Laserfiche WebLink
4.0 DISCUSSION <br />This section documents construction delays, alignment changes, slurry and backfill quality, <br />and other construction issues. <br />4.1 Construction Delays <br />Excavation of the slurry wall began on March 14, 2013 and finished on June 14, 2013. <br />Excavation and backfill operations typically occurred Monday through Saturday with <br />Sunday as a day off for the crew. Slurry wall excavation did not occur March 18 through <br />March 22 as the Komatsu PC -8000 track hoe was down for repairs. Nor did construction <br />take place March 23 through April 1 or May 22 to May 28. <br />Construction was also delayed temporarily on occasion due to equipment maintenance, <br />logistics, and inclement weather. After delay periods, the slurry trench was cleaned out by <br />walking the excavator over the trench and removing approximately the upper two feet of <br />backfill in order to remove any settled or collapsed sand from the trench. In the period <br />from May 22 to May 28, limited backfill was placed daily to avoid significant sand <br />accumulation. <br />4.2 Slurry Wall Alignment <br />Prior to construction, adjustments were made to the slurry wall alignment due to the <br />presence of overhead power lines. The changes were made between approximate stations <br />24 +50 and 30+50 and 36 +50 and 40 +75 due to the presence of nearby overhead power <br />lines that paralleled the alignment. In addition, changes were made between approximate <br />stations 54 +00 and 58 +00 and 92 +10 and 94 +20 in order that the alignment could be <br />positioned such that the construction crossings were more perpendicular to the PSCO <br />power lines. These changes are documented on the as -built planset in Appendix A. <br />Much of the design slurry wall alignment included cross -cut corners when the cross cuts <br />would be away from the future reclamation slope (radii were used in the design to avoid <br />cross cuts towards the future reclamation slope). In some cases these cross cuts were <br />replaced with radii turns. This was the case near overhead power lines where the cross <br />cuts would have resulted in positioning the track hoe too close to the power lines. This <br />occurred at approximate stations 23 +90, 30 +60, 36 +00, 40+50, 53 +60, and 58 +60. Cross <br />cuts were also replaced by radii when changes in the alignment were relatively subtle such <br />as was the case at approximate Stations 72 +10, 92 +10, and 96 +30. <br />4.3 Slurry Ouality <br />Slurry viscosity (V), as measured using a Marsh funnel apparatus, and slurry unit weight <br />values, as measured using a mud balance, were maintained within the acceptable range (V <br />>40 seconds - Marsh, unit weight between 64 pounds per cubic foot (pcf) and 87 pcf. In a <br />few cases the slurry density was greater than 87 pcf in the trench. In these cases, the <br />contractor used the track hoe to bail slurry from the trench while replacing with fresh <br />- 4 - August 2013 <br />P:\23514 \133- 23514- I3003\Docs\ Reports\ Wattenberg _Construction_Report_2013.doc <br />