Shanghai-Nanjing Intercity Railway Pile - Net Composite Foundation Deformation Characteristics And Settlement Calculation Study

To deal with the deep layers of soft clay ground,comparing with traditional composite foundation of CFG piles,the CFG pile-net composite foundation can strengthen the natural ground from two directions:vertically and horizontally,which makes more complex to analyze its deformation and sedimentation. The background of this paper is the science and technology project initiated by the Ministry of Railway—"The construction safety and subsidence monitoring technology of Shanghai-nanjing inter-city railway (Numbers:2009G008)".Based on the test of Shanghai-nanjing inter-city railway foundation in Zhenjiang section on site, the paper analysised and summarized the data of foundation settlement,geogrid deformation and the lateral displacement, studied the deformation characteristics and settlement calculation of pile-net composite foundation.So the main work and conclusions are as follows:(1)The pile-net composite foundation is a new treatment to high-speed railway soft subgrade.According to the geological conditions and design scheme,this paper selected three sections of Shanghai-nanjing inter-city railway for test on site,and buried some instruments like displacement meters,settlement meters and level displacement pipes,etc. The monitoring data is obtained.(2) According to the field test,the paper obtained the behaviour of the settlement and deformation for pile-net composite foundation soil:Soil arching effect was the important factor that affect the deformation of geogrid net effect;There were certain pressure area located in arch feet and the middle of arch;The main settlement of foundation soil occurred in the reinforced procession (67% to 87%);The results showed that the collaborative work offered by piles and soil produced good effect to the soft subgrade through the adjustment of the reinforced cushion.(3)By considering the pile and nets'related parameters, this paper derived a calculation formula which can calculate the instant settlement of soft ground improved by sand piles in the bank load of the high-speed railway, and verified its precision. (4)Based on the measured settlement process curve, this paper established a new settlement prediction model by taking in the thoughts of variational coefficient.Comparing with the model recommend by standards, the results showed it is unique,higher precision and more practical.