Laserfiche WebLink
Site Conditions <br />The subject slide is located approximately 300 to 500 feet east of the Train Loadout Facility at the <br />Twentymile Mine in Routt County, Colorado. A site plan showing existing features and approximate <br />locations of the slope failure is presented in Figure #2. <br />The slide (slope failure) is located between the conveyor belt and the railroad tracks. The subject failure <br />ranges from approximately 100 to 120 feet in width at the uphill portion of the slope (immediately north of <br />conveyor) to approximately 230 feet in width at the toe of the failure (immediately south of train tracks). <br />The head scarp for the failure has propagated uphill to the north edge of the conveyor exposing several of <br />the concrete foundation/supports and has prevented the use of the access road situated north of the <br />conveyor. Based on recent site observations, the head scarp does not appear to have propagated <br />significantly uphill between August and December 2011. It should be noted that groundwater seepage was <br />observed flowing from the toe of the slope failure and along the railroad tracks at the time of our initial site <br />visit in July 2011. <br />The failed slope consists of an embankment fill constructed for the operation of the conveyor and access <br />road. NWCC understands that fill materials have been placed several times along the northern edge of the <br />conveyor in the slope failure area to keep the access road operational. <br />The topography o0f the slide area is variable due to previous site grading and slope movement. The site <br />slopes moderately to steeply down to the north on the order of 15 to 70 percent. Slopes situated to the east <br />and west of the slide area are more consistent and generally slope down to the north on the order of 25 to <br />50 percent. A maximum elevation difference of approximately 30 feet exists across the site between the <br />railroad tracks and the conveyor. <br />The majority of the site is relatively free of vegetation due to disturbance and fill placement. Vegetation in <br />adjacent, non - disturbed areas consists of grasses and weeds. <br />Field Investigation <br />The field investigation was conducted on August 12 and 15, 2011. Six (6) test holes were advanced across <br />the site at the approximate locations shown in Figure #2. The test holes were advanced through the existing <br />fill materials, overburden soils and into the underlying bedrock materials with 4 -inch diameter continuous <br />flight augers using a CME 55 truck - mounted drill rig. <br />Samples of the subsurface materials were taken with a 2 -inch I.D. California liner sampler. The sampler <br />was driven into the various strata with blows from a 140 -pound hammer falling 30 inches. This test is <br />similar to the standard penetration test described by ASTM Method D 153 -86. Penetration resistance <br />T-h T.r „n,F.ar 11-8970 <br />N.TWnr, In Page 2 <br />