Long-term consolidation analysis of a large-scale embankment construction on soft clay deposits using an elasto-viscoplastic model

In this paper, the consolidation analysis of a large-scale embankment construction in Osaka City is presented, where a conventional levee with a height of about 8 m has been extended to a super levee with a total width of 215 m. The ground consists of alluvial sandy layers and soft clay deposits, which have been locally improved by several methods, including deep mixing beneath the conventional levee and the combination of sand drains and sand compaction piles under the extended back slope. A long-term consolidation analysis of this super levee construction is carried out using an elasto-viscoplastic constitutive model. The layered construction procedure is applied to properly simulate the construction sequence of the super levee. The effects of the structural degradation and the strain dependency of the shear modulus, as two aspects of destructuration in clay materials, are studied in terms of the consolidation behavior for the unimproved case. For the improved case, the analysis is implemented by including the ground-improved zones in the finite element simulation. The field observation data obtained during the preloading process, before the construction of the super levee, are employed to verify the assumptions and to calibrate the material properties of the improved layers. The effects of destructuration in the natural ground cases are observed as excess pore pressure build-up after construction and strain localization. The effects of ground improvement techniques are studied through a comparison of the deformation results and the excess pore water pressure responses with the natural ground cases. The numerical results show that it is important to carefully estimate the unequal long-term settlement for the construction of large-scale embankments.