Laserfiche WebLink
I~ Sylvester Gulch Facilities Area <br />Construction Aooroach And Construction Monitoring Program <br />for Potentially Unstable Sloaes <br />The following text describes MCC's proposed construction approach for the SGFA and the <br />construction monitoring program for potentially unstable slopes. The intent of this program is to <br />ensure the design and constnuction of cut slopes and final reclaimed configurations of these slopes <br />are stable based on real data and site specific field conditions. The program involves four main <br />activities: <br />1) Collection of geotechnical information in specific locations, and preparation of additional <br />slope stability analyses prior to constmction in these areas. <br />2) Detailed field monitoring including frequent on-site observations by environmental, <br />engineering and geotechnical professionals. <br />3) Using construction techniques which will minimize or mitigate potential slope failures <br />during and after construction. <br />4) Performing redesign and slope failure mitigation as required to ensure long term stability. <br />• Text on MCC's general constmction approach for the SGFA, and a Summary and Conclusions <br />section are included at the end of the document. <br />Part I Collection Of Geotechnical Information and Additional Slooe Stability Analyses <br />MCC has previously forwarded to the Division copies of past reconnaissance and field level <br />geotechnical reports, including mapping, supplemented by historic and recent site specific <br />geotechnical (borehole) data on soil and rock strength properties. As correctly noted in the <br />Divisions adequacy comments, these past reports are in agreement that the Sylvester Gulch <br />Facilities Area (SGFA) is subject to numerous, localized, slope stability problems, and that site- <br />specific investigations and analyses aze recommended prior to siting facilities within the area. <br />During conceptual design, MCC identified the need to collect specific soils data within the SGFA. <br />A drilling program consisting of 22 soil borings within the SGFA was conducted in August 1996 <br />to identify basic soil properties. Eight additional borings were completed in October 1996, <br />focusing on both shaft sites, and on the substation. This October 1996 investigation included <br />collection of samples at each location for determining soil strength properties. Additionally, <br />historic soil strength data for locations throughout the West Elk mine site were also collected and <br />analyzed. Summary tables of this information were included in MCC's previous response. <br />Based on the conceptual design plans and existing geotechnical reports, MCC and their <br />geotechnical consultant, Golder Associates, identified 8 locations within the SGFA ai which <br />stability analyses were necessary. Three of the eight areas, Sections A-A', D-D', and F-F' were <br />considered by MCC to be most critical, since they involved cut slopes within areas previously <br />mapped as active or potentially active slide zones. Sections A-A' and D-D' are road cut slopes <br />