Semester

Summer

Date of Graduation

2009

Document Type

Dissertation

Degree Type

PhD

College

Statler College of Engineering and Mineral Resources

Department

Mining Engineering

Committee Chair

Syd S. Peng.

Abstract

The conventional 'full-scale' explosion test for seal evaluation is expensive and time consuming. Therefore, alternative methodologies must be developed for the design of mine seals to meet the new MSHA design standards. This dissertation employed advanced explicit finite element code, ABAQUS, to develop reinforced concrete (RC) seal models for addressing various design parameters related to the RC seal design.;Firstly, using back analysis of structural data available from NIOSH full-scale explosion tests on RC seals, a suitable RC seal model was developed with a proper concrete constitutive material. Secondly, the optimum rebar parameters such as rebar diameter, and vertical and horizontal spacing for reinforcing the concrete seal were determined. Thirdly, parametric analysis using the model with the optimum rebar parameters was performed. The parameters analyzed included entry height, entry width, surrounding rock strength, seal-rock/coal interface strength. A total of about 280 computer models were run. And finally, a RC seal design chart was developed for typical entry dimensions by analyzing the results of the numerical models.;Entry height is the dominating factor in RC seal design, whereas entry width has little effect. The tensile failure of concrete material on the outby surface of the seal dominates the seal failure mechanism. The reinforced steel rebars resist the high tensile stresses that may develop near the surface of the seal and prevent further tensile failure in the concrete material. It was also observed that simple tensile cracks in the concrete material on the surface of the seal do not significantly influence the overall stability of the seal. Various factors, such as, weighted average damage factor (WADF), tensile failure in the concrete, maximum lateral displacements, and axial forces in the steel rebars have been used to quantitatively assess the adequacy of the seal design.;This work also showed that various factors such as concrete constitutive behavior, roof-to-floor convergence, surrounding rock constitutive behavior, and explosion loading nature significantly influence the seal design. A very small amount of convergence on the seal could actually double the capacity of the seal, and this positive influence of convergence is valid only within certain limits. A weak surrounding rock deforms significantly under the rebar loading and could not provide sufficient anchorage for the seal, causing the concrete to fail extensively. It was shown in this dissertation that explosion pressures with instantaneous rise time and maintained for longer durations at peak values significantly influence the seal stability.

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