Research On Dynamic Response Of Bridge-Approach On CFG Pile Composite Foundation Of Highway

Due to the large difference between the roadbed filling and the abutment stiffness,the vertical settlement difference between the subgrade and the abutment under the continuous action of external traffic load and self-weight load causes the vehicle body to jump when the vehicle passes at high speed,that is,the bridge head jumps phenomenon.Jumping at the bridgehead is a common disease problem in highway engineering.It is more prominent in the land reclamation area,which not only threatens driving safety,but also causes damage to the pavement structure and increases the cost of road maintenance.This paper takes the CFG pile composite foundation road and bridge transition section as the research object,and selects the bridge head stagger height,the vehicle body vertical acceleration,the weighted acceleration mean square value,the vehicle dynamic load coefficient,the vertical displacement difference of the front and rear wheels,and the vehicle pitch angle as the transition section Evaluation indicators;Abaqus software was used to establish CFG pile composite foundation transition model,including subgrade model,CFG pile composite foundation model,7-degree-of-freedom vehicle model and bridge model;the cumulative settlement of CFG pile parameters and vehicle parameters on the transition subgrade was studied In consideration of the influence of driving dynamic response,an optimized design scheme for longitudinal pile placement in the transition section is proposed;a pavement superimposed excitation model for the transition section settlement at different levels of pavement is established,and the driving dynamic response of the transition section under uneven road conditions and CFG are studied The effect of piles on improving ride comfort.The specific research conclusions are as follows:(1)The CFG pile can reduce the cumulative settlement of the roadbed in the transition section and improve the bridge head jump.Reducing the pile spacing has the most significant effect on reducing the cumulative settlement of the subgrade,and the effect of increasing the elastic modulus of the pile body is the worst.Increasing the pile diameter and reducing the pile spacing have a significant improvement effect on the bridgehead jump.When the pile diameter is greater than 0.4 m,the improvement effect of increasing the pile diameter on the vehicle dynamic response is weakened.When the pile spacing is 1.4 m,the peak vertical acceleration of the car body The occurrenceposition is offset from the near bridge end to the far bridge end;increasing the pile length and increasing the elastic modulus of the pile body is not obvious.(2)The length of the transition section should not be shorter than the length of the vehicle.The longer the transition section,the smaller the vibration of the car body and the better the riding comfort;under the same transition section conditions,the faster the driving speed,the more severe the vibration of the vehicle body.The stronger the impact,the smaller the effect on the vertical displacement difference between the front and rear wheels and the pitch angle of the vehicle.The vibration of the vehicle body under load is less than the no-load condition.The difference between the maximum vertical displacement of the front and rear wheels and the pitch angle of the vehicle are very small.Under the premise,the vehicle should be driven without load,so as to reduce the hazards caused by jumping at the bridge head.(3)The CFG pile plane parameter optimization design can make the transition section and the adjacent structure stiffness transition more gentle.Both the variable pile diameter scheme and the variable pile spacing scheme can reduce the vehicle dynamic response,but the evaluation index values of the variable pile spacing scheme are better than the variable pile diameter scheme.Therefore,this article recommends the use of longitudinal variable pile spacing layout optimization design.(4)When the settlement of the transition section of Class A,Class B and Class C pavement occurs,setting CFG piles can alleviate the bridge head jump to a certain extent.When the direct settlement and staggered settlement occur in the transition section,it is not conducive to the smooth driving of the vehicle,while the broken-line settlement and the curved settlement have improved the bridgehead jump to a certain extent,and the curvilinear settlement has the best improvement effect.