2010-09-16_PERMIT FILE - M2010047

• Permit No: M2010047
• IBM Index Class Name: PERMIT FILE
• Doc Date: 9/16/2010
• Doc Name: Review of Slope Stability Analysis
• From: DRMS-psh
• To: DRMS-mac
• Email Name: MAC
• Email Name: PSH
• Media Type: D
• Archive: No

STATE OF COLORADO
DIVISION OF RECLAMATION, MINING AND SAFETY
Department of Natural Resources
1313 Sherman St., Room 215
Denver, Colorado 80203
Phone: [phone]
FAX: [phone]
COLORADO
D I V I S I ON OF
RECLAMATION
MINING
SAFETY
Bill Ritter, Jr.
Governor
DATE: September 16, 2010
TO: Michael Cunningham
FROM: Peter Hays
Mike King
Executive Director
Loretta E. Pineda
Director
RE: Review of Slope Stability Analysis, Miller Family Investments, LLC, Lone Tree Pit, File No.
M-2010-047
The Division of Reclamation, Mining and Safety (DRMS) staff has reviewed the stability analysis included
with the Lone Tree Pit, File No. M-2010-047, permit application. The report specifies a setback distance
from the edge of mining in the proposed pit to the edge of the right-of-way for County Road 37 and 96.
The report includes technical slope stability analyses in support of the proposed setback specifications.
The following list describes the information used by the applicant to analyze slope stability for the
proposed pit:
1. The excavation of minerals will start no closer than 30 feet from the permit boundary line.
2. The side slope will be mined and reclaimed at a 3H:1V slope.
3. The excavation will remain a minimum 2 feet above ground water.
4. The maximum depth excavated will be 20 feet.
5. No laboratory strength tests were performed on soils at the site. The soil strength parameters
used were based on typical values for anticipated soils from Stability Analysis of Earth Slopes by
Huang.
6. Soils on the site are classified as SP (poorly-graded sand).
7. An analysis was performed using the formula; Factor of Safety (FOS) = Tangent of Internal Angle of
Friction / Tangent of Actual Angle of Failure Surface. Using a friction angle of 37 degrees and a 9
degree slope angle, a 4.8 factor of safety was calculated.
8. Groundwater levels were not accounted for in the stability analysis.
Using Clover Technology's Galena v5.01 slope stability software, the DRMS conducted further analysis of
the two cross sections for the Lone Tree Pit. Specific comments and requirements for each of the cross
sections are provided below.
Office of Office of
Mined Land Reclamation Denver • Grand Junction • Durango Active and Inactive Mines