TIME-DEPENDENT PERFORMANCE OF COLUMN-SUPPORTED EMBANKMENTS INVOLVING VISCOUS REINFORCEMENT AND PREFABRICATED VERTICAL DRAINS
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A fully 3D coupled finite element (FE) analysis is performed to examine the performance of four sections of a full-scale embankment on soft soils. The proposed FE model successfully captures the behaviour of full scale embankments involving geosynthetic-reinforced and piled sections, and the observed difference in performance of different improvement techniques, with respect to pore-water pressures, settlements, subsoil stresses, lateral displacements below the toe of the embankments, and reinforcement strains. The effects of geosynthetic reinforcement and multi-layers of reinforcement on the performance of the pile-supported embankment are discussed. The relative load transfer is calculated using eight existing methods and they are compared with the field measurements and numerical results. Deep-mixing-method (DMM) columns which are less rigid than piles are increasingly used as a cost-effective soft ground improvement technique. The influence of reinforcement viscosity on the post-construction performance of embankments with DMM floating columns and fully penetrating columns is investigated using the 3D FE coupled model verified by aforementioned field case. It is shown that the viscous behaviour behaviour of geosynthetic reinforcement can increase the long-term shear deformations of foundation soil and also the horizontal toe movement. The DMM column-supported embankments with viscous and with inviscous reinforcement are numerically constructed to identify the effect and magnitude of reinforcement creep and stress relaxation. It is shown that consideration of time-varying subsoil hydraulic conductivity has an important effect on time-dependent embankment behaviour particularly with respect to horizontal toe movement of reinforced and DMM floating-column supported embankments under working conditions. The potential interacting factors of the construction rate, column stiffness, column spacing, column type (floating and fully penetrating), reinforcement stiffness, and different foundation soil profiles are explored. The results show that there can be large residual (post-construction) crest settlement and a lengthy consolidation period for reinforced embankments with floating columns. Finally, the short-term and long-term performance of reinforced, DMM floating-column supported embankments with and without prefabricated vertical drains (PVDs) are investigated. The inclusion of PVDs is found to address the aforesaid issues. Also, the synergistic effects of PVDs and surcharge are examined for a bridge approach embankment.