Reliability Estimates of Field Hydraulic Conductivity of Compacted Bagasse Ash Treated Foundry Sand

Abstract

Reliability estimates of field hydraulic conductivity values of compacted bagasse ash treated foundry sand as landfill liners was under taken by incorporating a predictive model for hydraulic conductivity, which was developed from data obtained from laboratory results for specimens compacted at the energy levels of Standard Proctor (BSL), West African standard (WAS) and British standard heavy (BSH). These results were incorporated into a FORTRAN-based first-order reliability program to obtain reliability index values. variable factors such as water content relative to optimum, degree of saturation, bagasse ash content and percentage fines produced acceptable safety index value of 1.0 at the energy levels of BSL, WAS and BSH compactive effort and they were achieved at COV ranges of 10-100%. Observed trends indicate that the degree of saturation and bagasse ash content are greatly influenced by the COV and therefore must be strictly controlled in bagasse-foundry sand mixtures for use in covers and liners in waste containment facilities. While, recorded trend for water content relative to optimum  and percentage fines indicates that this variables do not significantly affect the reliability index of bagasse-foundry sand mixtures for use in covers and liners. Stochastic assessment of the model gave reliability index values in the range of 0.703-0.958, 0.935-1.188 and 1.165-1.416 at the compactive efforts of BSL, WAS, and BSH, respectively. Successful safety index values were recorded at WAS and BSH compactive efforts, therefore, only these two energy levels can be used to model the hydraulic conductivity behavior of bagasse ash treated foundry sand for landfill liners at COV ranges of 50-100% and 10-100%, respectively. Furthermore, using the F-distribution test at 95% level of significance, it was observed that the compactive effort has significant effect on the outcome of the recorded reliability index values from the ANOVA test. Therefore, care must be taken in ensuring that the compactive efforts that produced successful safety indices are carefully monitored during the construction of liner in waste containment facilities. The trend of the recorded results showed that reliability index (?) produced value of 1.0 which is considered adequate for serviceability limit state design.

Keywords: Compaction, Compactor weight, Hydraulic conductivity, Bagasse ash treated foundry sand  Reliability analysis, Reliability index, Soil composition, Soil liners