LINEAR OPTIMIZATION OF SOIL MIXES IN THE DESIGN OF VERTICAL CUT-OFF WALLS

Abstract

In order to prevent the contamination of surrounding groundwater in a landfill, cut-off walls
were recommended. Cut-off walls are walls utilized when there is a need to restrict horizontal movement of
liquids. Currently, the factors in designing cut-off walls are effective permeability, and relatively inexpensive
materials in containing contaminants. It was suggested to provide a mix of 96% soil and 4% bentonite in the
design of cut-off walls, but bentonite is relatively expensive, thus the viability of fly ash as a replacement for
bentonite was considered. Soil mixtures were proposed and rigorous laboratory tests was performed to
determine the individual properties. Tests such as specific gravity tests, Atterberg limit tests (liquid limit,
plastic limit and plasticity index), emax and emin test/relative density tests, particle size analyses, microscopic
characterizations, elemental composition tests and permeability tests were performed to garner data, and were
utilized for the model. A linear optimization model was generated to achieve the least cost with the minimum
required permeability. The minimum permeability requirement for the cut-off wall was achieved by providing
various mixtures for soil-bentonite-fly ash.