C153604 Feasibility Study - Laserfiche WebLink

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. . Seepage from saturated portions of the embankment discharging Into the outlet conduits can cause a condition known as piping, whereby fine grained soils from the dam embankment are transported from the fill, creating a void which allows greater flows and, subsequently, more soil loss, This condition can ultimately lead to a partial or complete failure of the embankment. It is our opinion that over the years a seepage path has developed along the embankment interface at the top of the conduit, and is evidenced by extensive seepage from cracks within the conduit and at the downstream headwall structure, . . Monitoring and observation holes drilled into the Dam No.4 embankment adjacent to the outlet conduit have revealed a lens of sand and gravel in the embankment fill which is contributing to the seepage evident at the downstream toe area of the dam. Because of the potential for piping, we believe the sand and gravel layer, which may have been placed as backfill for the outlet conduit, could pose a serious threat to the long-term integrity of the dam, . . Without the rehabilitation of the outlet works, the concrete in the conduit will continue to deteriorate and seepage flows can be expected to increase along with the accompanying increase in piping of the embankment materials, The structure faces an increasing probability of catastrophic failure or severe reservoir storage restriction by the State Engineer. . Geotechnical Invest illation Extensive geotechnicaf'investigations have been performed with respect to major structural rehabilitation of the Julesburg Dam Nos, 2 and 3. The investigations included exploratory test holes in the embankment fills and foundation materials; soil sampling and classification; laboratory testing including shear tests, grain size analyses and triaxial tests; installation of piezometers; and stability analyses. The rehabilitation of the two dams consisted of installation of toe drains and a filter blanket, stabilized by the placement of an earth-fill berm along the toe of the dams. . . Geotechnical reports were prepared for Dam Nos, 2 and 3 by Chen and Asso<::iates, which describe the investigations and analyses performed and the results obtained. The various geotechnical reports are dated August 3, 1978; September 11, 1986; October 21, 1986; August 27, 1987; November 20, 1987; and April 4, 1988. Based upon the recommendations of the reports, the repair measures were designed by Chen and Wheeler, reviewed and approved by the State Engineer's Office, and constructed, . 14 .