Semester

Fall

Date of Graduation

2012

Document Type

Thesis

Degree Type

MS

College

Statler College of Engineering and Mineral Resources

Department

Civil and Environmental Engineering

Committee Chair

John Quaranta

Committee Co-Chair

Joseph Donovan

Committee Member

Hema Siriwardane

Abstract

The coal mining industry has traditionally relied upon approaches that are principally based on US Bureau of Mines Information Circular (IC) 8741 by Babcock and Hooker (1977) for determining proximity distances and safety zones when mining under or near bodies of water. The proximity distance guidelines are limited by controlling the water inundation or seepage primarily for miners' safety. Since this initial work, research into mining under bodies of water has developed from subsidence studies performed by Kendorski (1993) and Bai et al. (1995). Recently, recovery of mineral reserves near bodies of water owned by the government is showing higher occurrence. In the USA, underground coal mining has affected surface bodies of water at public reservoirs and facilities owned or managed by the US Army Corps of Engineers. Lawsuits have become more numerous when detrimental effects of underground mining result. Such as in one case, damages in excess of {dollar}58 million were levied when the coal operator caused the failure of a dam necessitating the draining of a recreation lake (Hopey 2008). Most recently, the US Army Corps of Engineers and the US Department of Justice lost a federal lawsuit in Ohio to stop underground mining at a state park lake (Gray 2011).;Conventional factor of safety analysis methods and Empirical approaches to quantify offset distances for mining under surface bodies of water appear to be in question as they do not adequately support the assessment of risks essential for managing dams, flood systems, and projects (USACE 2008). The research presented here addresses the development of a tolerable risk guideline approach based on offset distances for longwall underground coal mining near surface bodies of water. This research involved identification of subsidence and seepage angles of draw that influence the likelihood of the progression of seepage erosion at the rim of a reservoir. A potential failure mode analysis was developed considering the likelihood and consequences of permeability changes in subsurface soils. An event tree analysis is proposed and formulated to include subsidence and seepage induced parameters based on literature reviews of field data. These event trees are linked to the conventional seepage failure events typically considered in risk analysis methods used by the US Army Corps of Engineers and Bureau of Reclamation. A sensitivity analysis is used to develop further insights in the estimated risk outcomes. For the ranges studied, the analysis determined that at a 200 ft (61.54 m) offset distance, a permeability increase will occur below the rim of a reservoir 78% of the time. As the offset distance increases to 600 ft (184.62m), the probability of increased permeability will reduce to 6%. The results show the probability that sub-surface erosion may occur from mining at distances far exceeding current offset guidelines recommended by Babcock and Hooker.

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