2006-04-12_REVISION - M1983067 - Laserfiche WebLink

Home Browse Search

• The site is in an alluvial valley setting. The natural Bound surface is flat with a terrace slope north to south splitting the site. Geotechnical test holes were drilled along the proposed slurry wall alignment prior to construction, which indicated bedrock is generally dipping to the east. Observed drill cuttings and soil samples, soil types, and depth to bedrock measurements were used as reference during construction. Test hole locations are shown on the map of the as-built sluny wall alignment and test hole locations (Figure 2), and geological exploration finding of each test hole and test pit aze presented on the summary logs (Figure 3a, 3b, and 4). Depths to bedrock and total trench depths observed during construction are illustrated on the as-built construction drawing (Plate 1). The natural site stratigraphy generally consists of three main units: 1) near surface sandy, silty clay and silty sand; 2) sand, gravel, and cobble alluvial deposits; and 3) claystone and shale bedrock. Locally, sandy clay "mud lenses" of thicknesses two to three feet are present in the alluvial deposits. Depth to bedrock is variable throughout the site. Bedrock depths ranged from 14 to 63 feet with an average depth of 32 feet. Trench depth worksheets are provided in Appendix B. In ' general, the depths to bedrock were Beater along the east side of the property and lesser on the west side of the property along the South Platte River. The slurry wall as-built dimensions are as follows: an average width of 3.5 feet, total trench depth 17 to 66 feet with an average value of approximately 35 feet, overall slurry wall length of 7,110 feet, and overall curtain area of approximately 248,900 square feet. The total area encompassed by the slurry wall is approximately 43 acres. CONSTRUCTION SUMMARY The typical slurry wall construction crew consisted of five to seven men managed by one superintendent who oversaw and coordinated construction activities. Motorized equipment included a Komatsu PC 1100 trackhoe excavator (shown on Figure 6), which excavated the trench through a water/bentonite slurry; a smaller trackhoe that provided initial soil-bentonite backfill mixing, trench backfilling, and slurry mixing pond construction; one Caterpillar dozer that provided final soil-bentonite backfill mixing, trench backfilling, and slurry mixing pond construction; a Caterpillar scraper which was used to move dirt to prepaze level Bound surfaces for the track hoe; two conical static mixer for preparing a bentonite slurry; two pumps used to recirculate slurry stored in the ponds and deliver slurry to the trench; and two standalone pneumatic trailers for on-site storage of bulk bentonite. A slurry pump/desanding unit was positioned along the side of the active trench to clean the trench bottom and reduce sands suspended in slurry. While construction was in process, the alignment of the slurry wall was modified to also encompass land directly north of Lafarge's Stagecoach property. The owner of the northern plot of land is Albert Frei & Sons. This changed the alignment of the slurry wall past station 51+30. For this reason, the slurry wall was constructed from station 0+00 to 51+30 in the counter-clockwise direction as planned, then extended northwest to station 62+60, and cut back in the southeast direction to tie-in at station 2+50 (also the ending point, station 71+10). Construction of the slurry wall continued past this point to create 35 feet of overlap to ensure the slurry walls met completely and did not have a gap between the two. After two attempts, the slurry wall was successfully overlapped. The slurry wall from station 0+00 through 2+50 was constructed before negotiations with Albert Frei & Sons. - 2 - Ianuary 2005 - Stagcmach Fiwl Conswction Repon.dm