Research On Post-construction Settlement And Treatment Of Bridge-Approach Of Expressway Pipe Pile In West Dongting Lake District

The soft soil in the West Dongting Lake area is widely distributed,and the mechanical properties of the soil are poor.In the transition section of bridge approach on soft soil foundation,differential settlement is often caused by the stiffness difference between the abutment structure and the embankment on the back of abutment.At the same time,large post-construction settlement is caused by inadequate foundation treatment,and then it will affect the smoothness of the line in the transition section.To solve this problem,relying on the expressway project in West Dongting Lake area,this paper treated the soft foundation of bridge head with the same treatment method and different treatment schemes,and analyzes the post-construction settlement and transition smoothness of the subgrade top under different transition schemes,and obtains the appropriate transition scheme,so as to provide reference for the subsequent construction of expressway in West Dongting Lake area.The main research contents and results include the following points:(1)By analyzing the field monitoring data,it is obtained the regular that with the increase of filling load,the overall settlement curve presents a "basin" shape trend,and the horizontal displacement curve of foundation presents a "bow" shape.The post-construction settlement is predicted by hyperbolic method,which paves the way for verifying the effectiveness of model calculation later.(2)The three-dimensional model of the bridge transition section is established by using ABAQUS finite element software.It is obtained the regular that transverse and longitudinal of itD,horizontal displacement of foundation abutment displacement force law.In the transverse direction,the settlement of roadbed shows a small law on both sides,and the settlement of foundation increases with the increase of the distance from the platform back.In the longitudinal direction,the settlement of foundation and subgrade reaches the maximum at the center line;and the maximum horizontal displacement of foundation appears 6.8m below the foot of slope;and the abutment body is offset to the front,the front pile is subjected to a greater push forch than the back pile,and the horizontal stress ang displacement reach the maximum at the bottom of the cap.(3)Based on the differential settlement control standards at home and abroad,combined with the engineering practice,the ride comfort evaluation index of the transition section in this paper is proposed:allowed post-work settlement、allowable longitudinal、slope difference and the radius of transition zone curve.By analyzing the change trend of post-construction settlement of the subgrade top surface and evaluating according to the smoothness evaluation index and analysis the structural stability,thus determine the appropriate transitional treatment plan.(4)Taking pile length,pile diameter and pile spacing as the influencing factors,and the post-construction differential settlement as the evaluation index,design orthogonal test,it is obtained that the significance of each influencing factor and gired the optimal combination.Finally,SPSS software is used to fit the regression equation between PHC pipe pile length,pile diameter,pile spacing and post-construction differential settlement in densification section and transition section.