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I• r ~ L_J • ARMA/USRMS 06-932 Subsidence Characteristics at Bowie Mines, Colorado Hamid Maleki Maleki Technologies, Inc., Spokane, Washington, USA Collin Stewart and Greg Hunt Bowie Resources, LLC, Paonia, Colorado, USA Copy}igh[ 2006, ARMA, American Rock Mechanla Assocafbn AR~I u This paper was prepared for presentation at Goitlan Rocks 2006, The 41st U.S. Symposium on Rock Mechaniw (USRMS):'S0 Veers of Rock Mechanics - LantlmaMa aM Future Challergesf, held in Goltlen, Cobrado, June 1]-21, 2006. TMs peperwaa selected torpresenta[bn by a USRMS Pmgram Committaefollowiigreview otinformation wmainetl in an abstraHaubmRed eadlerby Ne author(s). Comems of[hepeper, as presemetl, have rat been reviewed by ARMA/USRMS aiM are subjetl to carecton bythe author(s). The materiel, as presemetl, tlaes rat necessarily reflect any posRmn of USRMS, ARMA, Neir officers, or members. Elechonk repmtluction, tlisLibutan, or storage of any part of this paper for commerUal puryases wiNOUt [he written wnsem OI ARMAis prohibRed. Pennissbn to reproduce in prim is restricted 1o en abstraGOf not more Nan 300 woms; illustrationsmay rat be copied. The abstract mustmmain wnspicuous acknowledgement of where arM by whom the paper was presentetl. ABSTRACT: In this paper, the authors present areview ofdata-gathering programs and subsidence analyses in support of a mine permit. Using analyses of corehole and subsidence data, overburden deformation characteris[icsere addressed. It is shown that surface subsidence reaches a maximum of 2.3 m (7.5 ft) over the longwall panels. Subsidence is less than 0.06 m (02 ft) over the gate pillars at shallow cover azeas, but reaches 1.1 m (3.6 ft) under deeper cover. The amount of subsidence is influenced by variability in overburden thiclatesses and pillar designs adopted for the Upper D Seam. Ground movements are influenced significantly by topographic features. 1. INTRODUCTION Over the last decade, Bowie Resources, LLC (BRL), has been extracting coal reserves from the Upper D and B seams, located within the Somerset Coal Field near Paonia, Colorado. After extraction ofthe Upper D Seam reserves in the No. 2 Mine, BRL has recently initiated mining in the B Seam approxi- mately 90 m (300 ft) below the D Seam workings. The mine has employed the longwall mining method for the extraction of the Upper D Seam since 1999 using yield abutment gate pillar designs while monitoring both surface vertical and horizontal deformation with precision surveying techniques (GPS or Global Positioning Satellite Survey System) as shown in figure 1. In the gateroads of these longwall panels, BRL used yield abutment pillars while gradually increasing abutment pillar width from 30 m (98 fr) in the D3 headgate to 35 m (114 fr) in the DS headgate and beyond. Yield pillars were 11 m (37 fr) wide, and the longwall face was 250 m (824 fr) wide. Historic workings in the U.S. Steel Mine and the King Mine are also shown in figure I. Results have been analyzed on a routine basis to evaluate surface response over the panels and above the gate roads under the variable topographic conditions overlying the mine. Over the Upper D Seam reserves, the overburden ranges from few hundred to 426 m (1400 fr). The surface includes numerous deeply incised drainages at various orientations to the mine workings, and thus the influence of topographic conditions on ground movements has been of particular interest to this study. In addition to surface monitoring, BRL, in cooperation with MTI staff, implemented a geotechnical program consisting of drilling three continuous coreholes from the surface in one area, logging the depositional and stmctural characteris- tics of the core, geologic mapping, rock mechanics testing, and hydrologic monitoring. Overburden characteristics were evaluated using the Rock Mass Rating (RMR) system. Massive overburden units were identified capable of transferring loads and reducing differential movements for future extraction of the B Seam. A -1