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REP17203
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REP17203
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Entry Properties
Last modified
8/24/2016 11:46:17 PM
Creation date
11/27/2007 2:04:20 AM
Metadata
Fields
Template:
DRMS Permit Index
Permit No
C1981019
IBM Index Class Name
Report
Doc Date
7/7/1995
Doc Name
PN C-81-019 COLOWYO COAL CO LP REQUEST FOR TR-34 WEST PIT POND MAINTENANCE
From
COLOWYO COAL CO LP
To
DMG
Permit Index Doc Type
Waste Pile/Fill Report
Media Type
D
Archive
No
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the primary factor which Inltlated the slide was seepage water from the south. The <br />geometry end pond water avallablllty were In-place for a slgnlflcant period of time, only <br />when eeepags developed during the spring was the slide triggered. <br />The elide ooeurred In a area with an unfavorable bedrock orisntatlon. 9eepe to <br />the area were noted previously end several other slides haw occurred in the adJacent <br />valleys, Prior to the slide we did not observe any signs of Imminent Instability at the slide <br />location In our previous site viska. The development of a slide in this Brea can be due <br />to several factors and small variations in the slope geometry, bedrock dip, dip direction, <br />or seepage conditions can slgnlflcantly change condltlons. The undulations In the <br />bedrock surface make It difficult to prodlct on a local balls the slopes or elope directions <br />which are potentially least stable, although north facing alopee appear most vulnerable. <br />In our opinion, the topsoil stockpile was not constructed in a location which could have <br />reasonably been .predicted as unstable. It Is possible that a landslide could have <br />occurred at this location without the presence of the topsoil stockpile. <br />Based upon our observations, we believe earth movements essoclated with the <br />slide are confined to the visible area of the elide. The northern pond embankment does <br />not show any signs of distress or movement. In our opinion, th• stability o1 the <br />embankment has not been reduced by the slide which has occurred. <br />REPAIR RECOMMENDATIONS <br />Repair of the slide should include removal of the failed soil mass, Installation o1 <br />drainage to collect seepage water, removal of the topsoil stockpiles to reduce slope <br />heights, benching of the base of the excavation end re-filling of the area. Excavation of <br />the slide mass will result In an exposed shelf of colic above the slide which will be In a <br />borderline stability condition. This overhanging slope should bo cut back as flat a <br />practical and observed to detect movement during the re-construction process. Access <br />of personnel to areas below this slope should be restricted, or protection provided untl <br />fllling is almost completed. Following are recommendations for repair of the elide area. <br />1. Tho topsoil stockpiled should bs removed from the area and the slope <br />uphill from the slide area flattened as much as practical.. The slide mass <br />should be excavated to the base of the slide. We anticipate this will be at <br />the intersection with the claystone layer, similar to condltlons found during <br />previous excavations of the lateral subdrelns. We recommend excavating <br />until und(aturbed material is encountered and the seepage source is <br />exposed. <br />2 <br />Prior to re-fllling of the area, we recommend that the base of the <br />excavation be benched to key the new fill into the layer as much as <br />practical. The benches should consist of a consistent series of steps. <br />After benching, <br />fill can then be placed end compacted to planned grades. <br />3 <br />LL!l:B5444ZAEOE HJOSdWOHl/l10 WdZO:E 56-A -L NOSdWOHl/110:1,8 1N3S <br />
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