2009-09-17_REPORT - M1987049

• Permit No: M1987049
• IBM Index Class Name: REPORT
• Doc Date: 9/17/2009
• Doc Name: Stability Exhibit for the Bromley Lakes Sand and Gravel Pit
• From: DRMS
• To: Ready Mixed Concrete Company
• Media Type: D
• Archive: No

Table 1: DRMS Model Parameters
Soil Type
Effective
Friction Angle
0' (degrees)
Effective
Cohesion
c' (psf)
Saturated Unit
Weight
Xat (pc)
Overburden
28
50
126
Gravel
35
0
137
Weathered Bedrock
14
0
142
Bedrock
28
100
142
In our opinion, the parameters for weathered bedrock are very conservative based on the conditions
typically encountered in the project area.
In accordance with the DRMS guidelines, we analyzed a vertical highwall section. The vertical section
corresponds to a steep highwall mining scenario where the highwall inclination is approximately 0.5:1
(horizontal to vertical). The depth to bedrock varied from 311/ to 51 feet across the project site.
Table 2 below summarizes the results of our analysis. The analysis was performed using the DRMS
parameters shown in Table 1. The factor of safety required by the DRMS for temporary mine slopes
and reservoir embankments are provided for comparison. Output graphics for each of the analyses are
attached.
Table 2: Highwall Setback DRMS Analysis Results
Model
Setback
Distance (feet)
Calculated
of
FS fety
Required Factor
of Safety
Adjacent to Brighton Road
50
1.17
1.0
Adjacent to Spier Property
45
1.14
1.0
Near McCanne Ditch
65*
1.08
1.0
*the above setback distance is from the existing ditch
The required setback distance provided in Table 2 is calculated from the crest of the mine highwall to
the potential failure surface intersection with the existing ground surface. If the McCanne ditch is to be
relocated we recommend that a new setback distance is analyzed in the future based on the design of the
relocation.
P \0377 Hatt Envrronmental\Bromley Lakes Stabthty Analyan\Stabthty Enhibu\Bromley Lake Stabtlay Eahtbtt doc
Bromley Lakes
DRMS 112 Permit
Page SE2 of SE2