Behavior of Sarawak Clayey Soil using Various By-Product Additives Stabiliser for Potential Subgrade Materials
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UNIVERSITI MALAYSIA SARAWAK
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Due to rapid development and scarcity of land with good and desirable soil for civil infrastructure, the development projects shifted to the site with problematic soil such as soft soil. Construction of pavement subgrade layer with soft soil is hampered by their low strength and high deformability which causes difficulties such as stability deficiency and high settlements which exhibit insufficient strength to support the pavement traffic loading. Chemical stabilisation of clay soils in Sarawak using Fly Ash (FA), Rice Husk Ash (RHA) and Palm Oil Fuel Ash (POF A) was carried out due to their potential benefit to improve engineering properties of weak subgrade soil through cementitious products. Three different soils from Sri Arnan, Serian and Kuching divisions were collected and considered in this study to represent a range of subgrade soil in Sarawak based on different clay content. All tested clay soils are categorised as high plasticity silty clay. The effect of FA, RHA and POFA activated by cement in stabilised clay soils was investigated via laboratory testing. The density-moisture content relationship was evaluated via compaction test to obtain the maximum dry density (MDD) and optimum moisture content (OMC) for the natural soil and ashes stabilised soils mixture. For the FA stabilised soils, the MDD and OMC increased and .~ decreased respectively with increased FA dosage. The MDD and OMC were decreased and increased respectively for RHA and POF A stabilised soil with increased ashes dosage. The selection of the optimum mix proportion was determined based on the unconfined compressive strength (UCS) test results that satisfied targeted compressive strength and highest compressive strength achievement with convenient curing period for the field site. Based m the results, optimum mix proportion for FA, RHA and POF A stabilised soils were 40% FA+ 6% cement, 40% RHA+ 6% cement and 40% POFA+ 6% cement at 28 days curing period. The natural and selected optimum mixture stabilised soils were tested under static triaxial compression test for both isotropic consolidated undrained (lCU) and isotropic consolidated drained (lCD) condition. The deviator stress increased with increased of confining pressure. Effective cohesion and effective internal friction angle also increased significantly for the ashes stabilised soil compared to the natural soils. Besides, the natural and selected optimum mixture stabilised soils were tested under California Bearing Ratio (CBR) to regulate the bearing capacity under unsoaked and soaked condition. The bearing capacity of the optimum mix proportion ashes stabilised soils recorded remarkable improvement compared to the bearing capacity of the natural soil. The CBR value for the ashes stabilised soil had even achieved the minimum requirement for the stabilised subbase layer required by Arahan Teknik Jalan, Malaysia. Pavement modelling was performed via finite element analysis (FEA) and found that vertical deformation decreased when ashes stabilised soil utilised as subgrade material in the pavement structure. Besides, a minimum of 400 mm thickness of FA, RHA and POF A stabilised soil is recommended to be implemented in subgrade layer to achieve lower deformation compared to the natural soil as total subgrade material. To add, by omitting the subbase layer, the stabilised Serian and Kuching soils preferable 500 mm in thickness. Through column leaching test (CLT), most of the heavy metals leached out from the ashes stabilised soils are within the permissible range and the ashes stabilised soils are found safe to be used in the field with negligible environmental risk. The results presented herein confirm that utilisation of the by-product FA, RHA and POF A can certainly be useful, both in improving the strength of weak subgrade soils and in saving the environment from a significant potential pollutant.