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CONCLUSION
<br /> The purpose of this memorandum is to present the calculations supporting a proposed bulkhead extension at
<br /> Times Mine. To allow ring grouting, rock bolt installation, and provide a suitable pressure gradient, the typical
<br /> minimum bulkhead length for constructability is approximately 8 feet. Since the Times Mine has an existing
<br /> bulkhead that can take the place of a row of rock bolts for ground support, the length can be shortened to 6
<br /> feet, without affecting constructability. As shown in the table above, a 6 foot bulkhead still provides adequate
<br /> factors of safety and therefore meets the design criteria. The only design criteria that is not met using the more
<br /> conservative Norwegian method is hydraulic jacking. The calculation is based on the bulkhead depth which is
<br /> based on its location. Since the old bulkhead is already in place and cannot be moved unless the mine pool is
<br /> drawn down, the location is fixed. There is no other solution although grouting the rock mass around the
<br /> bulkhead can mitigate effects near the bulkhead. To mitigate risk, the bulkhead, adit, surrounding slope, and
<br /> road should be monitored for seepage when mine pool levels are above 57 feet.
<br /> REFERENCES
<br /> Abel Jr., J.F., 1998, "Bulkhead Design for Acid Mine Drainage," in Proceedings Western U.S. Mining-Impacted
<br /> Watersheds, Joint Conference on Remediation and Ecological Risk Assessment Technologies, 36 Pages,
<br /> Denver, Colorado, USA
<br /> Byron, J.E. and Reardon, A.E., Wynona Mine Profile dated 1934
<br /> Chekan, Gregory J, 1985, "Design of Bulkheads for Controlling Waters in Underground Mines," Bureau of
<br /> Mines Information Circular, 9020
<br /> Einarson, D.S., and Abel Jr., J.F., 1990, "Tunnel Bulkheads for Acid Mine Drainage," in Proceedings
<br /> International Symposium on Unique Underground Structures, Vol. 2, Pages 71-1 to 71-20, Denver, Colorado,
<br /> USA
<br /> Garrett, W.S., and Campbell-Pitt, L.T., 1961, "Design and Construction of Underground Bulkheads and Water
<br /> Barriers," Seventh Commonwealth Mining and Metallurgy Congress, Vol. 3, Pages 1283 to 1301
<br /> Kirkwood, D.T., and Wu, K.K., 1995, "Technical Considerations for the Design and Construction of Mine Seals
<br /> to Withstand Hydraulic Heads in Underground Mines," Society for Mining, Metallurgy and Exploration Annual
<br /> Meeting Preprint 95-100
<br /> Lang, Brennan, 1999, "Permanent Sealing of Tunnels to Retain Tailings or Acid Rock Drainage," in Mine,
<br /> Water, and Environment, 1999 IMWA Congress, Sevilla, Spain
<br /> McLellan, Russel R, Times Mine Geologic Map Plan View, 1947
<br /> ATTACHMENT:
<br /> Design Calculations in MathCAD and MS Excel for 6 and 8-foot long bulkhead.
<br /> Project 22690002.000 7/18/2022 Page 4 Schnabel Engineering,LLC
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