INTRODUCTION
Request to Mine Beneath Bridge The Jakes Run Bridge is a reinforced portland concrete arch filled bridge located on WV Route 7 near Pentress, WV. The bridge has a span of 22.9 m (meters) and a height of 4 m above normal pool elevation to the underside of the center of the arch (See Fig 1). The bridge is a two lane structure with a width of 6.86 m. The structure is over 50 years old having been built in 1929 and is owned by the Department (WV Department of Highways). CONSOL (Consolidation Coal Company) is the owner of the mineral rights to the Pittsburgh Coal Seam under the subject structure, and had projected longwall mining under the bridge. They subsequently approached the Department with a proposal to mine beneath the bridge and determine the measures necessary to insure continuity of service and safety of the travelling public. The average height of mining in the coal seam was 2.47 m. The average depth from the surface to the bottom of the coal seam was approximately 140 m. The bridge structure was centrally located near the end of the longwall panel. The bridge was oriented on a skew of approximately 16 ° to the direction of mining. See Fig 2 for panel dimensions. Mining Method The long wall method was the system employed to mine beneath the structure and leaves no support for overlying strata. Because of this, rapid subsidence is normal immediately after mining. Longwall mining is highly desirable because of the high percentage of recovery, high productivity and conservation of resources.
EVALUATION OF THE SITE AND PROPOSAL
Agreement Conditions CONSOL performed an in-house engineering evaluation of the bridge. It was determined that the bridge could subside to the projected depths without critically damaging bridge or disrupting traffic. In May of 1982, CONSOL approached the Department concerning mining beneath the bridge. In June of 1982, the Department and CONSOL concluded an agreement which allowed miming under the structure. The agreement provided measures necessary to insure the safety and continuity of public travel on the bridge. The following are some of the significant conditions of the agreement: 1 - CONSOL was to install a support system comprised of beams and cribbing under the bridge that would subside with the structure and prevent any catastrophic failure. The contact points of the support were situated a few millimeters under the bridge so as not to impede the settlement of the structure. Approval by the Department was required for all protective measures. 2 - CONSOL was responsible for obtaining temporary detour easements and/or right of ways, and to provide a temporary creek crossing in the event the Department determined the bridge unsafe. The determination of the safety was to be the sole province of the Department. 3 - CONSOL was responsible for repair to the structure after subsidence was complete. 4 - CONSOL was to alleviate damage to the bridge by mining continuously so that the settlement process would be uninterrupted. CONSOL agreed to mine continuously within a distance of 21.34 m in advance of the nearest points of the structure to 33.5 m beyond the furthest point of the bridge.
