Abstract: The mechanical properties and design-calculation methods of pile-net composite foundation were analyzed, with the condition of pile’s end into and not into the hard soil layer. A mathematical model for the optimal design of pile-net composite foundation was established by taking pile diameter, pile length, pile cap length, pile cap thickness and pile spacing as design variables. The foundation bearing capacity, settlement, tensile strength of reinforced geotextile, bending capacity and shearing capacity of pile cap were constraint conditions, and engineering cost was the objective function to be optimized. By introducing the perturbation weighting and reducing parasitic operations, the perturbation-weighted symbiotic organisms search (PWSOS) algorithm was proposed to increase the convergence speed and accuracy of the symbiotic organisms search algorithm. Based on the perturbation-weighted symbiotic organisms search, the global optimization of the mathematical model of the pile-net composite foundation was carried out, and the optimal reinforcement scheme that meet the requirements was the output. The results show that the optimal design scheme has better economic benefit and the perturbation-weighted symbiotic organisms search algorithm has better performance.

Key words: composite foundation, optimized design, symbiotic organisms search algorithm, settlement, bearing capacity