Model Test And Pile Optimization Of Composite Foundation With Long-short-pile

Capacity of piles and soil bearing and control deformation will develop well in composite foundation with long-short-pile, it has wide application in losses foundation treatment in the provinces of the northwest, however, its theoretical research and load-bearing mechanism is lag relatively, which exert negative influence on its engineering design and practice, then hinder its sustainable development in the losses area.In this paper, analyzing calculation theory of multiple composite foundation, conducting six group indoor model test including soil、single pile、single pile composite foundation and composite foundation with long-short-pile, and performing numerical simulation of control uneven settlement by pile optimization in composite foundation with long-short-pile. Findings are as follows through above work:(1) On the basis of summary of composite modulus calculation theory in code,deduce a determination method of composite modulus and coefficient of bearing capacity of piles and soil of composite foundation with long-short-pile, and verify its rationality of the solution combined with model test.(2) In load test of Single pile, axial force gradually decreases from pile top to down, and changes trend of side friction resistance around pile is firstly enlarge then decreases from pile top to down; In load test of Single pile composite foundation, axial force gradually enlarge then decreases from pile top to down, the maximum axial force is 0.4 times length of pile under pile cap, side friction resistance around pile is turn negative to positive and gradually increase, which is the result of “shielding effect” by load-plate.(3) In the process of loading, change trend of pile and soil ratio is always increases rapidly, then gradually decreases after destroyed, which reflect that pile bear mainly load when load is small, soil bear mainly load when load is larger. So bearing capacity coefficient of pile should be developed completely, bearing capacity coefficient of soil will different along with load, but always less than 1.0.(4) In loading test of composite foundation with long-short-pile, long pile soil ratio is 1.35 times larger than short pile soil ratio, in which load is bear mainly by long pile; With the overlying load increases, both long and short pile soil ratio increases firstly then decreases, during the loading process, long pile soil stress ratio is always greater than the short pile soil stress ratio.(5) When composite foundation with long-short-pile laid down under raft foundation, tension stress and uneven foundation settlement can be controlled effectively by making adjustment to length of short pile distributed under middle and sides of the plate, meanwhile, it can save investment of the project.