Study On “soil Arching” Characteristics And Fixed-geosynthetic Technique In Geosynthetic-reinforced Pile-supported Embankments

A new ground improvement technique,referred to as fixed geosynthetic-reinforced permeable pile-supported（FGP）technique,is proposed.Numerical simulation and theoretical analysis are employed to study the performance of FGP embankments.“Soil arching”,as the main medium of load-transfer for a GRPS embankment,has significant influences on the load-transfer and deformation charateristics.A series of numerical models by discrete element method（DEM）were established to investigate“soil arching”characteristics.The main contents are presented as follows:（1）The load transfer,deformation and interface friction of geosynthetic have been comparatively analyzed for two kinds of reinforcement techniques,i.e.,fixed geosynthetic-reinforced pile-supported（FGR）technique and conventional reinforced piled（CR）technique.The results indicated that the deformation curve of geosynthetic can be described with ellipse for CR technique.A calculation method of tension in the geosynthetic has been proposed,the presented method was verified with numerical simulation results to investigate its validity.（2）A two-dimensional numerical simulation by coupled mechanical and hydraulic modelling is conducted to investigate the mechanism of FGP embankment by analyzing settlement,lateral displacement,geosynthetic tension and excess pore water pressure distribution and dissipation.The results showed that the new embankment structure can reduce the excess pore water pressure,promote dissipation of excess pore water pressure and efficiently reduces the total and post-construction settlement.（3）A series of numerical models by discrete element method（DEM）were established with the particle flow code PFC^2D to investigate the characteristics of“soil arching”.Numerical results indicated that the“soil arching”develops gradually with the increase of pile-soil relative displacement and finally maintains a relatively stable state.Meanwhile the relatively stable“soil arching”is roughly parabola-shaped with a height of 0.8 times of cap beam clear spacing.Additionally,the embankment height has significant influences on the feature and evolution of“soil arching”.However,the type of embankment fill,the cap beam clear spacing and cap beam width have insignificant influences on the characteristics of“soil arching”.（4）The analysis method of soil arching effect was improved based on H&R soil arching model by introducing the state parameter of soil element at arching crown or pile head.The improved method not only considered the elastoplastic state of soil element at arching crown or pile head,but also ensured the equilibrium condition of embankment load.