2014-12-15_REPORT - M1980244 ‎(7)‎

• Permit No: M1980244
• IBM Index Class Name: Report
• Doc Date: 12/15/2014
• Doc Name: Response to Review Comment 7.c.
• From: CC&V
• To: DRMS
• Email Name: TC1
• Media Type: D
• Archive: No

ameO
December 12, 2014
Mr. Ron Roberts
Construction Manager
Cripple Creek&Victor Gold Mining Company
Post Office Box 191
100 North 3rd Street
Victor, Colorado 80860
RE: SGVLF PSSA Closure Drain Concrete Acceptance
Dear Mr. Roberts,
During construction of the Closure Drain portion of the Process Solution Storage Area (PSSA) in
the Squaw Gulch Valley Leach Facility (SGVLF), AMEC sampled the concrete used to construct
the collars around the closure drain pipes. A section of the concrete collars is shown in Detail 6
on Drawing A362 of the Issued for Construction Drawings. The concrete is specified to have a
28-day unconfined compressive strength (UCS) of 4,000 psi. The one concrete sample tested
for the 28-day UCS had a result of 3,190 psi, which is about 20 percent less than the required
strength. AMEC considers that although the concrete in the closure drain collars did not meet
the specification for UCS, the concrete still will adequately perform according to the design
intent.
The main purpose of the concrete collars was not structural, it was to prevent movement of the
steel casing and the Schedule 80 pipe for the closure drains during construction of the PSSA
sump area and provide a consistent location for record drawings. However, to alleviate
concern, a calculation of the maximum vertical stress anticipated at the concrete collar is as
follows:
Vertical Stress at Concrete Collar from Saturated Ore = (131.9 Ib/ft3 x 126 ft) = 16,620 psf
(115.4 psi)
where:
• 131.9 pcf is the saturated ore unit weight conservatively assuming the entire PSSA is filled
with solution
• 126 feet= height of ore above concrete collars
o 9452.14 ft (elevation of top of ore above the concrete collar) - 9,327 ft(top of
concrete collar) = 126 ft
The typical design dead load factor is 1.4*DL, in accordance with American Concrete Institute
(ACI) 318-11, Chapter 9. Using this design factor,
Total maximum design vertical stress = 1.4 x 115.4 psi = 161.6 psi.
Since the maximum vertical stress acting on the concrete collar is 161.6 psi and the measured
28-day compressive strength of the concrete was 3,190 psi, the factor of safety with respect to
compressive failure of the concrete is approximately 20, which is considered acceptable.
Additionally, the shear strength capacity of the concrete was calculated using ACI 318-11,
Equation 11-3 and 4) = 0.75 in accordance with ACI 318-11, 9.3.2.3.
AMEC Environment&Infrastructure,Inc.
2000 South Colorado Boulevard
Suite 2-1000
Denver,Colorado 80222
Tel: [phone] vwvw.amec.com Page 1