Interface Behavior of Water Saturated Limestone Rock Joints Using Hollow Cylinder Testing and A Case History Regarding Mine Roof Stability: Fort Hartford Mine Superfund Site

Presented herein is a multi-part thesis prepared to partially meet the requirements for the Master of Science degree in Civil Engineering at the University of Tennessee. Part I provides a brief introduction to the two primary thesis topics that are presented in Parts II and III, respectively.

Part II presents findings from a series of tests performed with a hollow cylinder combined axial-torsional testing apparatus to study the effects of confining fluid pressure on the shear strength of artificial rock joints for Holston Limestone. Tests were performed for confining fluid pressures of 0.14 MPa to 0.55 MPa and effective joint normal stresses of 0.16 MPa to 0.65 MPa. Mohr-Coulomb failure criterion was used to interpret a joint effective friction angle for the Holston Limestone and the results were within the range of friction angle values given in published references. The combined effect of fluid pressure and mean stress on the joint interface shear strength was investigated for generalized stress conditions. It was found that an increase in intermediate principal stress resulted in measurable increases in joint interface shear strength, especially at lower normal stresses. Additionally, it was found that a simple linear relationship exists between the joint mean stress and the joint interface shear strength.

Part III is a case history regarding mine roof stability at the Fort Hartford Mine Superfund Site in Olaton, Kentucky. Specifically, mine roof instability at the Fort Hartford Mine Superfund Site has a number of potentially detrimental consequences including risks to mine personnel, subsidence damage, escape of hazardous gases from within mine, and contamination of the local groundwater system. Correspondingly, a study was performed in 1993 to delineate areas in the mine with low, moderate, and high potential for mine roof deterioration. During the study, a mine roof stability model was developed using map overlaying techniques, whereby the combined impact of key parameters were evaluated. Mine roof stability has been monitored at the site for the past ten years using both mechanical instrumentation and visual inspection. Intensive roof and rib scaling was performed, and mitigative measures were implemented to repair unstable roof at several locations within the mine. Based on a decade of supporting data, the mine roof stability model has been recognized as a reliable tool for developing in-mine transportation plans and mitigative measures.