Reliability Evaluation of Compacted Lateritic Soil Treated with Bagasse Ash as Material for Waste Landfill Barrier

Abstract

Laboratory tests were conducted on a reddish brown lateritic soil treated with up to 12% bagasse ash to evaluate its suitability in waste containment barriers applications. Numerical analysis, using the First Order Reliability Method (FORM), was done to estimate the reliability of regression model for predicting hydraulic conductivity of the soil bagasse ash mixes based on laboratory results obtained. Based on the reliability (FORM) results, compactive effort, initial degree of saturation, bagasse ash contents and percentage fines are critical variables that must be controlled in achieving low hydraulic conductivity in the field. The model can be used in preliminary screening of borrow source materials that would meet acceptable hydraulic conductivity. INTRODUCTION Compacted fine-grained lateritic soils treated with up to 12% bagasse ash have been shown to have good hydraulic properties in waste containment facilities as barrier to water and contaminant flow (Osinubi and Eberemu, 2013); but a major problem facing the analysis of pollutant migration through compacted soils is the heterogeneity of hydraulic properties of compacted soils. They could be spatially variable and can fluctuate significantly within short distances (Rogowski, 1990). By probabilistic modelling, incomplete knowledge of these hydraulic properties and associated uncertain properties of soil can be mathematically incorporated into an analysis (Benson and Daniel, 1994). The effect of randomness in local properties typically hydraulic conductivity (which might result from randomness in soil properties and variability in compaction and moisture content during placement), upon the spreading of contaminant plumes needs to be understood. For compacted soil liners, a design hydraulic conductivity value of K = 1 x 10 m/s is typically specified. However this is not always achieved in the field (Daniel, 1984). This is so because of spatial variability of soil properties such as hydraulic conductivity; laboratory and field measurements which are not accurate indicators of full scale liner performance. Moreso, the compaction control parameters such as dry density and water content are always subject to uncertainties. 911 Geo-Congress 2014 Technical Papers, GSP 234 © ASCE 2014