PROJ00137 - Laserfiche WebLink

Home Browse Search

I I 1 I I I I I I I I I I 1 I I I I I =============================================================================== Table V;3; Twin Lakes Dam Rehabilitation Alternative No.3 o Replace outlet works by pipe jacking new conduit through embankment and plugging existing conduit. Construct new inlet and outlet structures. o Raise dam crest from elevation 9300 to 9308 to provide storage capacity of approximately 460 acre-feet and freeboard during fl oodi ng. o Construct RCC overflow di ke spi 11 way across exi sti ng spi 11 way channel with a crest elevation of 9303. o Pl ace fi lter bl anket on downstream face and foundati on surface to control and collect seepage. o Install toe drain system to collect and discharge seepage. o Flatten downstream slope to 2.5:1 with sand and gravel pit run material. o Remove existing riprap to raise dam. o Provide 3:1 upstream slope using sand and gravel pit run material: o Place bedding layer and riprap on upstream slope. Outlet Works Option Plug existing conduit and construct siphon over crest of dam. Spi 11 way Opti on Construct earth dike across existing spillway channel and provide a rock cut spillway on the right abutment of the dam. =============================================================================== The degree of techni cal confi dence wi th regard to embankment stabil i ty for this alternative is moderate. Collecting and controlling the seepage passing through the dam would help to control the phreatic surface and enhance embankment stabi 1 i ty. However, the pervi ous nature of the embankment materi al s reveal ed duri ng drill i ng i ndi cates that pi ezometri c 1 evel sin the dam will remain relatively high if seepage reduction measures are not employed. The technical confidence existing embankment is low. associated with The behavi or of jacking a conduit through the materials surrounding the pipe as -67-