Analysis and treatment for several engineering problems of foundation pits in Xining area

In order to solve the problems of land shortage and road traffic congestion, many cities in the northwest area of China begin to construct large-scale high-rise buildings and subways, which need excavate a lot of deep foundation pits. The application of the traditional supporting structures is restricted, while the pile-anchor supporting structures are widely used in deep and large scale founadation pits in northwest loess area owing to the advantages of initiativly improving the stress state of pit soils and limiting the horizontal displacement of pit sidewall. Based on deformation of typical foundation pits and collapse of several bracing projects in Xining area, such as the soil-nailing wall, composite soil-nailing wall, prestressed anchor, supporting pile, the existing problems in the design and construction are analyzed, and the corresponding solutions are proposed. At the same time, the lack of the current and similar excavation engineering in such aspects as design, construction and management is summarized, and the future researches should include: (1) establishment of soil pressure model based on displacement control of retaining structures in unsaturated areas, and improvement of soil pressure method; (2) strengthening of the field tests on retaining structures for deep and large foundation pits and establishment of dynamic stability model considering cooperative work of prestressed anchors, piles and soils. Finally, the common key quality control points are put forward in the construction of retaining structures.