The Analysis On Supporting Structure Project Selection Of Deep Excavation In Loess Region

Under the safe and dependable premise, it is an important task to select rational supporting structure of foundation excavations, optimize the structure, lower the consumption, save the cost, realized the best combine of economy and technology. At present, the calculation and design of supporting structure of deep foundation excavations is quite complex, and the project selection is normally not suitable also. Aimed at the problems above, structural optimization and project selection in loess is studied in this paper.According to the geotechnical characters of loess in northwest of China and many design experiences for practical project, several supporting structures, such as the structure of pile-prestressed anchor, the structure of frame retaining wall with prestressed anchor and the soil nailing wall, are suitable for foundation excavations in loess. According to Technical Specification for Retaining and Protection of Building Foundation Excavations—JGJ120-99, the design methods of suitable structures are summarized and generalized, and the calculation theory and model are improved as follows: First, a finite element calculation model of the pile-prestressed anchor supporting structure is proposed, which assumes that the pre-stressed anchors serves as the elastic supports of the pile body, and the solution method to the model equation, which is hyper static, stress-strain coupling is put forward. Second, the dynamic relationship between the location of the slip surface, the nail length and diameter is incorporates. And to emulate the foundation excavation stage stability is suggested to be analyzed by step.Based on the theory analysis above, the optimization models of the pile-prestressed anchor supporting structure, the frame supporting wall with prestressed anchor structure and the soil nail wall is created. These optimization problem are solved by Genetic Algorithm, which emulates the evolution of creature in nature, and the corresponding solving program is worked out by the language of Matlab.At last, through the economical efficiency comparison and analysis of three kinds of supporting structure while geotechnical characters of loess and slope heights are different, the characteristics and rules of supporting structure are concluded, also a project selection method and corresponding select process chart are proposed, which are approved to be suitable and feasible by practical case. The method of analysis, calculation and study in this paper can also be applicated in the project selection study in other area.