Study On The Settlement Mechanisms And Method For Settlement Calculation Of Pile-Net Compound Structure On The Deep Layer Of Soft Soil Subgrade

For the embankment of high-speed railway,the requirement towards its post-construction settlement is as strict sa its stability,Interim Design Provisions for a New 200km/h Mixed Passenger and Freight Rai,Tentative specifications for design of new-built passenger railway with speed of 200～250 kilometers(first volume) prescribe and Provisional Design Specification for New 300-350 km·h^-1 Passenger Transit Railroad:post-construction settlement is less than 15cm and 10cm for Ballasted Rail in the speed of 200 km/h and 250 km/h,post-construction settlement is less than 5cm for Ballasted Rail when the speed is more than 300 km/h. Railway Design Guide of the Ballastless Track in Passenger Dedicated Lines prescribe:post-construction settlement is less than 15 mm for slab track.Settlement control demanding must be higher.The column-Net compound structure is a way dealing with deep layer of soft soil.The settlement is controled and Cost is saved for this way.The people pay attention to the way.The pile-net compound structure is used on the deep layer of soft soil subgrade, design is different in the building design.There is no standard to follow currently.Although foreign corresponding norms exist.But according to national norms calculated from the results vary greatly.It is necessary to analyze its applicability.The current domestic and international network for the pile composite structure of the mechanism are conducted research.But pile network structure of the composite pile cap and the impact of the mechanism is the lack of awareness.While pile net composite structure has not been the settlement calculation method that meet the mechanism.The foundation can only use the architectural foundation theory.So it is necessary to establish the composite pile-net settlement calculation method in keeping with the settlement rules and load transfer law to meet mechanism.Address oneself to the aforementioned problems,from the numerical simulation and field tests,theoretical analysis of the aspects of pile-net composite structure of the mechanism and settlement calculation methods it is studied and researched.The main contents of this study are as follows:(1)Though numerical analysis,the pile-net composite structure settlement rules and load transfer law is studied,the impact of pile spacing,pile cap on the settlement and load transfer is analysed.Combined with the typical the deep layer of soft soil condition,the impact of pile-net composite structure parameters for Pile-soil Stress Ratio of the deep layer of soft soil is analysed.(2)The field test of CFG pile-net composite structure is conducted.The settlement rule and load transfer law CFG pile-net composite structure is analysed. This Provide a basis for theoretical research.(3)Through practical engineering,compare with different national norms about stress calculation method on the Geogrid.The test proved that German norms is right and meet the need of calculation.On this basis,According to the characteristics of geogrid,simplify Geogrid for the membrane,deduce to membrane deflection equation on the elastic foundation.Further,deduce to Pile-soil Stress Ratio and pile efficacy calculation method Considering the role of geogrid.The impact of the pile spacing,filling height,geogrid tensile stiffness and rigidity of the foundation to Pile-soil load sharing Ratio is analysed.(4)According to the high-speed railway embankment design load,pile-net composite structure settlement calculation model is established.By assuming pile-soil interface friction with the relative displacement is the elasto-plastic relationship, relationship of pile side friction and the side pressure is linear,Pile-soil foundation model is Winkler foundation model,and combining soil-pile interaction mechanism,establish Synergies basic differential equations.Then piles and soil settlement analytical solutions of pile-net composite structure is get.Settlement analytical solution is verified through examples.(5)Throught the pile-net compound structure foundation settlement calculation methods and numerical calculation,it is analysised that the pile-net compound structure design parameters is on the impact of foundation settlement,and make appropriate recommendations.Finally,the direction about further research work is discussed briefly.