Project Background
Stark C&D Disposal is a licensed construction and demolition debris (C&DD) landfill located in East Canton, Stark County, Ohio. Surficial stratigraphy at the site consists of bedrock characterized by shale and sandstone members of the Allegheny Group interbedded with numerous coal, clay, and limestone beds. The numerous clay and coal beds are valuable resources in this area of Ohio. As such, they have been extensively mined in the county. At the Stark C&D Disposal site, The National Coal Mine Co. and NATCO Corporation mined the No. 6 or Middle Kittanning Coal until approximately 1915 and the Kittanning Fire Clay (mined for brickmaking) until around 1960. The No. 6 coal attains a thickness of 4 to 5 feet beneath the site, and the Kittanning Fire Clay, which lies approximately 30 feet below the No. 6 coal, reaches a thickness in excess of 10 feet. Both underground and surface contour mining techniques were utilized on site to retrieve the coal and clay. Due to these former mining operations, soils characterized as cut and fill and strip mine spoil occupy various portions of the site.
When the facility owners planned to expand operations, they contacted Bowser-Morner to assist them with the technical expertise in developing and implementing a program to stabilize the underground mines beneath the planned expansion areas as required by rule. The program had to meet the requirements of the portion of OAC 3745-400-07 which states that the recompacted soil liner for the landfill be constructed on a smooth surface that is capable of bearing the weight of the facility and related construction/operations without failure due to settling. With this in mind, Bowser-Morner developed a phased mine stabilization plan with the capability to expand as the facility expands.
Project Approach and Solutions
- Bowser-Morner conducted several preliminary investigations and public domain literature reviews for the facility to determine the extent and condition of the underlying abandoned mine works. The investigations consisted of using drilled borings in the planned expansion area. Combined ground penetrating radar (GPR) and very long frequency (VLF) electromagnetic (EM) technology was also utilized to gain a better understanding of the condition of the former mine works (intact or collapsed) and related rubble and to identify “anomalies” in the subsurface that may be associated with the overburden and bedrock including the presence of void spaces associated with karst or created as a result of the previous mining activities. A downhole camera was used as part of the initial subsurface study to further document the underground conditions. Boring logs and abandoned mine maps were obtained from the Ohio Department of Natural Resources (ODNR) to aid in determining the elevations and extent of the former mines.
- Utilizing the information obtained from the preliminary investigations and research, Bowser-Morner developed an Abandoned Mine Stabilization Plan.The plan detailed tasks and procedures for conducting appropriate grouting and stabilization of the underground mines in compliance with existing regulations.The developed methods employed at the site followed the “Standards of Safety” that are consistent with practices adopted by ODNR and the Ohio Department of Transportation (ODOT).
- Mine grouting activities began with layout of the grid for the grout borings on 25-foot centers, which was based upon previous recommendations and guidelines presented in USEPA and US Bureau of Mines documents for the reclamation of subsurface mining properties. The borings were advanced using an air-rotary drilling method since the high volumes of air forced down into the hole by this technique also serves to expel the drilled materials up and out of the borehole.A Bowser-Morner field geologist noted any potential void zones during boring activities.Grout was injected into the boreholes under pressure utilizing a ready mix that was specifically designed for the project by the supplier.The mix was ultimately selected to provide the best attributes based upon the typical void size, anticipated borehole “take”, presence of water in the void, and the supportive strength of the grout, as well as to reach the desired penetration and flow into the saturated former mine works.A Bowser-Morner concrete technician was on-site to observe the grouting activities and to document estimated grout intake quantities and measure the slump of each delivery of grout to ensure it met with the project specifications.The technician also collected a cylinder sample of grout per day of grouting activities.The accumulated samples were submitted to the Bowser-Morner Construction Materials Laboratory for seven-day and twenty-eight-day compressive strength testing in accordance with ASTM C1019.
- Stabilization of the former underground mines beneath the expansion area at the Stark C&D Disposal facility is an on-going process as the landfill expands. Several rounds of grouting of the known mine voids have been successfully completed to date. As a result, the mine stabilization program developed and implemented by Bowser-Morner for Stark C&D Disposal has been met with approval by the Ohio EPA as satisfying the requirements of OAC 3745-400-07.
