PROJC00465 - Laserfiche WebLink

Home Browse Search

. the pipe, Based on the video inspection, it appeared that the majority of the pipe was structurally sound, with the exception of the east end where the intake structure is located, It appears that the upper portion of the outlet pipe, immediately downstream of the intake structure had collapsed/failed, This pipe failure appears to be associated with the slope failure/slide that occurred along the upstream face of the embankment An area of apparent seepage was observed along the southern groin of the downstream face of the embankment in the natural soils situated uphill of the outlet We have not observed any seepage or standing water in this area during the last year, however the area is vegetated with wetland type grasses indicating a significant water source, Based on our review of the State Engineer's records, it appears that seepage had been previously observed in this area while the reservoir was holding water and the area was heavily vegetated with willows. It appears that the willows have been removed sometime between the State Engineer's inspection in 1996 and our first site visit in September of2000, . The spillway for the reservoir is situated approximately 125 feet southeast of the south end of the embankment The spillway appears to have been excavated into the natural soils and was approximately 18 feet in width. However, the client had constructed a stop log structure in the spillway, which reduces the effective width of the spillway to approximately 8 feet The spillway flows to the south-southwest away from dam and then discharges into a natural drainage way situated several hundred feet to the southwest of the dam. Field Investigations The field investigations for this project were conducted on October 10, 2000 and August 8, 2001. Five (5) test holes were drilled at the approximate locations shown on Figure #2 to explore the subsurface conditions in the upstream face of the embankment and in the proposed borrow area situated to the east of the existing spillway, A second field investigation was conducted on August 8, 200 I to evaluate the proposed borrow area located at the east end of the reservoir. Four test pits were excavated in this area and the approximate test pit locations are shown in Figure #2, The locations of the test holes and test pits were determined by a representative ofNWCC, Inc, in the field and the actual locations and elevations were determined by an instrument survey completed by Baker & Associates in August of 200 1. . The test holes were advanced through the overburden soils and bedrock with an all-terrain CME 55 drill rig utilizing 4-inch diameter continuous flight power augers and the test pits were excavated with a Case CK backhoe, The test holes and pits were logged in the field by an engineer from NWCC, Inc, Samples of the subsurface materials were taken with a 2-inch 1.0, spoon sampler, The sampler was driven into the various strata with a 140-pound hammer falling 30 inches, This test is similar to the standard penetration test described by ASTM Method 0-1586. Penetration values, when properly evaluated, indicate the relative density or consistency of the soils and bedrock, Large and small disturbed bulk samples were also obtained from the auger cuttings and sides of the test pit excavations, Depths at which the samples were taken are shown on the Logs of the Exploratory Test Holes and Test Pits in Figures #3 and #4. The Legend and Notes associated with the logs are shown in Figures #5 and #6, respectively, Slotted, 2-inch diameter PVC casing was also installed in the three test holes drilled in the embankment The temporary casings were installed so that the groundwater levels/phreatic surfaces under the embankment could be monitored in the future and to try to determine the failure surface of the failed soils, The bottom 15 feet of casing was slotted and the upper portion of the holes were cased with solid PVC. . Job Number: 00-4660 NWCC, Ine, Page 3