Jiang Tao Yi

Centrifuge Study of the Effects of Lattice Leg on Penetration Resistance and Bearing Behavior of Spudcan Foundations in NC Clay

This paper reports the primary results of a centrifuge model study into the possible effects of the lattice leg on the penetration resistance and vertical bearing capacity of spudcan foundations in normally consolidated clay. Up to now, the possible effects of the lattice leg has been largely ignored in both research and design of spudcan foundation. Centrifuge experimental results show that there is an increase in penetration resistance for spudcan footing equipped with lattice leg, in comparison with spudcan footing connected to slender circular column leg as widely used by current research. Larger excess pore water pressure was generated by the spudcan penetration with lattice leg in compare with that without. Moreover, the presence of the lattice leg is shown to affect the cavity depth formed around the penetrated spudcan footing, which is simply assumed completely back flow for spudcan penetration in soft clay by SNAME (2008). It was found that the bearing capacity of spudcan foundation has been further underestimated by SNAME (2008) due to the neglecting of lattice leg effect. Taken altogether, this implies that changes in penetration resistance arising from the lattice leg may be due to the effect of the latter on the backflow pattern. Apart from highlighting the effect of the sleeve with big openings, the results also highlight the possible future use of sleeves to enhance the bearing capacity and possibly reduce the penetration of spudcan foundations in various soil deposits.Copyright

Effective-Stress Finite Element Analysis of Spudcan Penetration

The numerical modeling of spudcan penetration involves technical challenges posed by large soil deformation coupled with significant material non-linearity. The Lagrangian approach commonly used for solid stress analysis often does not work well with large deformations, resulting in premature termination of the analysis. Recently, the Arbitrary Langrangian Eulerian (ALE) and the Eulerian methods have been used in spudcan analysis to overcome problems caused by the soil flow and large deformation. However, most of the reported studies are based on total stress analysis and therefore shed no light on the excess pore pressures generated during spudcan installation. As a result, much remains unknown about the long-term behaviour of spudcans in the ground, which is affected by the dissipation of excess pore pressures. This paper reports an effective-stress finite element analysis of spudcan installation in an over-consolidated (OC) soft clay. The Eulerian analysis was conducted using ABAQUS/ Explicit, with the effective stress constitutive models coded via the material subroutine VUMAT. The results demonstrated the feasibility of conducting effective-stress finite element analysis for undrained spudcan penetration in OC clays. The paper discusses the flow mechanism, stable cavity depths and bearing capacity factors when spudcan installation occurs in various OC soils. It was found that the pore pressure build-up concentrates in a bulb-shaped zone surrounding the spudcan. The size of the pore pressure bulb increases with increasing penetration. The maximum excess pore pressure, which is generated near the spudcan tip, is predominantly controlled by the undrained shear strength at the tip level.Copyright

A two-phase coupled Eulerian-Lagrangian FEM for offshore spudcan analysis

This paper reports a development of a two-phase coupled Eulerian-Lagrangian FEM for analyzing the short-and long-term response of offshore spudcan footing. The proposed method is composed of three integral components which are effective stress Eulerian analysis for the shrot-term installation behavior of spudcan, mesh-to-mesh solution variable mapping and coupled-flow Lagrangian analysis for the post-installation, long-term working behaviour of spudcan. By combining the advantages of Eulerian and Lagrangian finite element methods, this coupled Eulerian-Lagrangian FEM is tailored to solve offshore foundation problems which often see rapid and large-scale undrained soil flow during installation followed by much longer periods of embedment in the ground during operation.