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Title: Lattice leg effects in the penetration and bearing behaviour of spudcan foundation
Authors: LI YUPING
Keywords: Spudcan, Lattice leg, Centrifuge, FEM, Long-term, Punch-through
Issue Date: 20-Dec-2013
Source: LI YUPING (2013-12-20). Lattice leg effects in the penetration and bearing behaviour of spudcan foundation. ScholarBank@NUS Repository.
Abstract: In deeply penetrated spudcans, the lattice legs may interact with surrounding soil during spudcan installation, thereby influencing its cavity formation and vertical bearing capacity. This research work focuses on the effect of lattice legs on the vertical performance of spudcan foundations in both single clay layer and loose sand overlying normally consolidated clay. Centrifuge model tests were conducted to model transient spudcan penetration affixed with different lattice legs. Both normally consolidated and over-consolidated clays are examined. The lattice leg serves to partially restrict the influx of the backflow soil on top of the spudcan. Cavity formation is influenced by the presence of the lattice leg as well as the soil state of consolidation. The results show that spudcan footings affixed with lattice legs exhibit increased vertical penetration resistance and enhanced bearing capacity, compared to those without. The effect appears to vary with the opening ratios and area ratios of the lattice leg. Effective-stress finite element analysis was performed to verify and extend the parametric range beyond that of the centrifuge model tests. The effects of lattice leg on foundation failure mechanism, cavity formation and vertical bearing capacity were investigated. The foundation failure mechanism is influenced by the presence of the lattice leg. Based on the finite element analysis and centrifuge model test results, a relation between the inner cavity depth and soil strength profile, spudcan diameter, opening ratio and area ratio of lattice leg is proposed. The undrained effective-stress finite element analysis shows a good prediction of the measured load-penetration response from centrifuge model test; this validates its feasibility in modelling the vertical performance of spudcan foundation. The long-term bearing behavior of spudcan foundation was investigated by centrifuge model tests. The long-term penetration resistance increases rapidly during re-penetration, and is much larger than that in short-term. It is also influenced by the presence and type of lattice leg. The finding suggests that it may be possible to estimate the post-consolidation bearing capacity of spudcan foundation by using the long-term bearing capacity factor at 0.1D re-penetration depth, which is approximately 1.5 times the short-term bearing capacity factor for spudcan with typical lattice leg. Arising out of the study on lattice leg, the possibility of using a top-mounted skirt on the spudcan to mitigate or eliminate punch-through failure of spudcan foundation in loose sand overlying normally consolidated clay was examined using centrifuge model test. Top-mounted and downward skirts are both useful separately for reducing punch-through depth, although they work via different mechanisms. When the two kinds of skirts are combined in the right way, they can confer very significant reduction in punch-through depth.
Appears in Collections:Ph.D Theses (Open)

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