2006-02-02_GENERAL DOCUMENTS - M1999120

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previously recorded, trench cleaning will be done prior to additional backfill placement. If the unit weight of the slurry in the trench exceeds the specified limits or becomes unworkable, the heavy slurry shall be removed from the trench. 3.08 BACKFILL MIXING Material from borrow shall be mixed and blended in mechanical blenders or by windrowing, disk harrowing, bulldozing, blading or by other approved methods. Mixing and blending shall be performed in such a manner as to produce the required gradation of backfill. The backfill material shall be thoroughly mixed into a homogeneous mass, free from large lumps or pockets of fines or sands. Occasional lumps of up to 6" in their largest dimension will be permitted. Just prior to placing, the backfill material shall have a slump of 2" to 6". To this end, the material shall be sluiced with slurry during blending operations. Sluicing with water will not be permitted. 3.09 BACKFILL PLACEMENT The backfill shall be placed continuously from the beginning of the trench, in the direction of the excavation, to the end of the trench. The toe of the slope of the trench excavation shall not be less than 10' following the toe of the excavation, or as required to permit inspection and measurement. Placing operations shall proceed in such a fashion that the surface of the backfill below the slurry wall follow a reasonably smooth grade and shall not have hollows, which may trap pockets of slurry during subsequent backfilling. Free dropping of backfill material through the slurry will not be permitted. Initial backfill shall be placed by excavating a "lead-in trench" within the slurry wall alignment. The "lead-in trench" will be excavated to a slope of 1:1. Initial backfill will be placed in such a manner that the backfill enters the trench sliding down the lead-in slope until the backfill rises above the surface of the slurry trench. Additional backfill may then be placed in such a manner that the backfill enters the trench by sliding down the forward face of the previously placed backfill. To accomplish this, sufficient backfill shall be piled on the edge of the existing backfill to cause a slump and sliding action on the face of the in-place backfill. The backfill shall not be dropped or deposited in any manner that will cause segregation. 3.10 TREATMENT FOR TOP OF CUTOFF TRENCH Upon completion of backfill placement, and before drying of the backfill can occur, the cutofif trench shall be capped with a 1' thick (minimum) clay cap. Clay for capping will be borrowed from the existing overburden stockpiles. 3.11 CLEAN-UP After completion of the backfill and capping, all remaining excavated material and slurry shall be spread out over the site, and blended into the upper soil. The Owner shall be responsible for all other reclamation activities, including final regarding of the site (including temporary construction easements), and repairing existing structures such as ditches and fences. 3.12 QUALITY CONTROL The Contractor shall maintain its own quality control for the cutoff wall construction. Quality control shall be performed in accordance with the approved Quality Control Plan submitted by the Contractor. Laboratory permeability testing of the backfill shall be performed by a third party as approved by the Design Professional and Owner. Testing requirements are summarized on Table 1 as specified herein. 3.13 TRENCHING CONTINUITY AND KEY The Contractor shall demonstrate that the trench is continuous and keyed the minimum specified depth into the underlying aquiclude. Trench continuity shall be assured by the action of movement of the trench excavation equipment such that the digging tools can be passed vertically from top to bottom of the trench, as well as moved horizontally along the axis of the trench without encountering unexcavated material. Penetration of the bottom of the trench into the aquiclude shall be demonstrated by observation of the cuttings removed from the Section 02168 -Page 4 of 5 02/06