ASSESSMENT OF THE PETROLOGIC, SEDIMENTOLOGIC, AND ENGINEERING CHARACTERISTICS OF THE DEVONIAN MILLBORO AND NEEDMORE SHALES, HIGHLAND COUNTY, VIRGINIA

Failure of shale strata due to poor engineering characteristics is a common occurrence in the Valley and Ridge Province of the Virginia Appalachians. Often, such failures result in sliding onto highways and require expensive slope remediation efforts. Combining petrologic and sedimentologic analyses with geotechnical techniques offers a useful strategy for investigating engineering characteristics of such materials. In this paper, we present a comparative study of the black, laminated Millboro Shale and the gray, bioturbated Needmore Shale, which are exposed along U.S. Route 250 in Highland County, Virginia. This study focuses on petrologic and sedimentologic analyses, including Scanning Electron Microscopy, thin section analysis, and bioturbation indices. Based on those properties, the Needmore Shale is hypothesized to be a stronger rock unit than the Millboro Shale. Direct shear tests and point load tests are used to evaluate the hypothesis. Stereonet analyses of discontinuity measurements taken from this outcrop are used as demonstrations of engineering behavior of the shale units.