| dc.description.abstract | This thesis presents the application of optimal algorithms to the least cost design of bored piled foundations. The objective function is the combined costs of soil excavation, pile cap, piles, and soil backfill. The design variables, including pile length, pile diameter, depth of pile cap, pile spacing, and pile number, are all discrete. The optimal algorithms include discrete Lagrangian method (DLM), modified relative difference quotient algorithm (MRDQA), real-coded genetic algorithm (RGA), and hybrid genetic algorithm (HGA). The efficiency and validity of the above algorithms have been verified by comparing the solutions with the global optimum solutions obtained from exhaustive search method (ESM).
The comparative results of seven design cases have shown that the mean errors of DLM and MRDQA solutions are around 1.86%, respectively. RGA and HGA can find the optimum solutions from ESM, but they spend more time than DLM or MRDQA. The influences of the unit price of the constructive materials, soil liquefaction, the resistance of pile cap, and the pile-group effect on the optimum solutions are discussed in the thesis.
Furthermore, the thesis presents a simplified nonlinear pushover analysis for the lateral response of the pile subjected to liquefaction-induced flow earth pressure. The pushover analysis can be carried out by incrementally imposing flow pressure or flow displacement on the pile. The capacity curve of the lateral pile was expressed in terms of the total flow forces and the displacement of pile top. The seismic performances corresponding to different liquefaction extents can be clearly identified on the curve. The field damage case was analyzed by both of the flow pressure and displacement methods. A comparison was made between the results of these two methods. It shows that both two
methods can reasonably capture the lateral pile response when subjected the flow pressure due to ground liquefaction. However, the flow pressure method seems more suitable to be used in the area of seismic performance-based design of pile foundation.
Although pushover analysis can capture the pile response very well, it is so complicated that the analyses usually have to be solved by numerical methods. Based on some reasonable assumptions, the thesis presents a simplified closed-form solution for the analysis. It is a combination of the solutions of an Euler’s beam and an elastic lateral pile. The solution is used to analyze two cases of damaged pile due to lateral spreading. The calculated result by the solution agrees the field performance well. Based on the simplified closed-form solution, the influences of pile diameter, pile spacing, peak ground acceleration, the SPT-N value of liquefying layer, and the SPT-N value of non-liquefying layer on the lateral pile responses are discussed in the thesis. | en_US |