PERMFILE64662

• Permit No: C1980007
• IBM Index Class Name: Permit File
• Doc Date: 12/11/2001
• Section_Exhibit Name: Exhibit 14A Landslide Study Geo-Hydro Consultants 1980
• Media Type: D
• Archive: No

5
It is very difficult to interpret the character and the
depth of the landslide deposits. We believe that two types of
Landslides can be classified on the site:
1. Large, old landslides that occured a long time ago,
possibly during the Pleistocene time under different climatic
conditions. These landslides included not only surficial soils
but also the bedrock. Flat benches and gener;slly hummocky topo-
graphy of the area are a result of this type of sliding.
Slides could easily develop in geological conditions where
a water-bearing coal seam was underlain by an impervious layer
of shale or claystone; long-term exposure of the shale layer to
the water caused significant reduction of the shale strength and
shearing resistance. As a result of potential high ground water
pressures, a slide could easily develop; the slip plane of the
failure follows the contact between the coal and shale and then
in a step-wise mode vertical joints and bedding planes in rock
above the coal seam.
~i
Slides of this type are fairly common; they can be observed
yin the Mesaverde formation in the vicinity of the Mount Gunnison
''.mine; some of them are very recent. They are not always related
.;
'~'~to the presence of the coal seam; a water bearing sandstone
;,layer has a very similar effect on the stability.
2. Smaller, surficial slides that have been occurring
recently. These slides. are limited to the surficial solid cover
only. Above five of them are indicated on the geotechnical map;
the slide directly above boring P1 is the largest one and, at
the same time, the most recent one as it has developed during
the last months.
The development of these slides is closely related to the
general instability of the area after the initial development of
~; large landslides of the first group; unfavorable hydrological
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