Simpified Method For Deep Foundation Pit With Braced Retaining Structure

With foundation pits becoming deeper and deeper and their surrounding becoming more and more complex, how to guarantee the safety of foundation pits'excavation becomes the chief problem, and more accurate calculation method is the key. There are many primary methods for retaining structrure calculation, which both have their advantages and disadvantages. Therefore, exploring a kind of more accurate calculation method for retaining structures based on the advantages of primary methods is a valuable research field in academic and practical area.On the basis of the following practical conditions, this paper respectively establishs two species of simpified method (referred to as the first and second species of method in turn) for deep foundation pit with braced retaining structure: firstly, the axial line of inner support is below the axial line of top beam (middle beam); secondly, the two axial lines above are coplanar. The two species of method can reflect the interaction and retaining effects of the piles, top beam, middle beams and inner supports, whose researching object is one of retaining pile structural plane (separated from the four structural planes of deep foundation pit with braced retaining structure) and its corresponding top beam, middle beams and inner supports.1. This method roundly considers the interaction and retaining effects of the retaining structue, including bending and horizontal bracing effects of the piles; bending, horizontal bracing and torsional effects of the top and middle beams; bending and horizontal bracing effects of the inner supports.2. Compared with Spatial Finite Element Method, this method not only can reflect the spatial effects of deep foundation pit's retaining system, but also is simple and convenient. Compared with m-method, this method not only can consider the interaction of the piles, top beam, middle beams and inner supports, but also treats the interaction between the piles and inner supports according with the practice more perfectly. 3. This method can conveniently provide the dynamic simulations for construction processes of excavation, middle beams and inner suports, and can consider the influence the last construction stage acted on the next stage.4. For every excavation stage, this method can calculate any section internal forces and displacements of the retaining structue, which can provide the basic data for the design and reinforcement of the retaining structue and evaluation for the influence the foundation pit's excavation acted on the surrounding.5. Not considering the influence of the position differences between the axial lines of top beam (middle beam) and inner supports, the calculation results of the two species of method only have the differences for the force and torque values piles acted on top beam (middle beam) at the position of inner supports. But there is a simple conversion relation for the differences. In addition, the first species of method is more simple than the second.Spatial Finite Element Method of Bar System is another calculation method which can roundly consider the retaining effects of the retaining structue and has been checked by the engineering practice. This paper calculates the retaining structures of an engineering example using both simplified method for deep foundation pit with braced retaining structure and Spatial Finite Element Method of Bar System. By comparing the calculation results and the monitoring results, the accuracy and rationality of simplified method for deep foundation pit with braced retaining structure are validated.Retaining structure of deep foundation pit composed of retaining piles, top beam, middle beams and inner supports is a organic system. Every component part has its own supporting effects, and every supporting effect makes different contribution to the retaining system. Through comparing the calculation results for the retaining structure of the deep foundation pit engineering example by using both simplified method and its correlative methods, this paper gets some useful conclusions about the interrelation among the component parts and the contributions of different component parts to the retaining system.The corresponding Fortran programs are designed for the simplified method and its correlative methods.