REP33070

• Permit No: C1980007
• IBM Index Class Name: Report
• Doc Date: 10/29/1981
• Doc Name: Upper Waste Rock Pile - Prelim. Stability Evaluation
• From: Geo-Hydro Consulting
• Permit Index Doc Type: STABILITY REPORT
• Media Type: D
• Archive: No

' - 12 -

The landslide area was studied in more detail only at
' the location where surface facilities or structures of the
future coal mine are proposed. Attention was paid mainly to
' the design of the portal bench and individual entries to the
mine.
'
We believe that the landslide or individual landslides
had developed in the past as a result of the failures of the
crest of the upper bench. The interpretation of the sliding
mechanism is based on the observations from the site and from
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other parts of west Colorado.
1
The landslide mechanism is believed to be a process of
' the degradation of benches that had been formed previously
by erosional processes. Intermediate, fairly steep slopes had
' been created between individual benches; these slopes had
safety factors close to unity and landslides could easily
develop in them.
' Typically, unfavorable hydrologic conditions might have
influenced the stability if ground water was present within
the relatively pervious coal seam below the bench. Ground
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coal-underlying shale or claystone; the properties of these
' rocks could have been considerably degraded by the presence o
water. Piezometric pressures within the coal contributed
' Further to the instability. It is also possible that ad-
ditional aquifers which were present above the coal seam
' further decreased the stability of the slope.
' Factors of safety of the slope could then have dropped
below unity. As a result, lateral deformations of the slope
ccoeroao ca+w~nxc, n+c.