Consolidation integrated buoyancy model for marine clay improvement using polyurethane foam
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Date
2020-12
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Universiti Teknologi Malaysia
Abstract
An alternative lightweight material known as polyurethane (PU) foam is used for ground improvement work of road foundation. The ground improvement work is executed by partially excavate and remove the soft soil at shallow depth, then replace with PU foam. The stiff PU foam assists to distribute evenly the overburden load to the underlying soil and subsequently prevent the differential settlement. In addition, buoyant force and hydrostatic pressure are produced by PU foam on saturated clay which assist to further reduce the soil settlement. In this study, laboratory consolidation test utilizing Rowe Cell apparatus was carried out to determine the consolidation settlement incorporated buoyancy behaviour of PU foam partial replacement on marine clay soil and on water, respectively. In addition, a Constant Rate Strain test (CRS) was carried out to evaluate the effect of different percentage of water content in soil for the improved marine clay to the upward and downward displacement of soil. Buoyant force was also determined from the CRS test on PU foam immersion in water. The percentage thickness of PU foam to the initial soft clay layer and water varies from 15% to 80%. The Rowe Cell test results indicate that for PU foam partial replacement on water, the downward displacement is much lesser compared to the settlement for PU foam replacement on marine clay. Consolidation settlement for improved marine clay reduces significantly compared to the untreated condition. In addition to the reduction of soil weight due to part of the soft soil is replaced by lightweight PU foam, the presence of water content in the saturated clay assists to further reduce the overburden load imposed on the soil due to buoyant force that has been produced. CRS test results indicate that the buoyant force is equivalent to the weight of water displaced by PU foam which is in line with Archimedes’ principle. The settlement is significantly reduced with the increasing thickness of PU foam as more water is displaced by PU foam. The finite element model using PLAXIS 2D was executed to verify laboratory test results and both results show good agreement with each other with different tolerances of less than 20% in terms of consolidation settlement, buoyant force and excess pore pressure. An alternative equation on the consolidation settlement integrated buoyancy model for the ground improved with PU foam was produced in this research. The settlement value was compared with the allowable settlement criteria for road construction on soft clay by Public Work Department (PWD). The optimum percentage of PU foam to the initial soft clay thickness with the flow chart application procedure were adopted in this study. For deep marine clay, the initial soft clay thickness depends on the significant depth of the clay thickness at which the soil does not contribute to the settlement of foundation. The optimum percentage of PU foam thickness required for road work is less than 20% of the initial soft clay thickness. As a conclusion, PU foam replacement at shallow depth of soft marine clay is an effective ground improvement method in solving excessive and differential settlement problem for road construction on soft marine clay.
Description
Thesis (Ph.D (Civil Engineering))
Keywords
Polyurethanes