Reliability Evaluation of Hydraulic Conductivity Characteristics of Waste Wood Ash Treated Lateritic Soil

Abstract

Probabilistic reliability analysis of suitability of compacted waste wood ash (WWA) treated lateritic soils for use as liners and covers in waste containment structures was assessed using FORTRAN-based First Order Reliability Method. This is based on the predictive model developed from regression analysis and statistical analyses (descriptive statistics and regression) of the results of geotechnical properties of both natural and WWA modified samples in which WWA, water content (WC), percentage fine, plasticity index (PI), degree of saturation (Sr) and compactive effort are the independent variables and hydraulic conductivity (k) the dependent variable. In sensitivity, reliability indices (β) decreased with variations in the coefficient of variation for all the variables at West African Standard and British Standard Heavy (BSH) compactive efforts, but increased at British Standard light except WWA which has no effect by remaining constant. Also, reliability indices increased with increase in compactive efforts. However, apart from WWA, PI has the most significant influence in sensitivity followed by Sr and then WC. Analysis of variance showed that compactive effort has significant effect on the outcome of the results. Stochastic assessment of the reliability indices shows that none of the variables has the reliability index values between 2.5 and 4.0 which is the safety margin in structural reliability; however, the use of reliability index value of 1 according to NKB Report (Recommendation for loading and safety regulations for structural design. Nordic Committee on Building Regulation 1978) was favourable only at BSH compactive efforts. Therefore, only BSH could be used successfully to actualize reliable minimum hydraulic conductivity of 1 × 10−9 m/s in the field using WWA treated lateritic soil.