads the soil on the positive side of the foundation to suffer pressure. Therefore，the soil mass at the positive side shall be equivalent to earth spring. As for whether the earth spring has participated in the impact shall be judged by the displacement of the earth spring. (3) When the soft and weak earth foundation existing during the slope cutting，it is not only need to verify the overall stability of the foundation pit，but also need to verify the stability and carrying capacity of the earth foundation. (4) There are many issues about the forcing and deformation of double-row piles supporting structure needing to be studied further. With the specific engineering，the simplified calculation method of double-row piles is proposed. Many soft foundation engineering accidents have also illuminated that the foundation will have potential hazard risk if the above four key problems have not been thoroughly considered. Finally，based on the design of soft soil deep foundation pit，taking the solving method of the above four key problems as the theoretical support，the rationality is verified；and the common design scheme for adopting multi-supporting techniques for soft soil deep foundation pits are analyzed in detail，so as to provide some guidances for other similar projects.
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2012, Vol. 31 
