Research On Bearing Capacity Behavior And Optimization Design Approach Of Reticulate Root Pile

Root pile, also known as micro-pile. Since the 1950s, it has been used from strengthening and underpinning original foundation of the old building to slope stability, shoring deep foundation pit,and so on. The deformational behaviors are different between the reticular root pile foundation and the single root pile. It is further difficult in its working behaviors due to the interaction among the pile-soil-upper structure. Presently, we don't know thoroughly the interactional characters between the pile and soil under the load. Many designs are still based on practices. A systemic method of design is not formed. Solving these problems will open up the development root piles even broader application prospects.According to the needs of engineering practice, the research status and the achievements of root pile, this paper firstly analyze the load transfer behavior of the single root pile under the vertical load. In accordance to the load transfer function analytic method by Sato Satoru, the critical pile length calculation of the single root pile is concluded under the vertical load in the homogenous soil.Then we study the load transfer laws and the deformational characters of the single root pile under the vertical load by numerical analysis and discuss some influence factors in its bearing capacity and deformation, such as length, diameter, the concrete degree of the pile, as well as the elastic module of the pile-side soil and the pile-end soil. Based on deformational comparative analysis between the single pile with cap or not, we go on study the working behaviors of the reticular root pile group under the load. Its finite element model is built by adapting the three dimension finite element program. After studying detailedly on its stress and settlement characteristics under the vertical load, we analyze the influences in foundation settlement result from the adjacent pile spacing, pile length and the numbers of pile. By discussing the settlement characters of pile group foundation with the variation range of spacing between adjacent piles in 2-7times root pile diameter, the optimal pile-spacing range,efficiency factor of pile group and settlement ratio are obtained, as well as critical length of pile in the group under the optimal pile-spacing. Finally, based on the view of system, we built a multi-dimension optimal design model, where the geotechnical design principles and pile-soil interaction research results as a part of it, the lowest cost match the constraint conditions of various designs, specifications, construction conditions etc. as the goal function. It can be solved by using mathematical programming optimization methods, and made the final decision by combining with the engineering experience.In this paper, by using theoretical and numerical methods, we thoroughly study in the working behavior of root piles under vertical load and get some conclusions. These conclusions can give certain references in choosing length, spacing, numbers and concrete degree of root piles. The optimal design model can make the optimization avoid the "pure mathematic", and they have some applied values.