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accomplish this, sufficient backfill shall be piled on the edge of the existing backfill to cause a slump and <br />sliding action on the face of the in-place backfill. The backfill shall not be dropped or deposited in any manner <br />that will cause segregation. An acceptable substitute for the initial placing of backfill by the use of a clamshell <br />bucket, shall be to begin excavation at a point outside of the limits of work which will provide a sufficient <br />distance for the backfill face to form, by pushing backfill into the trench, before the toe of the backfill reaches <br />the point where the cutoff is required. <br />3.09 TREATMENT FOR TOP OF CUTOFF TRENCH <br />Upon completion of backfill placement, and before drying of the backfill can occur, the cutoff trench shall be <br />capped in accordance with the details shown on the Drawings or as directed by the Engineer. <br />3.10 CLEAN-UP <br />After completion of the backfill and capping, all remaining excavated material and slurry shall be removed and <br />placed in thin lifts along the inside face of the reservoir and the surface shall be cleaned and leveled as directed <br />by the Engineer. Excess slurry shall be disposed of by spreading in this layers on adjacent areas designated by <br />the Engineer. No slurry shall be left in ponds, and all ponds shall be pumped dry and backfilled. <br />3.11 QUALITY CONTROL <br />The Contractor shall maintain his own quality control for the cutoff wall construction under the direction of a <br />qualified Engineer. Testing requirements are summarized in Table 1 and specified herein. <br />3.12 TRENCHING CONTINUITY AND KEY <br />The Contractor shall be responsible for demonstrating to the satisfaction of the Engineer that the trench is <br />continuous and keyed into the bedrock surface. Trench continuity shall be assured by the action of movement <br />of the trench excavation equipment such that the digging tools can be passed vertically from top to bottom of <br />the trench as well as moved horizontally along the axis of the trench without encountering unexcavated <br />material. Penetration of the bottom of the trench into the bedrock shall be demonstrated by observation of the <br />cuttings removed from the trench and the action of the excavating tools on the bedrock surface. <br />3.13 SLURRY AND BACKFILL <br />Testing requirements for slurry and backfill are as follows (and are outlined in Table 1): <br />A. Materials <br />Bentonite: Certification of compliance with the specifications shall be obtained from the <br />material manufacturer. <br />2. Backfill Mix: Backfill material shall be tested prior to placement in the trench by conducting <br />tests to determine slump and gradation. Testing frequency will be as directed by the <br />Engineer with a minimum of one series of tests per 200 cubic yards of backfill material <br />prepared for introduction in the trench or as specified in Table 1. <br />B. Slurry Introduced in the Trench <br />A complete series of tests shall be conducted on slurry from the pond containing slurry ready for <br />introduction in the trench at least once per shift or each time a pond is prepared or as specified in <br />Table 1. The tests shall include: <br />pH of the slurry, <br />Unit weight of the slurry, <br />Filtration loss of the slurry, and <br />Viscosity of the slurry. <br />4/08 Section 02168 - Page 4 of 5