Limit Analysis On Ultimate Bearing Capacity Of Soils Under Caps Of Composite Pile Foundations

Composite pile foundation is a kind of foundation form considering pile-soil interaction and making full use of bearing capacity of soils around piles. It is important to definite ultimate state and bearing capacity of soils under strip caps with circular or rectangle piles. So through upper bound theorem of limit analysis this paper researches into them with surface caps and weightless soils, or with all considerations. This will help improve composite pile foundation theory and promote its application. Comparing with existing examples and model test results, the main research concludes are just as follows:(1) Horizontal failure mechanisms and velocity fields of soils around circular and rectangle piles in the limit state being established, formulas of ultimate bearing capacity increment of barrier effect under strip caps are deduced. Calculation results show the increment works considerably in soft cohesive soils, and rectangle piles strengthen soils more than circular ones. So square pipe pile is a perfect section form for composite pile foundation and anti-sliding pile designs.(2) When piles are at the edge of caps or the distance between them is small, calculate ultimate bearing capacity of soils ignoring effects of pile position. It will simplify the course and get close results, especially in soft cohesive soils.(3) The soil in depth of embedment can restrain foundation deformation and improve its ultimate bearing capacity. Annex or other load around main building sides can also do. They may be well used in the design with the notice of load scope.(4) Comparing with Vesic formula and examples, formulas of ultimate bearing capacity of soils under strip caps are validated reasonably and feasibly based on limit analysis in this paper. The status and sensitivity of bearing capacity makeup parameters being analyzed, it concludes that corresponding design schemes and their values should be adopted carefully according to different engineering conditions. At the same time, disadvantaged effects of natural conditions also need attention.(5) Comparing with model test results, it shows feasible that the failure mode of soils under caps is simplified as Prandtl mechanism in plane problems of composite...