The Engineering Characteristics And Numerical Analysis Of Composite Foundation With Different Reinforcement

With the increasement of the high-rise buildings and irregular buildings, the differential settlement of natural foundation is becoming more and more strict, especially the soil which is under the foundation is complex and specific, such as liquefiable soil, filling and collapsible loess. Because these natural soils can not meet the requirements of bearing capacity and deformation, it must be reinforced. Composite foundation with different reinforcement has significant advantages in controlling differential settlement, and has got very good application in many engineering examples. This paper introduces the basic concept, design principles and engineering characteristics of composite foundation with different reinforcement simply, summarizes and analyses the advantages and disadvantages of the current calculation methods of bearing capacity and settlement deformation.Secondly, this paper analyses the settlement deformation of composite foundation with different reinforcement based on a project. Due to the natural foundation of this project can not meet the requirements of bearing capacity and deformation, and there is thick filling which is based on fly ash under the foundation. So two different treatment schemes is put forward, in order to make full use of the fly ash and improve the bearing capacity, we decide to adopt cement deep mixed columns to deal with the filling layer. At the same time, using CFG pile to deal with the deep soil can meet the needs of the deformation. According to this scheme, using the finite element software PLAXIS 3D to build two models to compare and analyze the settlement, model 1: composite layer model, model 2: pile unit model, the final simulation results are compared with the measurement data of settlement and the result which is simulated by FLAC 3D, there are some conclusions :(1) Composite foundation with different reinforcement include the pile, the soil between piles and cushion. Because of the negative friction, the maximum axial force of the pile will appear in the neutral point, and the neutral point and Pile-soil stress ratio will change with the increasement of the load. In the whole process, according to the principle of stiffness distribution, we can know that the main pile bear the most of the load, the soil among the piles can bear a little.(2) For the foundation treatment of complex engineering, some factors must be considered, such as bearing capacity, differential settlement. For this project, the CFG pile is mainly used to control settlement and the cement deep mixed columns is used to improve the bearing capacity of the filling layer.(3) From the simulation results, we can know that model 2 is better. The biggest settlement appeared in the middle of composite layer model and the surrounding settlement is smaller, and it can not comply with the design requirements. Similarly, we can know that the biggest settlement of pile unit model appeared in the middle of the foundation and the edge of the foundation, all of the settlements can meet the design requirements.(4) The results of the pile unit model were compared with the measurement data of settlement, we can know that the deformation trend is very consistent, the biggest settlement appeared in the middle of the foundation and the edge of the foundation. Therefore establishing model of interaction between each unit intensively can approach the real situation preferably.(5) Further simulation with FLAC 3D verifies the responsibility of the result of PLAXIS 3D and the reasonability of composite foundation with different reinforcement. At the same time, comparing the two softwares in calculation principle and operability, we can provide some guiding significance for the future numerical analysis.(6) Because different piles reinforce different depths of the foundation, The detection scheme is more complex. This engineering adopt Vertical Static Load Test on Single Plie, Law strain reflected wave testing and Load Test on Composite Foundation to comprehensive evaluate the quality and the bearing capacity of the pile foundation, and all indexes can meet the design requirements.