The Interaction of Active or Passive Roof Bolts, Stress Conditions, and the Immediate Roof Strata in a Longwall Mine in the United States

Author

Jonathan Richard Reisterer, Southern Illinois University CarbondaleFollow

Date of Award

8-1-2011

Degree Name

Master of Science

Department

Mining Engineering

First Advisor

Spearing, Sam

Abstract

Safety is the most important aspect to the mining industry. Research having a direct and positive impact on mine safety is always needed and should be supported. There are several different types of primary roof supports that are used to try to maintain stable mine workings in order to extract the coal safely. The majority of roof bolts installed annually in underground coal mines in the USA use resin cartridges (Tadolini, 2006). The standard roof bolt used is a fully grouted resin rebar bolt. This is considered a passive (un-tensioned) support. Technological advances in roof support anchored with resin grout systems have resulted in the development of supports that are active (tensioned during installation). Generally it is thought that active anchors are superior in performance as roof support except in highly laminated weak roof. The assumption is that since an active system applies some pre-tension to the roof, it will provide a more stable roof beam. There is, however, a lack of real data to back up this perception. A systematic attempt is through this project that addresses this knowledge gap. Without a clear idea on how different roof bolt systems work in-situ, the consequences could have a significant impact on the safety of the miners working underground as well as production costs. Supports are now often only chosen based on perceived ideas instead of real data. Such assumed superior performance of the support system could lead to false economy. Essentially, it needs to be demonstrated to what degree or under what conditions, if any, these technological advances in roof support improve ground conditions and opening stability and ultimately improve the safety of the miners. There is an argument regarding whether passive bolts could truly be better than active bolts. The focus is centralized towards a cost and performance issue. The overall goal of the proposed project was to develop an understanding of the interaction between different roof bolt types and the immediate strata in a longwall headgate as the longwall face progresses. In order to monitor the interactions between the strata and roof bolts, specially instrumented bolts were installed with six strain gauges that were electronically accessed. A look into the initial bolt loads was used to compare three different bolt types (both tensioned and untensioned) upon installation. These loads continued to be monitored and analyzed as the longwall face approached and passed the location of the instrumented bolts. Along with analyzing instrumented bolt data compared to a passing longwall face, a limited finite element model was set up within Flac3D to represent real conditions, and compare the in situ data collected to the computer outputs in order to establish beginning phases of validating the results.