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Title: Stabilisation of an excavation by an embedded improved soil layer
Keywords: excavation, soft soil, improved soil, untreated soil gap, berm, centrifuge
Issue Date: 26-Feb-2004
Citation: GOH TEIK LIM (2004-02-26). Stabilisation of an excavation by an embedded improved soil layer. ScholarBank@NUS Repository.
Abstract: The behaviour of an excavation in soft ground stabilised by an embedded improved soil layer was studied using the centrifuge modelling technique. Instrumented field studies are difficult considering the fact that the true mobilised stiffness of the improved soil is not known. For an accurate centrifuge study, it is necessary to carry out in-flight excavation, a capability available to only a handful of centrifuges in the world. The results from centrifuge studies were also interpreted using finite element studies. This combination offers an opportunity to interpret detailed numerical results, which were checked against actual experimental data when feasible. The main focus of this study is to provide an in-depth understanding of the various mechanisms involved for three different configurations of soil improvement, namely an improved soil strut, an improved soil strut with a small gap next to the retaining wall (a problem in actual construction) and an improved soil berm (to reduce cost). Typically, in design, an equivalent uniform strut is used. But through this study, it was found that the mechanisms involved in each configuration are distinctively different. In a strut, the resistance is transmitted from wall to wall whereas in a berm, the resistance is provided by the end bearing and interfacial shear. For a strut with a gap, the length and stiffness of the gap have a major impact on the overall mobilised stiffness. The stiffness of the gap itself was found to be influenced by the amount of overburden above it and thus is a function of the depth of excavation. A simple combined spring model allowing for a variation in spring stiffness with overburden was shown to be able to provide a consistent explanation of this trend. Finally, the study showed that for an improved soil strut, a higher stiffness would result in a smaller movement but a much higher bending moment. In current design practice, this fact is seldom factored in, and some serious thinking is needed to ensure a safe design.
Appears in Collections:Ph.D Theses (Open)

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