2015-12-03_GENERAL DOCUMENTS - M1974070 (5)

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