REV13077

• Permit No: M1978305
• IBM Index Class Name: Revision
• Doc Date: 8/4/2000
• Doc Name: HIGHWALL STABILITY GUNNISON GRAVEL DICKERSON PIT PN M-78-305
• From: DMG
• To: BOB OSWALD
• Type & Sequence: CN1
• Media Type: D
• Archive: No

RUG. 1.2000 4: 13PM DIViMINERRLS&GEOLOGY N0.330 P.2i4
• •
ordut soil slope. If the rock classifies as R2, moderately weak rock, further tosting to determine
the s eaz strength of the rock would be required to decide if it could be benched or terraced for
rec ~ anon. Rock that classifies at R3 or higher is not likely to fail through the intact rock, and
only a fracture orientations would be of concom.
3. Day ghted fracture or joint seu aze potentially subject to plane shear sliding failure whenever the
free is flatter than the slope angle and steeper than the angle of surface friction along the
Erne e. The resistance to sliding along the natural joints must be exceeded by the down dip thrust
of th potential sliding block of rock for a failure to occur. Resistance to sliding along joints is
prov tied by friction created by the weight of the rock above the joint, the roughness and irregularity
of th joint surfaces, whether the joint is open or closed, and if a mineral iafilling heals the joint,
Oth factors that influence the degree of resistance to sliding are the dip angle, presence or absence
of w r, if there is a clayey ar slickenside fracture surface, and the presence, oxtent, and strength of
inta rock bridges across the fracture surface. The personnel assigned to measure and map the
es must make observations of these features and log them in the field notes to make a
tom late evaluation of the stability of the proposed highwall configuration. The field
me urements and observations maybe used to estimate the proportion of broken and intact rock
alo potential joint failure surfaces, Observations and testing maybe used to estimate the strengW
of ' tact rock bridges if they are present along adverse fracture orientations.
4. if a verse fractue orientations are present at the Dickerson Pit, it maybe necessary to conduct a
phy ical testing program to determine if the proposed pit wall configuration will be stable in rite
ion term, A testing program would typically include uniaxial and triaxial testing of n:presenrative
s les of the different types of rock exposed in the quarry, as well as direct sheaz testing of
fine resurfaces to estimate the degree of shearing resistance available along the fractures.
She g resistance along adverse fracture orientations can be adjusted to include the influence of
fr irregularity and intact rock bridges, and can be applied in limiting equilibrium slope
stn ility analyses. These analyses simply compaze the forces tending to cause movement (the force
of ravity on a rock mass above a fracture surface) to the force resisting movement, which are the
Erie 'onal forces. A ratio of these forces yields the safety factor for the pit wall. Any safety factor
ab a one, if the inputs to the ratio are accurate, indicates that the pit wall wil! be safe.
5. As ontiaued quarrying encroaches upon the final pit wall location, it is important that intacirock
b ' gas along any adverse fracture orientations are preserved to ensure long term stability.
uction blasting practices tray potentially damage or destroy the rack bridges. If adverse
cure orientations aze present at the Dickerson Pit, the Operator maybe required to commit to a
p cter blasting plan. This plan would allow the Operator to employ standard production blasting
p rites in the majority of quarry operations, As the f"mal pit configuration is approached, alternate
bl ring practices could be implemented to protect the integrity of rock bridges. Such practices
iv tide cushion blasting, precision blasting, smoothblasting, and presplit blasting.