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Y <br />III IIIIIIIIIIIII III <br />STATE OF COLCJi~n9i ~u <br />DIVISION OF MINERALS AND GEOLOGY <br />Dcpdrlmrnl ul Natural Rewurc e5 <br />1 f I f Sherman 51., Kuom 215 <br />Dcnvor, Colorado HO_'D1 <br />Phone Ifl){I 7466-1567 <br />FA%.14(151 t1 S_'-fl IOL <br />DATE: September 12, 1997 <br />TO: Mike Boulay <br />FROM: Jim Pendleton <br />RE: West Elk 'ne - er <br />(Pe it No: <br />~1 <br />Sylvester Gulch Road Redesign <br />C-80-007) <br />I~~~~ <br />DEPARTMENT OF <br />NATURAL <br />RESOURCES <br />Rny Kamrr <br />Governor <br />lames S Lochhead <br />E~rcuove D~rrUO! <br />Michael B Lonq <br />Division Director <br />I have reviewed the West Elk Mine Geotechnical Report, covering the <br />August 18 - August 29, 1997 time period. This report includes <br />comparative back-calculated stability analyses of proposed <br />configurations for the portions of the lower Sylvester Gulch road <br />adjacent to inclinometer I-4. It also includes references to <br />alternative amended configurations within those analyses. <br />Briefly summarized, Golder & Associates recommends laying the cut <br />slopes back from 1.5:1 to 2.0:1 (h:v). Further, the obvious <br />conclusion from the alternative water table assumptions is that the <br />ground must be dewatered to remain stable. MCC proposes to install <br />additional french drains to accomplish dewatering of the slopes <br />above the lower Sylvester Gulch road. <br />I do not disagree with Golder's conclusion. Golder and MCC have <br />determined that (1) the Williams Fork formation of the Mesa Verde <br />group is prone to landsliding, and (2) landsliding is exacerbated <br />by pore water pressure. I am concerned, however, with MCC's <br />ability to effect dewatering of the subject slope with simple <br />french drain installations. The french drain installations I have <br />observed at the SGFA to date are relatively shallow (approximately <br />3 to 5 feet deep), gravel-filled trenches. MCC prefers to install <br />the french drains after excavation of the cut slopes. In the case <br />of the extensively saturated slopes above the lower Sylvester Gulch <br />road, I believe more extensive french drains may be required. I <br />also believe the drains should be installed prior to excavation, in <br />order to provide prophylactic dewatering of the threatened ground. <br />I am also concerned that the inclinometer and piezometer <br />installations at I-2 and I-4 will probably be destroyed in the <br />process of excavating the flatter slope configurations. In my <br />opinion, inclinometers should be installed immediately above the <br />highest cuts before the excavation is commenced. These <br />installations will verify the success of the stabilization efforts <br />or provide warning of impending instability. Similarly, <br />