PERMFILE54329

• Permit No: M2007044
• IBM Index Class Name: Permit File
• Doc Date: 11/14/2007
• Doc Name: Cost estimate for water impounding concrete bulkheads
• From: DRMS
• To: File
• Media Type: D
• Archive: No

Memo to Russ Means 6 November 14, 2007
Bulkhead Cost Estimate File No. M-2007-044
Design for Concrete Sheaz on Pack Rat Mine Perimeter
The required bulkhead length for the concrete sheaz component of design, assuming minimum bulkhead
concrete compressive strength is specified at 3000 psi, is calculated as follows:
L_ pxhx2 _ 116x9x12 =27feet
2x~h+P~x f's 2x9+12x110
where: L =bulkhead length (feet)
p =pressure head (psi)
h = adit height (feet)
P = adit width (feet)
f', =concrete sheaz strength (psi)
Therefore, the 2.8 foot minimum bulkhead length required for pressure gradient slightly exceeds the
bulkhead length required for concrete sheaz, and pressure gradient controls the design.
Design of the Pack Rat Mine Contingency Bulkhead for Construction Cost Estimating Purposes
The basic design elements for the Pack Rat Mine bulkhead are as follows:
Note: one foot added to Whirlwind Mine workings dimensions to account for notching of bulkheads
• bulkhead dimensions aze 13' x 10' x 2.8' long
• bulkhead volume is 13.5 cubic yazds
• low pressure grouting is necessary
• flexural and temperature shrinkage rebaz at both ends of the bulkhead, both ways
• stainless steel bypass and monitoring piping is necessary
• Concrete will use maximum'/4 inch aggregate, Type V cement, 16 percent fly ash, pozzolan,
water/cement ratio of 0.45 by weight, and will be over sanded to enhance pumpability
Bulkhead Construction Cost Estimate
DRMS has estimated the cost to install the three bulkheads described above at $531,247.00. This
estimated cost includes all indirect costs and the five percent administration cost required by statute. The
estimated costs are detailed in the worksheet memo enclosed. The estimate uses adjusted unit costs
incurred during the construction of the Terry Tunnel bulkhead in the Sunnyside Mine during the mid-1990s.
A copy of the detailed Terry Tunnel bulkhead costs is also enclosed with this memo.
Verification of Bulkhead Effectiveness
For water impounding bulkheads in underground mines to be effective, there must be no significant
hydrogeologic flow path between the impounded mine pool and surface water bodies. Demonstration of
this is done through establishment of baseline surface hydrology conditions and monitoring for
perturbations to baseline following bulkhead installation. Ground water tracers can be a useful tool. The
ongoing hydrologic monitoring plan to be required for the Whirlwind Mine (see DRMS memo: Kate
Pickford to Russ Means, 11-8-07) must focus on establishment of a baseline that will be useful in
demonstration of eventual bulkhead effectiveness. In addition, and as discussed above, in the Whirlwind
Mine setting where there aze multiple aquifers in a relatively flat lying sedimentary stratigraphy,