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• vulnerable to cascading pillar failure, a situation that arises when failure of one <br />pillaz transfers load to surrounding pillazs, causing wide-spread domino-like pillar <br />failure. Both the LAMODEL and UDEC modeling efforts support the validity of <br />the web and barzier pillaz design curves, and suggest that the roof, floor, and <br />interburden will remain stable. It should be noted, however, that the models were <br />not calibratedF~to field experience, but rather input parameters were based on <br />physical property data, experience, and engineetingjudgment. Until the designs <br />are validated in the field, caution should be exercised in their application. <br />• NSA's analyses indicate that highwall mining is geotechnically feasible for the <br />candidate seams in the Seneca IIW and Yoast Areas. The design curves <br />presented in Figures 34 and 35 provide Seneca Mine management with a <br />., rational starting point for highwall web and barrier pillar layout. By using <br />these curves to design panels as mining proceeds, and adjusting designs as <br />seam geometry and geologic conditions warrant, the likelihood of instabilities is <br />minimized. However, the seam dip exceeds the capabilities of the Peabody <br />Hgghwall Miner in several areas. Mining cross-dip and retrofitting the <br />machine with 60-in jacks help this situation considerably, but do not completely <br />eliminate it. In addition, the limited thickness of the Sage Creek Seam puts <br />further constraints on its minablility in light of the sidedips and the minimum <br />mining height of the PM. The lack of steering capability of the PM is a <br />• disadvantage under the seam conditions present. That is not to say that <br />highwall mining cannot be successful at Seneca with the PM, but in NSA's <br />opinion, the chances for success would be enhanced with a machine that has <br />guidance (position monitoring and steering) capabilities. <br />A <br />• <br />]V <br />