Numerical Study of Pile Supported Embankment Resting on Layered Soft Soil: Fid-Bau Portal

Numerical Study of Pile Supported Embankment Resting on Layered Soft Soil

Azim, Uzma / Sengupta, Siddhartha

Adaption of construction on soft soil is coming into the picture with the increased demand for developing infrastructure. Since soft grounds are characterized by low permeability and high compressibility as well as low shear strength, the construction needs to be accompanied by ground strengthening methods. This paper studies settlement study of a 4 m high pile supported embankment resting on layered soft soil with respect to change in depth of pile penetration, the influence of altering slope and geometry of the embankment, effect of varied pile spacing and surcharge, variation of mesh size involved in simulation and effect of simulating model. Commercially available finite element software PLAXIS-2D was employed in the investigation. Increasing the depth of penetration of piles from 6 to 9 m resulted in a deduction in maximum displacement in the underneath soft soil layers from 0.3052 to 2.982 m due to transmission of load to a comparatively deep stiff soil layer. Decreasing the spacing between the piles from 4 m c/c spacing to 2 m c/c spacing, lowered the deformation in the soft soil layer and the time taken for consolidation due to homogenization of soil particles caused due to surcharge load and efficient load transfer platform in combination with friction acting on the surface of the piles. Also, widening the embankment and increasing the number of piles resulted in a decrease in the total displacement because of the larger area endured under an efficient load transfer platform. With regard to mesh size, fine mesh types with r_e of 0.50 gave accurate output but resulted in increased computational time due to the involvement of higher densification of elements. Therefore, a medium mesh size composed of r_e equivalent to 1.00 was employed in order to obtain desirable results in nominal time. Modified Cam Clay model (MCC) and Soft Soil model (SS) were used to perform a comparative study to observe the characteristics of soft soil with respect to the total displacement and dissipation of excess pore pressure. The total displacement when Modified Cam Clay (MCC) model was used to simulate the problem was 0.3052 m; modeling with the Soft Soil (SS) model with decreased stiffness resulted in an over prediction of the settlement to almost 3.154 m. This was attributed to the difference in the way Modified Cam Clay (MCC) and Soft Soil (SS) model represented the failure surface on the left side of the critical state line and also on the modification in the compression indices involved in the calculation of simulating parameters. Further, the MCC model incorporates the capability of modeling the elasto-plastic behaviour of the soil medium which assists in efficiently analyzing the simulated model under hardening, softening and critical state behaviour.