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------------------- -------------- - --- - KLEINFELDER 6.2.2 Barrier Layer The low permeability barrier layer shall be constructed on a foundation layer that has been compacted to provide a uniform firm surface. The actual manner in which the barrier layer shall be constructed will likely be dependent on whether the county or an outside contractor performs this work. For a large contractor, having large compaction equipment capable of achieving 95% compaction on lifts exceeding 12 inches in loose thickness, the most efficient approach will likely be to place approximately 12 inches of borrow material loosely upon the compacted foundation layer followed by the specified amount of Ione clay. The combined loose thickness of the borrow materials and Ione clay may be on the order of 14 to 16 inches, which is then completely mixed in one operation by large rotor- tilling equipment, such as a Bros or Rago cross shaft mixers or equivalent. If difficulty in meeting the required density is encountered in the field, it may be necessary to decrease lift thickness. The mixing equipment must have the ability to add water to the mixing chamber so that a uniform soil/clay/water mixture is obtained. Mixing operations should comply with Section 24 of Caltrans Standard Specifications regarding particle size. -In order to achieve the maximum particle size requirement, which is a minimum of 60 percent passing the No. 4 sieve size, multiple passes may be required. As an alternative, borrow materials, and Ione clay can be mixed by county personnel and i equipment using small rotor-tiller equipment on grade or on "a mixing table". By this method, the maximum loose thickness should be reduced to 6 to 8 inches, or to the capacity of the rotor-tiller equipment. Due to the uneven nature of Ione clay, belly or end dumping followed by spreading using a blade in the field is the normal method of spreading. Since this method of spreading can f produce variations in the percent of Ione clay added, say from 17 to 23 percent, it is L important that other factors necessary to determine clay quantity be conservative in nature. For this reason, we recommend that a maximum laboratory dry density of 120 pounds per cubic foot (pcf) be considered for the Ione clay and native soil mixture. This assumption is based on 3 compaction curves performed in our laboratory, with 15 percent Ione clay added to the native soil. On previous projects, a specified number of trucks were unloaded within a designated area. The number of trucks was dependent on the amount of clay ( carried by each truck and the moisture content of Ione clay, since the specified 20 percent Ione clay is based on dry weight. Our experience has been that most semi truck and trailer rigs carry approximately 25 tons of moist Ione clay, and Ione clay has an average moisture L CR9-42 Page 19 of 28 Copyright 1991 Kleinfelder, Inc. AIN