The Research On The Optimization Design Of CFG Piles Composite Foundation Based On MATLAB

Cement Fly-ash Gravel (CFG) pile composite foundation is a kind of vertical reinforcement composite foundations. As industrial waste fly-ash can be added and no steel is needed in this method, as well as the bearing capacity of soil can be fully used, engineering cost of the CFG piles normally is only 1/3 to 1/2 of that for pile foundations. Due to remarkable economic and social benefits, CFG pile composite foundations are applied into engineering practice more and more widely. In general design each parameter is primarily assumed a value according to the required bearing capacity, and then it is adjusted to satisfy the settlement limitation of subsoils. It may take many trials in the calculation, while the result still may not be economical. Thus it becomes very urgent to look for a more reasonable design method.Firstly, the basic theory of composite foundation is introduced, including the calculation methods about the bearing capacity and settlement of the composite foundation, then the requirements of the design calculation by standardization about CFG piles composite foundation are introduced. Secondly, following the theoretical preparation of CFG piles composite foundation is the optimization design theory. Emphasis is paid on three key elements of the optimization problem model, including design parameters, objective function and constraint conditions, and then is the flow chart of the optimization design. Thirdly, this paper briefly covers the basic knowledge of MATLAB software, and a specific introduction to the flow control statements of MATLAB software is shown.The influence of design parameters which include pile diameter, pile length, area replacement rate and strength of the CFG piles on stabilization effect is analyzed. Through an established homogeneous soil mass model of 60m thick, the relationships between design parameters and bearing capacity and settlement of CFG pile composite foundation are shown by using the graphics of MATLAB. This work provides basis to select the design parameters for the optimization design of CFG piles composite foundation.According to above-mentioned theoretical preparation, the author adopts the pile diameter, pile length, and area replacement rate as the main design parameters, while considering the strength of the piles. The permitted bearing capacity of composite foundation and total controlling settlement are taken as the constraint conditions, and the total volume of the CFG piles mixture is selected as the objective function. The design achieving the least amount of the CFG piles mixture is the optimum one. Using MATLAB as a computing platform, the author sets up a flow chart of the optimization design according to the features of MATLAB's flow control statements.In the paper, a practical engineering project is taken as an example to carry out optimization analysis. With the same settlement value in original design, it shows the volume of CFG piles mixture in the case can be saved up to 10%.