2010-06-16_PERMIT FILE - M2009077

• Permit No: M2009077
• IBM Index Class Name: PERMIT FILE
• Doc Date: 6/16/2010
• Doc Name: Review of Slope Stability Analysis
• From: DRMS- psh
• To: DRMS- mac
• Email Name: MAC
• Email Name: PSH
• Email Name: AJW
• 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]
DATE: June 16, 2010
TO: Michael Cunningha
FROM: Peter Hays
COLORADO
DIVISION OF
RECLAMATION
MINING
SAFETY
Bill Ritter, Jr.
Governor
James B. Martin
Executive Director
Loretta E. Pineda
Director
RE: Review of Slope Stability Analysis, Tracy and Ed Grimes, Dill Pit, File No. M-2009-077
The Division of Reclamation, Mining and Safety (DRMS) staff has reviewed the stability analysis included
with the Dill Pit, File No. M-2009-077, permit application. The report specifies setback distances from the
edge of mining in the proposed pit to the edge of the road base of County Road 189. 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 25 feet from the East Right-of-Way and 39 feet
from the edge of the road base of County Road 189.
2. Mineral will be mined down at a maximum 4 to 1 slope.
3. The excavation will remain a minimum 2 feet above ground water.
4. The maximum depth excavated will be 25 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 according to Peck, et al. and Meyherfhof.
6. Soils on the site are classified as SP-SM (poorly-graded sand and silty sand) with some SP and SM.
7. An analysis was performed using the formula; minimum safety factor (SF) = friction angle / degree
of slope. Using a friction angle of 34 degrees and a 14 degree slope angle, a 2.4 safety factor 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 three cross sections for the Dill Pit. Specific comments and requirements for each of the cross
sections are provided below.
Cross Section No. 1
The applicant's cross section was duplicated for verification with the addition of the topsoil stockpile; no
potential failure surfaces with lower safety factors than the applicant's calculated safety factor were
located. The safety factor produced by Galena is slightly higher than that produced by the applicant's
formula. Therefore, the accuracy of the applicant's analysis is confirmed (see attached).
Office of Office of
Mined Land Reclamation Denver • Grand Junction • Durango Active and Inactive Mines