Analysis And Countermeasure Research Of Geosynthetics Reinforced And Pile Supported Structure Settlement Of High-speed Railway Subgrade In Soft Soil

Settlement deformation is the main problem for high-speed railway subgrade,and the foundation is the main source of settlement deformation,especially in deep soft soil area.Pile-net composite foundation is one of the main foundation treatment methods of high-speed railway in china.The source of settlement of pile-net composite foundation is various,including the compression of pile cushion,the compression settlement of reinforced zone,the compression of substratum and the penetration deformation of both pile top and pile bottom.In pile-net composite foundation system,many studies has been done on settlement and deformation of reinforcement zone.There is a lack of reliable analysis and calculation methods for the both pile top and bottom penetration deformation,the inherent law of the overall settlement needs to be studied.Moreover,the demand for fine calculation and high precision control is still required for high-speed railway.In this paper,the settlement analysis and countermeasures of pile foundation composite foundation system of soft soil road of high-speed railway are studied.Through the simulation calculation and model test of single pile,the deformation and failure mechanism of cushion reinforcement of pile-net composite foundation and the law of deformation of cushion under different conditions are studied.Through the model test,the load transfer and deformation characteristics of pile-net composite foundation are studied.The load distribution characteristics of pile top and bottom plane and the deformation law of pile top and bottom penetration are analyzed.Through field test,the bearing capacity of rigid pile and the distribution law of side friction resistance of pile are analyzed,and the calculation model and method of pile-net composite foundation settlement are studied systematically.In view of the settlement deformation of pile-net composite foundation,the corresponding countermeasures are analyzed and studied.The main results are as follows:(1)Reveals the interaction characteristics and deformation rules of reinforced cushion and pile end.The complete deformation form of the cushion reinforcement at the top of the pile and between the piles is obtained,the location of the maximum strain of reinforced is different from the theory of suspension between piles.The correction of the existing reinforcement tension calculation is revised,and the formula for design and calculation of reinforced cushion is proposed.(2)The settlement and deformation characteristics of pile-net composite foundation are obtained.Based on the test of membrane pressure distribution sensor,the continuous pressure distribution at the interface between the pile head and the cushion,and the pile bottom and the substratum is verified.A simplified calculate formula for the deformation of pile top and bottom penetration is presented.(3)Based on the stress distribution at the bottom of the pile,the influence depth of the local concentration stress of the substratum under the pile bottom is obtained.A scheme for calculating the local stress concentration zone and the stress distribution area in the substratum settlement is put forward.Considering the effect of cushion,the existing soil arch structure is optimized.(4)A calculation model of composite settlement system for pile-net composite foundation of high-speed railway is established,the effectiveness of the model is verified by model tests and field tests.Based on the settlement characteristics of pile-net composite foundation of high-speed railway,the improvement measures for settlement of different parts are put forward.