ABANDONED DEEP MINE SUBSIDENCE INVESTIGATION AND REMEDIAL DESIGN, INTERSTATE 70, GUERNSEY COUNTY, OHIO

A two thousand linear foot, undermined section oflnterstate 70 in Guernsey County, Ohio experienced settlements due to pothole type subsidence events within the travel lanes, shoulders and adjacent right-of-way areas.Potholes measured approximately ten feet in depth and width.The subsidence occurred after the dewatering of the abandoned deep mine during auger mining operations west of the site.A two-phase emergency investigation was undertaken by the Ohio Department of Transportation (ODOT) and Gannett Fleming Corddry & Carpenter (GF).The purpose of the investigation was to assess the immediate danger of potholes occurring in the traveled lanes and paved shoulders, to identify the subsidence mechanisms, and to design a remediation program.Phase one investigations involved the review of existing subsurface data, the advancement of shallow borings and the performance of multiple geophysical surveys including ground penetrating radar, seismic refraction and electromagnetic terrain conductivity.The Phase one investigations did not reveal the presence of subsidence voids.Phase two investigations included borings to the mine level and videotaping of mine conditions.The mine was found to be completely flooded.Based upon the collected data, two mechanisms of failure, localized roof fall and piping of overburden soils into the mine void, were identified.Two remedial alternatives, I) the filling of the mine void, and 2) the reinforcement of the highway using geotextiles, were evaluated.Filling of the mined interval and grouting of overburden bedrock fractures and voids, within a limited area, were selected.Construction plans, specifications and cost estimates were prepared for bidding and award.During the bidding process, a catastrophic, pothole type failure of the I-70 travel lanes occurred.The interstate was closed and the planned remediation activities were performed as an emergency project.The mine interval was grouted and portions of the highway pavement were replaced.The highway was reopened within 180 calendar days of the failure.