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12-0a-1997 9:OL4t-1 FPOt1 ENG. WEST ELK tdINE 970 9295C~Sf~ P. 1Cn <br />rnuri rn~htD yAlaN tNt,~H1NE5 Gr'IpUP INC PHpn@ NQ. ~ 7929 3 324 1? rro~. 20 1P°7 06:%an P2 <br />NYCr5 tS~1L•~l.npu>,Rfplq. <br />lN'. <br />7C tiWlr 1)rirc Ylwac: (7V')K44.W0.d <br />Grl(n. •~Ly~,vV 1'aa tRR)d'Q~?SIR <br />Uwl t:.myil. A!S~CI'S~`.R)X{lanl Haim <br />November 29. 1997 <br />Mr. Charles Rehn <br />Harding Lawson Associates <br />-. <br />155 South 300 ~'/~~st, Suite ]03 <br />Salt Lake City. Lfi 84101 <br />Re.: West Elk Minc Landsiidc - Time to Failure update <br />Dcaz Mr. Rehn. <br />This letter and the attached figures represecrt an ia[erim report on the update of the time <br />to failure predictions for the West Elk Mine landslide mass. Mwemerrts of the lattdslidr <br />mass have been monitored to some degree since 1993 and extensively since about 1996 <br />ruing surface monuments and conventional surveying techniques. Displacements <br />accelerated dtamattically in the spsiag of 1997 and emergency stabilization meastues <br />were implemented in the ctitical production coctidor containing the existing cttuhing and <br />screening plant and the associated t:omryor systcra A roller compacted concrete buttress <br />with tiebacks .vay installed In May of 1997 which effectively arrested much of the <br />movement is the production corridor. At that time monitoring data indicated a high <br />probability' of wtasuophic macro failure of the production corridor is mid May to esrly <br />June of 1997 if no action was takrn. Implementation of the emergency measures have <br />altered stability conditions dramatically and a review of the monitoring data is now <br />~ warranted to characteriu the remaining risk <br />The monitoring data indicates movement on multiple failtue 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). Displacement <br />cares and changes .in the displacement rate (atxelcration) have been extruted from the <br />monitoring data at each monitoring sffition for each identifiable failure plane. Failure <br />planes have been classified into three categories depending on their displacemcm rate <br />and behsviorsl characteristics. The three dasi5carioto used azc desrgrtated A. B, or C. <br />The designation does not imply a "phvsicaJ" connection (i.e., plane A at one station may <br />not physiwliy be the same Cailtue plane as plane A at another station, but it does possess <br />similaz chatactenstics). <br />The A type planes will tend W have the highest displacement rates and tend to actuate <br />only intermitternly during the periods of highest moisture (high rainfall. rapid snow melt, <br /> <br />