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/ • • <br />Sylvester Gulch Facilities Area Construction <br />Slope Stability Concerns <br />Landslide - Main Access Road <br />A landslide commenced on July 4th between approximately stations <br />62+00 and 66+00 on the SGFA main access road. The road embankment <br />had been partially constructed. A maximum of approximately 30 feet <br />of fill had been placed on the slope west of the Sylvester Gulch <br />channel. The toe of the embankment was approximately five feet <br />from the channel in places. The highest pull apart crack measured <br />approximately five feet across with approximately seven feet of <br />vertical offset. The road is impassible. <br />Eric Mende of Mountain Coal's environmental staff has been <br />compiling daily visual measurements of crack growth. Eric's data <br />shows that the rate of downslope movement has slowed, but as of our <br />visit, was continuing at approximately 1 foot per day. Some <br />transe cracking is apparent on the slope between the toe of the <br />fill nd the creek. No significant compression ridge was evident. <br />No d's ortion is apparent on the opposite eastern side of the <br />Sylvester Gulch stream channel. The stream channel adjacent to the <br />down gradient third of the failed embankment appears to have been <br />reduced to approximately one foot in depth and width with grassed <br />sides and bottom. Above the landslide to the south the undisturbed <br />channel is approximately five feet wide and three feet deep with <br />bare sides and bottom. My conclusion is that the failure plane of <br />the slope failure exists within the foundation slope beneath the <br />road fill. The elevation of the failure plane appears to coincide <br />closely with the elevation of the stream channel. Rather than form <br />a compressional mound, the failed bedrock appears to be overriding <br />the alluvium, obliterating the original stream channel. <br />Mountain Coal Company (MCC) will have to identify the elevation and <br />orientation of the failure plane. Sufficiently precise <br />monumentation will need to be installed to define the rate and <br />direction of movement. Test pits and augered test holes should <br />verify the location and orientation of the failure plane. Sampling <br />and lab analyses should provide the strength parameters for the <br />failed soil material. Experience has now proven that the <br />Division's suspicion that lab analysis of collected rock and soil <br />specimens was not the appropriate methodology by which to determine <br />effective slope mass properties. Now a very contemporaneous <br />opportunity has presented itself for the back calculation of <br />appropriate slope bulk strength properties. These strength <br />parameters, in turn, should be used for the rehabilitated slope <br />designs. <br />Once the above information is obtained, MCC will then need to <br />develop a remedial treatment for the failed mass. If the failed <br />mass cannot be rehabilitated to support the access road, it will <br />