Conceptual-level Geotechnical Evaluation of Rock Mass Conditions for the 7400 Level Campus at DUSEL

摘要

A multi-disciplinary Deep Underground Science and Engineering Laboratory (DUSEL) is being planned at the site of the former Homestake Gold Mine in Lead, South Dakota. Current plans include development of large excavations at the 4850 (1480 m depth) and 7400 (2260 m depth) Levels. Proposed excavations at the 7400 Level include large excavations (15 m × 15 m × 75 m) and associated smaller facilities. The geology of the ore bodies at the former Homestake Mine is well understood, but the proposed DUSEL facilities are being developed away from the old mine workings where information is limited. A conceptuallevel characterization of the geological/geotechnical conditions anticipated to exist at the 7400 Level has been undertaken to form a basis for conceptual design of planned excavations. The characterization was based on a combination of (i) extrapolation of geotechnical and geological data from the 4850 Level, (ii) historic Homestake Mine data, and (iii) professional experience and judgment. The evaluation suggests amphibolites of the Yates Member of the Poorman Formation are likely most suitable for proposed excavations. A significant increase in in-situ stress (as compared to measured values at the 4850 Level) suggest the excavation of the 7400 Level campus may be affected by high stress conditions; ductile deformation in weaker rocks; and spalling or potential strain bursting in stronger rocks.