Analysis Of Working Characteristics And Stability Of Pile-supported Reinforced-earth Wall For Embankment Widening

With the rapid development of economy,bi-directional and four-lane freeway cannot satisfy the needs of increasing of traffic,especially in soft soil area of southeast coast of China.Subgrade widening is an important approach to improve the traffic capacity.Aiming at the problems in the existing subgrade widening methods,such as occupation of large area,high cost of ground improvement and large demand of fill,the Pile-Supported Reinforced-earth Walls(PSRW)constructed after slope cutting with the slope ratio of 1:0.5~1:1 is put forward.The main contents and results are presented as follows.(1)The superiority of the new widening scheme was verified by the finite difference model.Numerical models of four subgrade widening methods,including reinforced embankment,reinforced-earth wall,pile-supported reinforced embankments and pilesupported reinforced-earth wall,were built for the subgrade settlements comparison.The results indicate that the PSRW method could reduce the ground settlement of existing subgrade and the differential settlement between the new subgrade and existing subgrade effectively.(2)As the complexity of after PSRW,Based on the strength reduction method and displacement diversity factor,the dynamic development law of filling,geogrid,pile and retaining wall and the influence of these factors on the embankment stability were discussed due to the complex structure.The impact degrees of these factors were also investigated.The results show that the larger the slope ratio,the higher the stability is.With the increase of the strength reduction factor,the stress of reinforcement increases,the subgrade is not destabilized.However,the bending failure of the pile induces the instability of the subgrade.The retaining wall overturns as a whole.(3)There are multiple failure modes of piles under the embankment.The numerical model considering the different post-failure behaviors was adopted to analyze the antisliding mechanism and failure modes of piles at different locations.The stress and deformation characteristics,failure modes and failure mechanism of embankment with different bending stiffness and strength,pile spacing and soil distribution were studied.The influences of the spacing of reinforcement and the slope ratio on embankment stability were also analyzed.Each pile under embankment is progressively damaged.After widening,the piles under embankment can be divided into the bending shear piles,the bending piles and the bearing piles.(4)Based on the research of the failure mechanisms of the embankments,the comparison among several stability analysis methods relative to different failure modes was conducted.It is suggested that safety factor obtained by the embankment stability analysis method considering the different failure modes of piles is reliable.