Study On Stability And Control Strategy For Geosynthetics-reinforced Column-supported Embankments

In recent years,great development of highway and railway in soft ground has been witnessed in China.Embankments are necessary to bring the highway and railway up to functional elevations.Such embankments,if placed on highly compressible soft soil,may experience bearing capacity and stability problems.Column technologies and geosynthetic reinforcements are often separately employed to reduce total and differential settlements,to speed consolidation,and to improve the stability.Besides,geosynthetic-reinforced column-supported embankments(GRCSEs)are applied widely in the geotechnical engineering,especially highway or railway.The combined treatment with column technologies and geosynthetic reinforcement can effectively enhance bearing capacity and stability of embankment.The current design method for GRCSE system mainly assumes that a simultaneous shear failure of the columns and a rupture of geosynthetic reinforcement along the failure slip.However,some case histories of instability of the embankments have occurred due to irrationality of the existing stability analysis methods.In this study,centrifuge tests,numerical modelling and analytical solution were adopted to investigate the failure mechanism and control strategy of GRCSE system.The main contents are as follows.(1)The failure mechanism and stability analysis of flexible column-supported geosynthetic-reinforced embankment(e.g.,stone column)is investigated.Based on an upper-bound limit state plasticity failure discretization method,a design chart of stability of stone column-supported and geosynthetic-reinforced embankments for preliminary engineering design is developed in consideration of both bond failure and rupture failure of geosynthetics.The relationships between the stability of stone column-supported and geosynthetic-reinforced embankments and various influencing parameters,including the soil strength,geometric configuration,reinforcement strength,and area replacement ratio,are analysed.To provide a theoretical solution for engineering design,an approach based on the limit equilibrium method is proposed.(2)Semi-rigid columns(e.g.,deep mixing(DM)columns)have been widely adopted to improve the stability of GRCSEs system and the corresponding failure mechanism are investigated.Based on a finite difference approach incorporated in the FLAC3 D,a damage plasticity model that considers the brittle failure behavior of columns and the rupture failure behaviour of geosynthetic reinforcement are proposed,respectively.The progressive failure of semi-rigid columns from various rows and a transition of failure mechanism in various configurations are revealed.The interaction of columns,geosynthetics and soils and the influence of geosynthetic on failure mechanism of columns are investigated.Based on the interaction,a reasonable design based on a failure mechanism could be suggested.(3)Rigid columns(e.g.,concrete columns)have been widely adopted to improve the stability of GRCSEs system and the corresponding failure mechanism are investigated.Centrifuge test and numerical modelling are used to analysis the two failure modes of rigid columns,i.e.,internal failure and external failure,and the instability of GRCSEs.The analysis reveals the influence of stiffness,layer of geosynthetic on stability of GRCSE system.The results show that the progressive failure bending failure of columns contributes to the instability of GRCSE.The contribution of geosynthetics to resisting progressive failure of rigid columns is analysed with the distribution of internal forces of columns from various rows and tensile strain of geosynthetics under embankment load.The effectiveness of geosynthetic stiffness on improving the embankment stability when the underlying stratum is inclined is investigated and a reasonable design could be suggested.