Study On Interaction Characteristics Of Subgrade-Composite Foundation-L Retaining Structure Of Passenger Dedicated Line

With the development of railway construction,the problems of land resources shortage,tight construction period and uneven settlement of subgrade are more and more prominent.The normal slope embankment not only occupies a large amount of cultivated land,but also the natural soil subgrade or common subgrade treatments cannot meet the post-construction settlement requirements of high-speed railway and passenger dedicated line.Therefore,a large area of foundation treatment is needed to control the post-construction settlement and structural deformations.Thus,there is a great application space and development prospect for the new type of subgrade composite foundation-L retaining wall structure.(1)composite foundation and structure stiffness match,(2)Influence of subgrade settlement on distribution of soil pressure on retaining structrure(3)influence of soil pressure change on uneven settlement.This article is studied subgrade composite foundation-L retaining wall by means of above following several factors.By optimizing the combination of the retaining structure and foundation stiffness.It is better to apply this kind of complex structure system to normal railway construction.The main conclusions are as follows:(1)The change of foundation and retaining wall stiffness has a significant influence on overturning direction of retaining wall and uneven settlement of subgrade.Under the condition of unchanged subgrade material,uneven settlement of asymmetric structure can be effectively controlled by changing foundation and retaining wall stiffness.With the foundation stiffness increasing,the overall settlement decreases,and the uneven settlement also decreases.When the foundation stiffness reaches 500 MPa,the foundation settlement tends to be stable,When the stiffness of the foundation is small,the bearing capacity and deformation of the foundation cannot meet the requirements of the asymmetric structure subgrade.at this point,manual processing is required.When the foundation condition is good,with the increase of retaining wall stiffness,the anti-deflection deformation ability of the structure increases,the side settlement of retaining wall decreases obviously,Meanwhile,the overall settlement decreases,the retaining wall stiffness plays a significant role in controlling the uneven settlement of the structure,but the retaining wall stiffness is not larger is better.There is an optimal thickness value that is reasonably matched with the foundation stiffness.Or different thickness of retaining wall can control the deformation of cantilever retaining wall,at the same time,there is an optimal stiffness which can control the overall settlement and the uneven settlement of subgrade.(2)The structure soil pressure distribution is not a triangula described by the classical earth pressure theory,but a parabola that gradually increases along the top to the bottom of the wall and then decreases under the constraint of the retaining floor.The filling modulus,CFG pile length and pile diameter have little influence on the earth pressure,and the retaining wall stiffness has the greatest influence on the earth pressure.The retaining wall stiffness(thickness),pile spacing and filling parameters(include angle of internal friction,cohesive force and filling modulus)have great influence on the uneven settlement of subgrade,and the length and diameter of CFG piles have little influence on the uneven settlement.As the angle of internal friction of the filling increases,the earth pressure decreases.When C>15kpa,the earth pressure basically does not change.Because of subgrade is prone to instability and failure when the angle of internal friction of thefilling is less than 10 degrees,it is suggested that the angle of internal friction of the fillingl should not be less than 10 degrees in practical engineering.when the pile diameter is larger than 0.5m,the subgrade settlement is basically stable.It is suggested that the pile diameter of CFG pile for practical on-site construction is 0.4-0.5meters.Considering the control of the displacement and deformation in the transverse direction,it is suggested that the pile spacing should be 1.4-1.8 meters in practical engineering.(3)The foundation stiffness required by different retaining wall stiffness(thickness)to meet the settlement requirements of high-speed railway subgrade design specification is obtained through finite element calculation and analysis,and the variation rule of foundation stiffness with the change of retaining wall thickness to meet the settlement requirements of the specification is summarized.The variation rule is that within a certain range,as the retaining wall thickness(stiffness)increases,the foundation stiffness required for uneven settlement of 2mm gradually increases,and the foundation treatment stiffness required for settlement after construction gradually decreases.