PERMFILE71422

• Permit No: M1980047
• IBM Index Class Name: Permit File
• Doc Date: 9/22/1975
• Doc Name: SUMMARY
• Media Type: D
• Archive: No

~ESIGN METHODS IN ROCK MECHANIC
INTRODUCTION
During 1973-1974, Atlantic Richfield Company,
Operator of the Colony Development Operation,
initiated the design and first stage construction of
the United States' first conmercial size shale oil
plant near Grand Valley, Colorado. Although con-
struction of the project was indefinitely deferred
late in 1974 due to uncertainties regarding national
energy policy and the state of the economy, the work
completed to date has required the application of
modern design criteria to very unusual conditions.
The shale oil complex was to be constructed on
the Roan Plateau (elevation 8100 feet - 2469 m) on
the drainage of Parachute Creek, a tributary to the
Colorado River. A plant at this location required
construction of a high quality access road beginning
in the Parachute Creek Valley at about elevation
6450 feet (1966 m), and was complicated by right of
way restrictions and the rugged topography in the
canyon.
The deep canyon is characterized by extensive
talus slopes standing at or near their natural angle
of repose, about 38•, with vertical or subvertical
walls of considerable height above. Atypical cross
section of the canyon is shown in Figure 1.
deals with the design of that portion of the road
loci ted within the vertical to subvertical cliff
serious.
GEOS_LHNICAL CONDITIONS
The Roan Plateau region is a conspicuous high-
lan'_ located in the central portions of a large
intermontane basin and is typical of an arid,
maC~rely dissected plateau. It is cut by both
intermittent and perennial streams of dendritic
pa Yerns which have cut narrow, steep-sided valleys
or c=_ep canyons with precipitous walls in the sedi-
mentary rocks. Hanging valleys and box canyons are
characteristic of i:he area.
The stratigra{rhy of the region is dominated by
the Green River Formation, a lacustrine deposit of
the Eocene (Tertiary) Age which occupies the large
str:ctural basin of Piceance Creek. The rocks are
essentially horizontally layered. As can be seen on
Fic;re 1, two memblrrs of the Green River Formation
outcrop in the ca n_~on -- the upper Evacuation Creek
mercer and the lower Parachute Creek member
(Bradley, 193}).
Evacuation Creek rocks consist of shales, silt-
stores, and sandstones of }ow competency. They are
0 100 200 3CO FEET
Figure 1. Typical cross section of the canyon.
The road crosses these formations at a nearly
continuous grade of 8 percent. Embankments were not
economically feasible in most areas, particularly in
the cliff sections, and the road was designed as a
cut section with a total excavated width of about
60 feet. In the cliff formations this resulted in
rock cuts of several hundred feet deep. This paper
usually thin-layered, deeply weathered and tend to
weaJrer into rolling hills with slope angles of
25 to 38 degrees.
Parachute Creek rocks consist primarily of
co.-cetent and hard marlstones and shales, with no
ap;reciable weathering. (Technically, the shales
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