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September 3, 2003 <br />To: Mr. Wally Erickson <br />From: James Dillie <br />Re: Bulkhead Design Review, Koehler Mine <br />Per your request, I reviewed the Koehler bulkhead designs that Mr. Steve Fearn submitted to the <br />Division. <br />As before, I did not verify Mr. Abel's design calculafions. <br />Mr. Abel's design report appears to follow the same criteria that were utilized at the Sunnyside <br />and Mogul mines (which, so faz, appear to be successful). The bulkhead needs to be designed <br />and constructed to contain acid mine drainage so the following design items are being <br />considered: 1. the bulkhead must be long enough and sufficiently sealed with grout to prevent <br />leakage along the concrete-rock contact and nearby fracture systems, 2. the bulkhead needs to be <br />thick enough to prevent shear failure or tensile failure, 3. the bulkhead needs to be located deep <br />enough to prevent hydrofracturing of the formation, 4. the bulkhead material needs to be <br />sufficiently acid resistant to last for some time interval and S. the bulkhead needs to be strong <br />enough to resist the effects of a maximum credible earthquake. According to Mr. Abel's <br />calculations, the Koehler bulkhead design meets all of the design criteria. <br />In my opinion, the bulkhead design for the Koehler tunnel is acceptable. <br />Sorry for the delay Wally. <br />cc: Harry Posey (e-mail) <br />