2010-02-11_REVISION - M2000158 (6)

Home Browse Search

3.03 EXCAVATION PROCEDURE 1. The Contractor shall take all precautions in conduct of work as may be necessary to avoid disturbance or damage to existing utilities and other structures. 2. The excavation equipment shall remain at least 20 feet away from overhead utilities. 3. The trench excavation shall be at least 2.5 feet wide. 4. The trench excavation shall start in the following order: 1. Pond D1 2. Pond D2 3. Pond C1 4. Pond C2 5. Pond B 6. Pond A Beginning location and direction of construction shall be coordinated with Construction Manager and approved by the Engineer. 5. Excavation of a lead-in trench is required if placement of the initial slurry is to be accomplished without the use of a clamshell. The lead-in trench shall commence far enough away from the cutoff wall and ramp down to the full depth of the cutoff wall at a slope of 1.5 horizontal to 1 vertical to avoid segregation of backfill particles. 6. The trench excavation shall be continuous to the depths indicated on the Plans or as directed by the Owner/Engineer. Actual depth of the wall will be determined based on visual observation of the trench cuttings. The wall shall be keyed into the dense base layer material at least 1 foot or as directed by the Owner/Engineer. 7. The entire depth of excavation shall be carried along the trench line. Prior to backfilling any portion, and before the excavator starts his next cut, the Contractor shall pass the excavating tool along the completed section of the trench excavation to confirm continuity. 8. The toe of the slope of the trench excavation shall not advance beyond the backfill slope by more than 200 feet. 9. The excavation shall be continuous from one end to the other, unless approved by the Owner/Engineer. If for some reason it becomes necessary for the slurry wall to be constructed in phased segments, some re-excavation of the previously constructed phase of the slurry wall will be necessary. This re-excavation shall consist of backfill removal and reconstruction of a minimum horizontal length of 10 feet of slurry wall over the entire depth of the wall, 10. The Contractor shall maintain trench stability to its full depth at all times. Sloughs, slides or any instability shall be re-excavated and/or repaired as approved by the Owner/Engineer. 11. Stockpiling. Material excavated from slurry trenches that is suitable for the backfill mixture may be stockpiled adjacent to the trench for subsequent processing. 12. Cobble and Boulder Removal. The Contractor shall excavate all cobbles and boulders as necessary along the slurry wall alignment and dispose of them at an on-site location -as directed by the Owner/Engineer. 3.04 SLURRY TRENCH BACKFILL A. Mixing 1. Mixing and blending shall be performed in such a manner as to produce the required backfill as specified in Paragraph 2.01F, Backfill. 2. The Contractor shall make every effort to cooperate with the Owner/Engineer in developing and enacting a mixing technique to satisfy the hydraulic conductivity criterion..