Study On Settlement Properties Of Pile-Slab Composite Foundation In Beijing-Tianjin Special Passenger Line Subgrade

In construction of Special Passenger Line in soft foundation,it is imperative to solve the key problem of subgrade settlement.Transplanted from civil engineering, pile-slab foundation works as a new effective means of foundation treatment.It bears so many advantages including:quick and short construction process,high bearing capacity and rigidness,good stability and durability,proper cost,uncomplicated construction techniques,and significant environmental safeguard.However,due to its complicated working mechanism,research work is by now somewhat lagging in that no theoretical system has been established to fulfill the calculation and exploration of settlement property,and no relevant design standards have been set.Moreover,the engineering practice has still been in the trial-and -error and experience accumulation procedure. Normal composite foundation theory and design experiences are mainly applied,thus hindering the scientific application of pile-slab foundation means.Based on above analysis,this dissertation,via construction background of Beijing-Tianjin Special Passage Line,is intended to first systematically study the settlement properties of pile-slab foundation under dead and dynamic load and analyze regularity and extent of parameter effect of pile-slab foundation on foundation settlement.The methods of theoretical analysis,site experiment,numerical simulation etc.have been applied.The main research work and accomplishment of this dissertation are generalized as follows.Site tests o f pile-slab foundation in Beijing-Tianjin Special Passage Line have been done,and site observation results have been analyzed including static load test of pile,integrity testing,deformation properties of ground settlement,lateral displacement property of ground,settlement regularity of pore water pressure,and pile-soil stress property.3-D finite element model of pile-slab foundation is established to analyze the settlement properties of pile-slab foundation and varying pattern of additional stress.At the same time,some parameters,affecting the mechanic properties of pile-slab composite foundation are studied involving pile modulus,pile length,pile space, subgrade height,cushion thickness and its modulus,reinforced concrete slab modulus and its thickness.The results are of constructive significance to the design and application of pile-slab foundation. From the viewpoint of system,coupled dynamic analysis model of vehicle-track was developed and vehicle/track coupled dynamic equation were derived based on the D'Alembert principle and solved.Curves of time history of dynamic load of vehicle was gained.Plain strain model of pile-slab composite foundation is developed to analyze the dynamic response law of calculation model under the high-speed train dynamic load.The law of motion speed and some relevant parameters affecting dynamic index of the pile-slab composite foundation has been further explored.Based on the calculated analysis on settlement property of pile-slab foundation under static and dynamic load in chapterâ…£andâ…¤,the design method of controlling pile-slab foundation settlement is discussed.It is feasible and practicable to regard the pile length and pile space as structure design parameters,settlement or settlement of subgrade after acceptance as constraint variables,and engineering cost as goal function to make a settlement control structure design of pile-slab composite foundation.