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Brighton Water Storage Project , <br /> Slope Stability Calculations _ <br />• ~ <br /> ~ Adams County, Colorado <br />' Machette (Geologic Map of the Greater Denver Area; Front Range Urban Corridor, U.S. <br /> Geological Survey, Map I-856-H, dated 1979). The sands and gravels are underlain by bedrock <br />' consisting of claystone with Iocal sandstone beds and lenses. These sands and gravels apparently <br />w <br />re mined t <br />r <br />f <br />th <br />i <br />ti <br />Th <br />h <br />ll <br />k <br />t <br />i <br />l <br />i <br />d t <br />b <br />b <br />d <br />t <br />t <br /> e <br />o <br />o <br />m <br />e ex <br />s <br />ng quarry. <br />e s <br />a <br />ow <br />e <br />roc <br />ma <br />er <br />a <br />s are <br />n <br />erpre <br />e <br />e <br />o <br /> „Denver Formation deposits. GROUND'S test holes penetrated from about 26 to 43 feet of sands <br />' and gravels before encountering bedrock. Groundwater was encountered at depths from about 17 <br /> to 26 feet below existing grades outside the quarry. Water levels can fluctuate; however, in <br />' response to annual and longer-term cycles of precipitation,'irrigation, surface drainage and other <br /> factors.' ' <br />' Sands and Gravels ranged from gravelly sand to sub-equal proportions of sand and gravel, with <br /> local minor silt fractions. They were fine to coarse grained, slightly moist to saturated, non- <br />' plastic, medium dense to dense, and light brown in color. - - , <br />' - Claystone Bedrock was clean to slightly sandy, moist, highly plastic, hard to very hard with the <br />li <br />i <br />l <br />i <br />l <br />H <br />d <br />f <br /> rau <br />y, and dark gray to dark gray-brown <br />n co <br />or. <br />y <br />c <br />upper few <br />eet h <br />ghly weathered local <br /> conductivity testing of a remolded sample of the claystone indicated a hydraulic conductivity . <br /> value of approximately 1.2 x 10',cm/s. Our tests indicated that the in-place claystones were not . <br /> -saturated, except perhaps within a few feet of the top-of-bedrock surface. _ <br />' ' i <br />i <br />l <br /> c, very <br />Sandstone Bedrock was silty, fine to medium grained, moist, non-plastic to slight <br />y p <br />ast <br />' hard, and gray in color. <br /> Slope Stability Analyses <br />Slope stability analyses were performed on a-representative cross section through the proposed <br />reservoir wall using generalized subsurface profiles based on the materials as encountered in the <br />test holes. Project slopes in three stages of construction-were modeled: the excavation back cut, <br />prior to placement of the liner, the finished liner slope prior to placement of the `miscellaneous <br />fill,' and the final proposed slope configuration. The back cut and liner slopes were considered to <br />be temporary slope conditions which would be, required to stand for only relatively limited <br />periods of time. Two subsurface profiles were considered for each,of these construction stages, <br />a) relatively shallow bedrock as was encountered in the northeastern portion of the site -modeled <br />with the top-of-bedrock surface at a depth of 30 feet,below top=of-slope, and b) relatively deep <br />bedrock -modeled with the top-of-bedrock surface at a depth of 41 feet below top-of-slope. <br />lob No. 02-0065 <br />Ground Engineering Consultants, Inc. ~ ', Page 4 <br /> <br />