Laserfiche WebLink
<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />t <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />The investigation showed the valley floor to be covered by about 20 <br />feet of alluvial gravel and sand described in the geologic mapping. <br />Borehole RC-C2 was vertical and showed the bedrock to be sound, hard <br />medium grained, pink granite, with occasional amphibolite inclusions. <br />The core was moderately jointed to locally highly jointed. Water <br />losses from pressure testing were uniformly low. Borehole RC-Cl on the <br />left abutment was angled 700 into the slope and detected medium grained <br />pink granite at a depth of 2.5 feet. The rock, however, was highly <br />fractured with some weathered joints to a depth of about 20 feet. The <br />limited water pressure testing achieved in the borehole showed the <br />upper 15 feet to be very permeable and below that depth fairly tight. <br />The seismic refraction line on the left abutment showed the talus slope <br />and weathered in place rock below the borehole to be as thick as 35 to <br />40 feet. Hole RC-C3 on the right abutment was also angled 700 into the <br />slope and penetrated 31 feet of highly weathered and fractured rock. <br />Sound, fine grained, pink granite was logged almost exclusively below <br />that depth except for an occasional amphibolite inclusion or pegmatite <br />vein. The core recovered, however was highly fractured to fragmented, <br />but was sound with no sign of weathering. It was not possible to con- <br />duct water pressure tests in the hole. The seismic refraction work <br />coincided with the boreholes and showed the top of sound rock to be as <br />deep as 35 to 40 feet over the entire abutment. <br /> <br />The seismic refraction lines at Site A upstream showed the top of rock <br />in the alluvial valley floor to be about 20 feet deep. The top of <br />sound rock on the left abutment, however, ranged to a depth of 50 <br />feet. The seismic section on the spillway alignment showed the depth <br />to the top of sound rock to be in the 25 to 35 foot range. <br /> <br />Appendix C-1 contains details of the subsurface investigation program <br />including drill logs and results of laboratory testing. <br /> <br />2. Construction Materials - Preliminary evaluations <br />Rock Creek site would be suitable for an RCC gravity dam. <br />struction materials investigation, therefore, centered on <br /> <br />indicated the <br />The con- <br />locating a <br /> <br />3 - 10 <br /> <br />6819W/502OW <br />