2006-03-17_REVISION - M1982015 - Laserfiche WebLink

Home Browse Search

Supplemental Geotechnical Engineering Report Proposed Slurry Cut-off Walls @ St. Vrain Development Weld County, Colorado Terracon Project No. 25045300 Terracon Adjacent to the proposed slurry wall- Boring Nos. 9,10, 13, 23, 24, 30, 31, 33, 34, 35, 39, and 40 through 45 (Terracon Project No. 25045300). Within portions of the overall St. Vrain Development- Boring Nos. 28- 31 and 33- 40 (Terracon Project No. 25045122). • Embankment Fill (poorly graded sand or sand with gravel): Adjacent fo the proposed slurry wall- Boring Nos. 32, 35, 36, 37, 38 and Packer 1 through Packer 4. Slurry Wall Alignment Considerations; Ahydro-geologist should be consulted to evaluate the potential impacts of the impermeable zone which will be created by the slurry walls in relation to existing regional groundwater gradients/flows. We anticipate that some "mounding" effects (trapping/buildup of groundwater flow) could occur on the northern boundary of the lakes. Interceptor drains could be considered as a means of diverting the regional groundwater around the slurry wall lakes to the natural drainage basin to the south (St. Vrain River). At a minimum, consideration should be given to minimizing sharply curving alignments along the northern portion of the lake which could "trap" or "mound" groundwater. A slurry wall or other relatively impermeable barrier will be required between the swim lake and the main lakes to maintain the differential elevations of the lakes, the clarity of the water in the swim area, and the integrity of the embankments between the bodies of water. We understand that asheet-pile wall is also being considered as a separator and means for constructing a pedestrian/vehicular path between the main peninsula and the island to the south of the swim lake. Sheet piling is discussed in the following section of this report. Based on current project information, a preliminary slurry wall alignment has been generated and provided at the end of this report (Figure 3). Embankment, Island, Peninsula, and Swim Beach Construction Considerations; Soil embankments/slopes will be required on the lake side of the slurry wall in order to create "buildable" land and resist lateral earth pressures and the hydrostatic forces from the relatively high groundwater conditions at the site which will likely be exacerbated by the installation of the slurry walls and to support slurry walls located between separate lake features. Once preliminary design plans for the slurry walls are made available, detailed analyses for lateral earth pressures and hydrostatic forces should be generated to assess global stability of the slurry cut-off walls. For preliminary planning purposes, interior slopes which will be supporting the slurry walls should be designed such that they do not exceed approximately 3 or 4 :1 (horizontal :vertical). Flatter slopes will likely be desirable in the swim beach areas to facilitate access/foot traffic info the water. As previously outlined, a 11