PERMFILE64469

• Permit No: M2001046
• IBM Index Class Name: Permit File
• Doc Date: 4/23/2002
• Doc Name: Slope Stability Analysis
• From: Al Amundson
• To: Tony Waldron
• Media Type: D
• Archive: No

STATE OF COLORADO
DIVISION OF MINERALS AND GEOLOGY
Department of Natural Resources
1313 Sherman St., Room 215
Denver, Colorado 80203
Phone: [phone]
FAX: [phone]
To: Mr. Anthony Waldron
From: AI Amundson
Memo
Apri123, 2002
DIVISION OF
MINERALS
GEOLOGY
RECLAMATION
MINING•SAF ETY
Bill Owens
Governor
Greg E Watcher
Executive Director
Subject: M-2001-046 Nix Sand and Gravel Mine Slope Stability Analysis, Dated Michael B. Long
Division Director
February 28, 2002.
The Division of Minerals and Geology (DMG) has performed a review of the slope stability analysis
for the subject property performed by Banks and Gesso, LLC. This review has raised some
questions and comments.
The analysis appears to be based upon slopes of 2:1 with a limit of mining within 90 feet of
structures including overhead powerline, and county roads. It appears that the Operator is proposing
an engineering evaluation to satisfy the requirements of Rule 6.4.19(b) which states "where such an
agreement (to allow mining within 200 feet) can not be reached, the applicant shall provide an
appropriate engineering evaluation that demonstrates that such stmcture shall not be damaged by
activities occurring at the mining operation."
They are also asking for a variation of Rule 3.1.5(7) which states "Maximum slopes and slope
combinations shall be compatible with the configuration of surrounding conditions and selected land
use. In all cases where a lake or pond is produced as a portion of the Reclamation Plan, all slopes,
unless otherwise approved by the Board or Office, shall be no steeper than a ratio of 2:1 (horizontal
to vertical ratio), except from 5 feet above to 10 feet below the expected water line where slopes
shall be not steeper than 3:1."...
The consultant performed a slope stability analysis using GSLOPE from MITRE Software
Corporation, which yields a factor of safety of 0.90 on the west and 0.97 on the south. These factors
of safety are reached using assumed values for material weight, cohesion, and angle of internal
friction as no laboratory test values are available for the specific soils.
The DMG normally accepts factor of safety values ranging from 1.25 to 1.5 as demonstration of
stability. Factors of safety of less than 1 are indicative of failure or creep in the soils, and therefore
do not demonstrate stability.
Assumed values are occasionally acceptable with a higher than normal factor of safety in certain
cases, but since this analysis is using assumed values, and yields factor of safety of less than 1, the
DMG cannot accept this as a demonstration of stability.