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~-~~~ <br />~. _ ; <br />+< 3625E 42nd Strav. <br />,r Tucson, Arizona 85713 U.S.A. <br />(602)745-8141 <br />Cable: RDCINC <br />Telex: 666 492 <br />August 6, 1984 <br />Mr. Dave Hyatt Permit#: K-I~r27-OC7~ Confidental?: <br />Homestake Mining Company Class: Gam. ~a ?,ype-S <br />From: C61-LL E A~tc NrsL4S l o: ~~~,LP <br />320 North Main ~, <br />Gunnison, Colorado 81230 Doc. Name: i~fz,Pr~2,t <br />Doc. Date (if no date stamp): ~ -(fl - 8~ <br />Dear Dave, <br />In response to your questions regarding reclamation of the Pitch <br />east wall, I have the following comments. <br />1) Displacement Rate <br />With the cessation of mining, the slope should become increasingly <br />stable as the displacement shifts the slide mass to a more stable con- <br />figuration. Because of the high relief and the water from the snowpack, <br />the area is geographically active, with landslides and slope creep com- <br />mon natural phenomena. Therefore, it is unrealistic to expect the slope <br />to reach a zero displacement rate. <br />My recommendation is that you plan to do the reclamation when the <br />displacement rate is less than 6 in. per year. At that rate, raveling <br />and vegetation growth should heal tension cracks and other evidence of <br />displacement. <br />At the present time the smile crack is ponding water, which adds <br />to the instability. When the slope is dressed up and the ponding <br />eliminated, the displacement rate should drop significantly. <br />2) Lon>;-Term Stabilit <br />The slide is contained by the west wall of the pit; so the maximum <br />displacement is restricted. Thus, the environmental impact of slope <br />movement would be limited to the development of tension cracks and <br />scarps in an area where natural rock and soil scarps are common. <br />3) Groundwater <br />The primary factor affecting stability will be the spring snow <br />melt infiltrating and causing the groundwater level to rise. This dis- <br />placement rate will be seasonal and will vary from year to year depend- <br />ing on the snowpack. Winters such as the last several years where early <br />and heavy snowfall produced a high water content snowpack on unfrozen <br />ground will show more impact than years when there is a light snowpack <br />on frozen ground. <br />4) Monitori <br />If displacement rate is to be a criteria for selecting the time <br />reclamation is done, the slope will have to be monitored. <br />Geological Engineering Slope Stability Rock Mechanics <br />