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.FRpM :, Yt1'ERS DSGN ENG~MINES GFOUP INC PHONE N0. 792?332413 Novi. 29 1°97 06:36Rn P2 <br />!II IIIIIIIIIIIII lll- <br />]lYC6IK'SLLT h.npubtiT111Y'. <br />tm~ <br />7C Kwl. ))rvrr Yhom<(rtL')hay3Wi1 <br />Inclin. ~",).`,~y~~. VV 1''~\: t7V:)i~4'~':a 1.9 <br />V;,ISI F..myil I~MymHYn+Ganl ~a,m <br />November Z0, 1997 <br />Mr. Charles Rehn <br />Harding Lawson Associates <br />155 South 300 West, Suite 103 <br />Salt Lake Ciry.1Tf &t I U 1 <br />Re.: West Elk Minc Landslide -Time to Failure Update <br />Deaz Mr. Rehn. <br />This letter and the attached figures represent an interim report on the update of the time <br />to failure predictions for the West EIk Mine landslide mass. Movcmetits of the landslide <br />mass have been monitored to some degree since 1993 and extensively since about 1996 <br />using surface monuments aad conventional surveying techniques. Displacemenu <br />accelcnted dramatically In the spring of 1997 and emergency stabilization measures <br />were implemented in the critical production corridor containing the existing crushing and <br />screening plant and the associated conveyor system. A roller compacted concrete buaras <br />with tiebacks was installed in May of 1997 which effectively arrested much of the <br />movement in the production corridor. At that time monitoring data indicated a high <br />probability of catastrophic macro failure of the production corridor in mid May to cazly <br />June of 1997 if no action was talon. Implementation of the emergency measures have <br />altered stability conditions dramatically and a review of the monitoring data is now <br />warranted to chazactcriu the remaining risk <br />The monitoring data indicates movemrnt on multiple failure planes at many of the <br />monitoring sites (existing data would indicate from one to three distinct failure planes <br />depending un the location of the monitoring station on the landslide mass). Displacemrnt <br />rates and changes in the displacement tale (acceleration) have been extracted from the <br />monitoring data at each monitoring station for each identifiable failure plane. Failure <br />planes have beat classified into three categories depending on their displacemem rate <br />and behavioral characteristics. The three classifications used arc designated A, B, or C. <br />The designation does not imply a "physical" connection (i. e., plane A at one station may <br />not physically be the same failure plane as plane A at another station, but it does possess <br />similaz characteristics). <br />The A hpe planes well trnd m have the highhest displacement rates and tend to activate <br />only intermittently during the periods of highest moisture (high rainfall, rapid snow melt, <br />