Calibrating the LaModel Program for Shallow Cover Multiple-Seam Mines.

摘要

Stable underground mine openings are fundamental to ensuring the safety of miners and providing a safe work environment. During the past decade, approximately 40% of underground mining fatalities were caused by roof falls, rib collapses, or bumps/bursts, 19% of which occurred during retreat mining (Pappas and Mark, 2012). In addition, approximately 600 miners are non-fatally injured (often severely) every year by rock falls in coal mines (Pappas and Mark, 2012).;To help with designing stable mine pillars in deep-cover situations, a new calibration method for deep-cover pillar retreat mining was developed and implemented into the LaModel 3.0 program a few years ago (Heasley et al., 2010). This calibrated method was demonstrated to have very good results with a limited database of 47 deep-cover case histories, where a stability factor (SF) of 1.40 or above showed a 90% chance of success. During the development of the deep-cover calibration method for LaModel 3.0, there was nothing fundamental in the derivation that limited the method to only deep-cover mines; however, the method has not been specifically validated for shallow-cover mines.;This research work seeks to extend calibration of the LaModel program to shallow-cover mines. To perform this expansion, 40 shallow cover case histories from 12 different mines were obtained. The difficulty in finding shallow-cover failure cases for single seam mines necessitated creating a database which also included multiple-seam interactions. In general, with shallow cover, most mines were very successful, unless some type of multiple-seam stress became involved.;An initial analysis of the data showed two distinct failure populations, one comprised of inadequately sized pillars for global stability (mostly massive collapses) and one where local entry stability (massive roof falls or floor heave) was compromised by pillar stresses, weak roof/floor and/or multiple seam stresses. This distinction in failure mode required analyzing the database in two steps. First, an adequate pillar safety factor for global design stability was determined based on the pillar failure subset of the data. Then, once global stability was confirmed, the entry stability was analyzed separately to quantify the significance of parameters such as depth, coal mine roof rating (CMRR), entry stresses, etc. to the local stability of the entry.;Statistical analysis of the pillar failure subset of the data indicated that a SF of 2.0 or above resulted in an approximate 90% chance of maintaining global stability. Then, for the entry stability subset of the data, it was found that the CMRR and the multiple seam stress were most significant in predicting success or failure. With the addition of these two parameters, entry stability was able to be predicted with an approximate 75% accuracy.;Incorporating a shallow-cover, calibration technique into the LaModel program further enhances the most widely used boundary-element model to help develop stable pillar design at all depths. With the addition of this shallow-cover analysis tool, engineers can now perform basic pillar design where challenging geometries, multiple-seam interactions, and adverse geologic conditions are all considered.