Research On Differential Settlement Characteristics And Calculation Method Of Transition Section Of Expressway Soft Ground Treatment

There are many methods and forms of expressway soft soil foundation treatment.In order to avoid vehicle jumping at the bridge head,the composite foundation method is often used to connect the bridge head,but the general subgrade is often treated by drainage consolidation method.The transition section of the two treatment methods may cause large differential settlement,especially in areas with thick soft soil layers such as coastal and riverside.In view of this,taking the typical expressway project in Zhejiang Province as the research object,this paper studies the differential settlement deformation characteristics and settlement correction calculation method of the transition section through field investigation and numerical analysis.The main research contents and results are as follows:A representative expressway project in Zhejiang Province is selected to investigate the treatment and effect of the transition section through data collection,field investigation and post construction settlement analysis and prediction.The transition between plastic plate and mixing pile section with shallow soft soil is good;When the pile length in the transition section changes greatly,there are transverse tensile cracks and obvious settlement in the pavement.The settlement difference between the pipe pile and the plastic plate section is large,and there is an obvious secondary jumping phenomenon.The finite element model of the transition section between cement mixing pile and plastic drainage board along the road is established,and the consolidation deformation characteristics of soil and the stress condition of cement mixing pile are analyzed.There is still large excess pore water pressure at the lower part of the cement mixing pile area,which has not dissipated,resulting in large consolidation settlement after construction.Due to the large consolidation settlement in the early stage,the cement mixing pile near the plastic drainage board also has a large horizontal displacement.The settlement deformation law of the transition section and the variation law of the transverse force of the mixing pile under the conditions of different filling height,soft soil depth and pile spacing are analyzed.The filling height has the greatest influence on the subgrade settlement and horizontal displacement,followed by the mixing pile spacing.The influence of the soft soil depth is small,but the settlement difference is large under the conditions of penetration and non penetration.With the increase of pile spacing,the overall horizontal displacement of the pile body in the cement mixing pile area towards the drainage consolidation area shows that the consolidation settlement of the plastic drainage plate will affect the lateral consolidation of the composite foundation area.Combined with the settlement characteristics of the transition section of bridge head foundation treatment,a calculation formula of correction coefficient considering threedimensional consolidation characteristics is proposed,which provides a new idea and reference for the settlement calculation of the transition section.