Mining Contract: Structural Analysis and Design of Seals for Coal Mine Safety
Seals are used to close off abandoned sections of the mine, ensuring that any explosions occurring in an abandoned part of the mine are contained and cannot reach parts of the active mine workings. It is critical that these seals are designed to withstand the high-pressure explosion transients experienced if an explosion occurs behind a sealed area.
Contract Status & Impact
This contract is complete and the final report is pending in 2014.
This contract was funded as part of an interagency agreement program, which provides a formal means for federal government agencies to share and further technology that could apply to and benefit mine safety and health. OMSHR identifies other government agencies with the knowledge, skills, and abilities relevant to a health and safety gap and works collaboratively with these agencies to identify the type of technology solution desired and to determine specifications for this technology.
This contract transferred protective structure design technology from the defense establishment to the design and construction of seals in the coal industry. Researchers at the US Army Engineer Research and Development Center (ERDC):
- modelled the structural dynamics of mine seals constructed with typical materials,
- developed an analysis tool for seal design based on wall analysis code (WAC),
- developed methods to protect seals from short-lived, high-pressure explosion transients, and
- recommended seal design guidelines based on design procedures developed for the Department of Defense.
These tasks were accomplished through the use of finite element analysis of typical seal designs under new explosion pressure requirements, and used past full-scale test data from NIOSH for model ventilation.
Three characteristics of coal mine seal design make it challenging and unique: the pressure-time curves specified for coal mine seal design by the Mine Safety and Health Administration (MSHA) (see the MSHA “Sealing of Abandoned Areas Single Source Page,” the “elasticity of design” requirement, and the seal foundation. An important protective structure design principle to apply in coal mine seal design is that a design should not fail suddenly in a catastrophic brittle mode, but should fail gradually in a ductile mode. For a seal structure to remain stationary, the seal foundation must provide sufficient anchorage capacity to resist shear forces developed from the design pressure-time curve. The preferred method to anchor a seal is with rock bolt anchors because their anchorage capacity is reliable and well understood.
Under this contract, a three-step design procedure for coal mine seals was presented that follows design codes and criteria developed by the military for design of protective structures. The procedure involves (1) design inputs where the design pressure-time curve, material properties, and seal geometry are specified, (2) foundation design where shear forces around the seal perimeter and the required seal anchorage are determined, and (3) seal structure design where the seal thickness and internal seal reinforcement are determined.
Design charts for these seal types were developed for the 830 kPa (120 psi) pressure-time curves with instantaneous rise time. The reinforced concrete designs in the chart are able to withstand a worst-case detonation wave; however, the designs are no longer elastic and permanent deformation occurs.