Finite Element Numercial Simulation Of Embankment On Deep Soft Ground Treated By Bag Sand Wells Joint With Dry Jet Mixing Piles

China has a vast territory,complex and diverse geology condition,and the distribution of soft soil is extremely extensive.With the promotion of the strategy of "China’s strength in transportation" and "The Belt and Road",the construction of highways and railway projects on deep soft soils is increasing.Because soft soil has the characteristics of high water content,large void ratio,low shear strength,high compressibility,slow consolidation and creep,it will cause excessive settlement,even instability of the foundation under the action of the embankment,which greatly threatens the safety of transportation,and huge losses in manpower and material resources.The drainage consolidation method and the dry jet mixing method were developed in the last century,their theory and design methods have been relatively mature,but both methods have their own disadvantages.Although the comprehensive treatment approach which combines the two methods mentioned above has been applied to a certain degree in engineering,there are still few in-depth studies on its treatment effect,mechanical mechanism,and design optimization.Based on research at home and abroad,combined with the results of centrifugal model tests carried out by predecessors,refined numerical simulation of embankment on deep soft soil treated by bagged sand wells and dry jet mixing piles comprehensively was conducted considering soft soil creep,dynamic filling of embankment layer-by-layer,soil-structure interaction,etc.The treatment effect and mechanism of deep soft soil foundation were discussed.The main work carried out is as follows:(1)Based on the PLAXIS 3D software platform,the key technologies in finite element modeling such as the numerical realization of the three-dimensional Biot consolidation theory,the reasonable selection of soft soil constitutive models,the scientific simulation of bagged sand wells and dry jet mixing piles,etc.were introduced.The soft soil creep model is adopted to describe the mechanical behavior of soft soils.Solid replacement and interface elements are applied to simulate dry jet mixing piles and pile-soil interactions respectively,and "drainage lines" elements are used to simulate bagged sand wells.(2)Using PLAXIS 3D software,based on the three-dimensional Biot consolidation theory,and relying on geotechnical centrifugal model tests carried out by predecessors,a numerical model for comprehensive treatment of embankment on soft soil treated with bagged sand wells and dry jet mixing floating piles was constructed.The comparison of the results obtained from numerical model and geotechnical centrifugal model,including the settlement and lateral displacement of the foundation confirms the reliability of the established numerical model,thus laying a good foundation for the subsequent in-depth and comprehensive analysis.(3)Based on the numerical model verified and calibrated with the results of centrifugal model tests,four working cases were discussed,including no treatment measures,only bagged sand well treatment,only dry jet mixing piles treatment,and bagged sand well and dry jet mixing piles comprehensive treatment.The distribution rules of soft soil foundation settlement,lateral deformation,embankment top surface settlement,etc.were discussed.The mechanical mechanism of the soft foundation treated by bagged sand well joint with dry jet mixing piles was revealed from the perspectives of excess pore water pressure,pile-soil stress,etc.The whole evolution of the soil arching effect for the soft foundation treated by the floating piles was explored.(4)The two core issues of the comprehensive treatment with bagged sand wells and dry jet piles for embankment on deep soft soil were further discussed,including the impact weight relationship of the bagged sand wells and dry jet mixing piles on embankment settlement,and the sensitivity of the core design parameters of dry jet mixing piles to the post-construction settlement of embankment,which can provide valuable reference for the design and construction of embankment on soft soil comprehensively treated by bagged sand well and dry jet mixing piles.