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Lined Pit Guide 9 September 2000 <br />Supplementary water, if required, shall be added to the material by sprinkling on the earth fill, <br />and each layer of earth fill shall be conditioned by disking or other approved methods so that the <br />water is distributed uniformly throughout the layer. <br />Mechanical mixing to distribute water evenly in the soil is particularly important for highly plastic soils <br />that form large clods. <br />Compactive Energy <br />The energy of compaction is an important variable controlling the engineering properties of soil liner <br />materials. Increasing the energy of compaction increases the dry unit weight of the soil, decreases the <br />optimum moisture content, and reduces permeability. The compactive energy delivered to soil depends <br />on the weight of the compaction equipment, the number of equipment passes, and the thickness of the <br />loose lift of soil being compacted. The best combination of these factors to use when compacting low <br />permeability soil liners depends on the targeted maximum permeability, equipment availability, <br />economic feasibility, experience on similar projects, and test results with the site specific soils. For a <br />typical soil liner fill composed of weathered shale, the specifications may call for a minimum of 5 <br />passes over a maximum 9 inch thick loose lift with a 40,000 pound or greater compactor. <br />Size of Clods <br />Highly plastic soils almost always form large clods. For soils that form clods, they must be remolded <br />into a homogeneous mass that is free of large inter-clod pores if low permeability is to be achieved. As <br />discussed previously, when the soil is compacted wet of optimum that clods are sufficiently soft to be <br />easily remolded. If dry clods must be reduced in size prior to compaction, which may be the case when <br />using ripped shale as a liner material, a road reclaimer or other similar equipment may be used to <br />pulverize the material. <br />Bonding of lifts <br />Proper bonding of lifts is important in achieving low permeability in soil liners. Poorly bonded lifts <br />result in high horizontal permeability at lift interfaces. Water moving through a liner will spread <br />laterally along these interfaces increasing the likelihood of leaking at any permeable zones that may be <br />present in the underlying lift. To bond lifts together, the surface of the previously compacted lift should <br />be roughened so that the new lift can blend into the surface. The design should address lift bonding by <br />specification of discing lift surfaces or using compactors with tamping feet long enough to fully <br />penetrate the specified loose lift thickness. <br />Keyway <br />The wedge of soil liner fill that will form the impermeable barrier around the perimeter of a reservoir <br />must be keyed into a competent impermeable strata at the floor of the pit. The keyway is installed by