C153644 Final Report - Laserfiche WebLink

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Figure 3 shows the cross section of the dam at the outlet pipe. Figure 4 shows the front elevation view of the embankment looking upstream from below the dam. The existing embankment material would be removed and stockpiled for use in the new embankment. If there is any unsuitable material, e.g. excess rocks or humus, the material would be wasted near the reservoir. Table 2 shows the estimated volume of material to be excavated. The dam site is extremely rocky. The foundation rock is apparently highly fractured. Installation of cutoff trench will be difficult both for excavation in the fractured rock and efficiency of the cutoff. Grouting of the foundation and abutments would normally be recommended but may be impractical because of the difficult access to the site. The next best recommendation is a core trench, but excavation of the foundation is required to determine if the trench can be excavated to an adequate depth. For purposes of this report, a 15 foot deep, 15 foot wide core trench is assumed most of the length of the embankment and upstream of the centerline. The availability of impermeable materials for the core of the dam is a major question. Early on, borrow areas must be tested to determine whether there is adequate permeable and impermeable material; also whether the US Forest Service will issue a permit to excavate the borrow. The design of the embankment included herein is approximate and included for cost estimating. Significant testing and design work will be needed to determine the best embankment design based on the availability of materials. The design assumes that there will be impervious material available but not in suitable quantities to construct the entire embankment, therefore the embankment design includes an impervious core with an pervious shell. If there is adequate impervious material to construct the entire embankment, it should be used. The embankment design includes an impervious core with 1.5H:1.OV slopes upstream and downstream. A pervious shell would be placed around the core with an upstream slope of 3.75A:1.OV and a downstream slope of 3.OH:1.OV. The slopes of the embankment are flatter than may normally be required because suitable filter materials are not expected to be available. The flatter slopes are included to add mass to the dam so that filters are not needed. Embankment material would be obtained from the stockpiled existing material and from a borrow area to be determined. The material would be placed in lifts and compacted to the appropriate density. Adequate testing will be required to monitor the compaction. Table 3 shows the estimated volume of material to be placed and compacted; 30$ additional material is assumed to allow for compaction. Big Battlement Dam 8