Laserfiche WebLink
<br />e <br /> <br />e <br /> <br /> <br />Figure 4 shows the cross section of the dam at the outlet tunnel. <br />Figure 5 shows the front elevation view of the embankment looking <br />upstream from below the dam. <br /> <br />The surface of the existing embankment and the area below the toe <br />of the existing embankment will be removed and wasted because it <br />contains humus and rocks. The material to raise the embankment <br />will be placed on the downstream slope. A core trench is assumed <br />at the downstream toe of the existing embankment that is 20 foot <br />deep and 20 feet wide. Though the core trench is downstream of the <br />crest, it is included to impede foundation water seepage. <br /> <br />The volume of material to be placed in order to enlarge the dam was <br />quantified by estimating the volume of the existing embankment, <br />shown in Table 2. The volume of the enlarged embankment is shown <br />in Table 3. The difference between the existing and enlarged <br />embankment is estimated to be the amount of material to be placed <br />to raise the dam, plus 30% for compaction loss. <br /> <br />Embankment material is assumed to be obtained from a borrow area in <br />the reservoir basin. The material is expected to be impervious <br />material so that the entire downstream slope is homogeneous core <br />material; if pervious material is available the design may be <br />changed to include a pervious shell on the downstream slope. The <br />material would be placed in lifts and compacted to 95% Standard <br />Proctor. Adequate testing will be required to monitor the <br />compaction. <br /> <br />A toe drain is included to control seepage through the embankment <br />and to address the groin seepage. The drain would probably be a <br />sand filter (ASTM C-33 sand) with a slotted drain pipe to convey <br />water out of the filter. The drain is estimated to be 5 feet deep, <br />2 feet wide and about 200 feet long. <br /> <br />No other drainage system is included in this preliminary design <br />because the existing dam is apparently in good condition without <br />serious seepage. Also, the enlargement includes the placement of <br />a large mass of material on the downstream slope with a thick 25 <br />foot crest width. If drainage filter material is readily available <br />a chimney filter at the contact between the existing downstream <br />slope and the new material should be considered. <br /> <br />Rock for rip rap does not appear to be available immediately around <br />the reservoir and must be hauled from a site assumed to be within <br />5 miles. The area to be rip rap'd would be about 60 feet wide and <br />600 feet long. <br /> <br />Red Mesa Dam <br /> <br />8 <br />