Study On The Settlement Time Property Of Pile-slab Composite Foundation In Fengyang Section Of Beijing-Shanghai High-speed Railway

To improve transport efficiency and achieve separation of passenger and freight, construction of special passenger line and high-speed railway is imperative. Pile-slab composite foundation is a method commonly used to treat soft soil and incompact soft soil foundation of special passenger line and high-speed railway. But relevant design standards are not perfect, and specific guidance to the design and calculation methods is still scarce, and at the same time exploration of settlement time property and construction cycle after treated is not clear, which seriously impacts on its scientific nature.Based on above analysis, this paper, via construction background of Beijing-Shanghai high-speed railway, is intended to systematically study the settlement time properties of pile-slab composite foundation and analyze regularity and extent of parameter effect of pile-slab foundation on settlement time property, and the main factors are by settlement-controlled optimum design. The main research work and accomplishment of the paper are generalized as follows:Field tests of pile-slab composite foundation in Fengyang section of Beijing-Shanghai high-speed railway have been done, and field detection and observation results have been analyzed mainly including single pile and composite foundation and its deformation, load bearing of pile and soil, surface settlement, layered settlement, pore water pressure.Based on the penalty function contact of pile and soil, 3-D liquid-solid coupled numerical models of Biot consolidation theory have been established, and it has been verified that the models can better simulate settlement deformation of the field basic working conditions and are feasible in the study of settlement time properties through analyzing and comparing with field detection results.Through 3-D numerical model experiment, regularity and extent of parameter effect of cushion, pile length, pile diameter and pile space, initial void ratio, compressibility and permeability, filling height and filling rate under loading on excess pore water pressure of pile-slab composite foundation(bottom bearing pile and friction pile), pile-soil additional stress, surface settlement, deep settlement, compression of the reinforced area and compression of the underlying layer, is studied.Increasing pile length, pile diameter, initial void ratio of soil and permeability of soil and reducing cushion thickness, pile space and compressibility of soil, is advantageous to dissipation of excess pore water pressure and shortening the consolidation time and the effect of increasing permeability of soil is most remarkable. Increasing pile length and pile diameter and reducing cushion thickness, pile space, initial void ratio of soil and compressibility of soil, is helpful for controlling the settlement deformation and the effect of increasing pile length is most remarkable.The system of settlement-controlled optimum design of pile-slab composite foundation is established, and the main factors for pile-slab composite foundation of bottom bearing pile are pile space and surcharge preloading, and design ideas of sparse-density pile are brought; the main factors for settlement time property of pile-slab composite foundation of friction pile are pile length and surcharge preloading, and the ideas of settlement-controlled optimum design are brought.