Laserfiche WebLink
1 2-8d-1 997 9: 01 AF1 FF.Ot4 ENG. WEST ELK t.1I IVE 970 9295C~5~ P. 1 1 <br />-.~~i ine~D Yb~N tMa/r'IiNt~ bkUlk' INC PHONE Np. 7928:324:3 Nov. 20 199; 0e:37gtt P3 <br />etc.), When acive they tend to mask the presence of the other failure planes and <br />dominate the measured tlisplacetnertts <br />8 type plants tend to have more moderate duplaccment tares and aze also intermittent <br />but remain active over longer periods of time that can extrnd well into the dryer periods <br />~ of the year. <br />C type places tend to have the lowest displacemem rases and represent a steady, virtually <br />ever present creep throughout the landslide tt19GC that Is independent of the periods of <br />high moisttur. <br />The measured surface displacements represent rho cumulative disphiccmcai oa all of the <br />failure plants present at a given monitoring station. Therefore, in order to assign <br />duplacemcnt rates to the individual planes, a correction must be applied to remove the <br />background dtsplacetutat on the slows[ plane to provide the best estimate of the actual <br />displat:emem raid oa the next fastest plane. All of the displaceairnt rates depicted in the <br />figures accompanying this letter love barn corrected in this manner. <br />There are any number of methods for ptt:dictiag time to catastrophic failure from surface <br />disptaccmem data, all of which attempt to "linearize" the data for the purpose of making <br />future prYdietions. The two methods selected fw use wuh the data at the West Ells site <br />ate Inverse Velociry and Logarithmic Aisplaccmetrt Vclxiry. Inverse Velocity tends to <br />be best in the late stages of acceleration just weeks prior to a po-rntia! macro failure <br />while tlw Logarithmic Displacement Velocity method tends to be better (i.e., more <br />consistent end stable) for long range projet:tioas of time to failute. <br />Review of the post-RCC buttress monitoring data indicates that movtmeat oa the A and <br />B planes was effectively arrested by the buttress at monitoring sites 13, 14, 15, and 22. <br />Movemetu on place A only was azrested at mottitoriag sites 5, 10, t 1, 23, 24, 29, and 31. <br />Movements on plane A wets impacted but not arrested at monitoting sifts 4, 25, aad 28. <br />The remaining monitoring sites continue to displace with minimal impact from the RCC <br />buttress <br />Review of the figur>r showing inverse Velocity fns A plena only shows rttaflerous <br />stations with predicted time to failure (i.e., interception of the irrvet5e velocity - 0 line) <br />is the spriasr_ summer and fall of 1997. However, all of these were effectively arrested by <br />the RCC buttress with the exception of 28 which was impacted (slowed) but not arrrned. <br />There are two additioaat stations of concrn on this figure which are station 27 with a <br />projected Failure date of March 1998, and station 16 with a projected Cailure date of <br />January 1999. However, the Logazithmic Displacement Velociry plot for A planes only <br />would project failure dates of Ocmbcr 1998 cad Juae 1998 for stations 27 and 28 <br /> <br />