Engineering geological evaluation of Mfensi and Afari clay deposits for liner applications in municipal solid waste containment systems

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Mfensi and Afari clay deposits in the Ashanti region of Ghana, have been the subject of considerable research works mainly for pottery, brick and tile, pozzolana, refractory productions, etc, but very little is known about their application as liner materials. This study therefore sought to evaluate the suitability of the two clay deposits as liner materials in municipal waste containment systems. Samples were collected from the sites and subjected to physical, chemical, physico-chemical, mineralogical, geotechnical as well as thermal analyses. Results of the study reveal that; physically, both clays were soft and had high water contents. Afari clay was yellowish in colour while Mfensi clay was greenish-grey in colour. The chemical compositions of the clays were analogous although their concentrations varied. The oxides of silicon, aluminum and iron together constitute about 90% and 80% in Mfensi and Afari clay respectively. The mineralogical compositions of both clays were similar and made up of quartz, kaolinite and magnetite. The cation exchange capacities of the clays were 32.33 meq/100g for Afari clay and 7.79 meq/100g for Mfensi clay. The clays were fine grained, with fines contents of approximately 64% and 88% for Afari and Mfensi clays respectively. Texturally, both clays classify as clay loam. The Atterberg limit tests gave the liquid limits and plasticity indices of both clays to be 64.78% and 40.52% for Afari clay and 42.85% and 22.43% for Mfensi clay respectively. The unconfined compressive strength of the Afari clay was 244.53KPa and that of Mfensi clay was 331.73KPa. The hydraulic conductivities of the clays were found to be of the order ×〖 10〗^(-7) cm/s. The average thermal conductivities of the clays were 0.025W/moC for Afari clay and 0.215W/moC for Mfensi clay. The use of leachate led to an increase in the plasticity indices and liquid limits of both clays with a reduction in the plastic limits. Reductions in the permeability’s of both clays were also observed when permeated with leachate. From the modeling, Afari clay had a higher flow rate and a lower breakthrough time relative to Mfensi clay. It is concluded that, Mfensi clay has a better anti-leakage behavior, higher breakthrough time and lower flow rate relative to Afari clay. Based on parametric analyses from the simulation with varying leachate head, leachate density and liner thickness, it was found that, the breakthrough times of both clays did not change when varying the leachate head while the flow rate changed with varying leachate head. Also, the breakthrough times and flow rates of the clays changed with varying liner thickness. Finally, the variation in leachate density resulted to a change in the breakthrough times for both clays and had no effect on the flow rates. From the overall study, the clays generally passed the requirement for use as liner materials in municipal solid waste landfills and hence they could be used for liner applications
A Thesis Submitted to the Department of Geological Engineering, Kwame Nkrumah University of Science and Technology in partial fulfillment of the requirements for the degree of Master of Philosophy (GEOLOGICAL ENGINEERING) College of Engineering Department of Geological Engineering.