HX Detention Dam Maintenance Bureau of Land Management
HX Detention Dam suddenly breached sometime in the summer of 2014 which presents hazards to those who use the crest as a road. The contract involves making geotechnical investigations of the current condition of the breached embankment specifically as to the extent of damage from which excavation is to be performed to seek competent foundation material which is to be confirmed by compaction tests. Since the breached embankment material washed away, geotechnical investigations are required in order to find acceptable borrow area sources to match embankment materials via classifying the soil materials under the Unified Soil Classification System before rebuilding the embankment and the eroded impoundment just upstream and the area just downstream can be undertaken.
SCOPE OF WORK:
- Remove and neatly stockpile barbed wire fence on embankment
- Clear and grub 0.5 acres in plan view around the breached area, and backfill and compact within 50 feet outside the toe lines of the dam’s embankments and to the cut lines of the laid-back slope.
- Excavate loose soil in the invert of the breach to competent soil for a foundation, and stockpile for use.
- Lay back the embankment’s steep slopes to competent soil at safer slopes, and stockpile for use.
- Find borrow areas for acceptable earthfill for a total placement of 25,000 Cu.Yds.
- Cut a keyway in invert and up the laid-back slopes to a final location in accordance with the Specifications with field approval by the COR.
- Prepare foundation for rebuilding embankment.
- For the embankment, place earthfill in lifts, and properly compact starting from the approved prepared foundation up to specified finish surface. Earthfill shall be used wherever gravel fill is shown in the original design drawings.
- For the upstream and downstream eroded areas, place earthfill in lifts from the existing foundation starting from the current invert to the approximate limits shown in the Specifications.