Passenger Green Pile - Net Composite Foundation Field Test And Numerical Analysis

The pile-net composite foundation is a type of ground treatment which bearing the load by making pile-net-soil working together, and has been used widely in recently years. This method is used in the high-speed railway (high way) foudation treatment, bumping at bridge-head treatment, oil tank foundation and structural engineering and so on. According to the existing project examples, this method has remarkable effect on soft foundation treatment. There are several advantages for pile-net composite foundation, such as rapid construction speed, small disturbance to surrounding environment, small heterogeneous settlement for post-construction, and the most of settlement occur in construction period, etc.Because the pile-net composite foundation is used in the subgrade engineering of the high-speed railway, the design is different from the building engineering. Therefore, there is no existing standard to apply currently. Although there are corresponding criterions in foreign countries, the calculating results which based on these standards have obvious difference. For this reason it is necessary to analyze its applicability.Based on the previous research results, this paper investigated and discussed the working characteristics of the pile-net composite foundation by theoretical analysis, field tests and numerical simulation. The main conclusions as follows:(1) The load of soil above the reinforced cushion was calculated by applying German criterion, and the form of subsidence for reinforced cushion was simulated by quadratic parabola, the formula of pile-soil stress ratio was derived. The impact of the filling height and internal friction angle of filling, radius of pile, interval of pile and pile earth differential settlement to pile-soil stress ratio was analysed.(2) The monitoring datas is obtained by burying instruments on site. The bearing mechanism and load transfer mechanism of pile-net composite foundation were obtained by monitoring the datas of base stress, pile-soil stress ratio in different position and the strain of geotechnical grille in reinforced cushion. Based on the observation datas which considering the deformation of the pile and soil, horizontal displacement of foundation, and the variation pore pressure, the settlement and deformation rule of pile-net composite foundation is obtained.(3) Combining with practical project, the working characteristics of pile-net composite foundation was investigated using finite-difference code FLAC and the influence law of settlement and horizontal displacement for pile-net composite foundation, axial stress of pile, force of geogrid and pile-soil stress ratio caused by the factors of pile length, pile diameter and pile spacing was analyzed.(4) According to the settlement forecast which based on the field measured data and the definition and formular of post-construction settlement, the post-construction settlement of corss section for settlement forecast was predicted. The calculating results shown that the valus completely meet the requirement of post-construction settlement for passenger dedicated line.