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1 <br /> <br /> <br />1 <br />1 <br />1 <br />1 <br />1 <br /> <br /> <br /> <br /> <br />1 <br /> <br /> <br />1 <br />1 <br />1 <br /> <br />Toe ditches were cut along the entire length of the downstream toe of the main embankment catch <br />line. <br />SRK as-built Drawing Nos. 14711-103 through 106 depict the final lines, grades and details of the <br />main embankment foundation. <br />2.2 Sputter Embankment Foundatlon <br />The sputter embankment foundation was located in cut. The cut in the upper reaches of both the <br />north and south abutment were relatively shallow and consisted mainly of stripping and shaping of <br />the areas. A drain blanket channel was excavated through the sputter embankment foundation to <br />connect the upper and lower impoundment invert grades. The drain blanket channel creates the <br />continuity for the upper impoundment and lower impoundment underdrain system, and the deeper <br />sputter embankment well sumps are also housed near the invert of the channel. The average width <br />of the channel invert after grading was approximately 60-ft wide. <br />The invert of the channel was raised above the plan grade due to sandy clays that were encountered <br />during the excavation. The sandy clays inhibited the vertical infiltration of surface water, which in <br />turn resulted in saturated materials above and around the sandy clayey layer. Three test holes were <br />excavated along the center line of the channel alignment to check for the depth of Saturation. The <br />test holes were dug to the elevation of the plan grade, i.e., 8,500 ft. The test holes indicated that <br />the saturated conditions continued below the depth of plan grade. Groundwater was observed to <br />be flowing from a lens of gravel in one of the test pits. Density tests of representative materials <br />were performed on three samples of the saturated sands and the clays, which indirated the sands <br />and clays were well consolidated. A decision was made to raise the invert grade of the sputter <br />embanlattent channel In addition, a 3-ft deep layer of selectively borrowed gravel was installed on <br />the invert of the channel excavation to allow ground water to travel unimpeded under the <br />foundation. A 4-in corrugated, perforated, HDPE pipe with a filter fabric sock was also installed <br />in the drainage layer. The drainage layer was dayughted into the alluvial gravels on both ends of <br />the sputter drain blanket embankment channel See SRK as-built Drawing No. 14711-1O5A for the <br />final grades of the sputter embankment foundation. S1ZIC as-built Drawing No. 14711-106 shows <br />a detail the sputter embanlm-ent subsurface underdrain. <br />The sputter embartlaetent excavation revealed the following geology. Very fine sands and gravels <br />were encountered in the upper reaches of the north abutment. Farther down the slope coarser <br />alluvium materials consisting of sands and gravels were encountered. These sahds and gravel <br />extended into the invert of the channel <br />5 <br />