AN EXAMINATION OF THE LOYALHANNA LIMESTONE’S STRUCTURAL FEATURES AND THEIR IMPACT ON MINING AND GROUND CONTROL PRACTICES Anthony T. Iannacchione, Senior Scientist Paul R. Coyle, Geologist National Institute for Occupational Safety and Health Pittsburgh Research Laboratory Pittsburgh, Pennsylvania USA ABSTRACT (figure 1). These outcrops have historically been the sites for commercial aggregate mining, especially those closest to the A close look at the Loyalhanna Limestone of southwestern population centers in and around Pittsburgh, Pennsylvania. Currently Pennsylvania reveals a complex structural environment. Most nine quarries mine the Loyalhanna through underground and surface exposures of the Loyalhanna occur along Chestnut Ridge and Laurel operations in Monongalia Co., West Virginia, and Fayette and Hill within the Allegheny Mountain Section of the Appalachian Westmoreland Counties, Pennsylvania, (table 1) along the linear trace Plateaus Province. Because the Loyalhanna is rated as a super- of Chestnut Ridge. pavement aggregate by the Pennsylvania Department of Transportation and because of its proximity to the population centers of southwestern Pennsylvania, the Loyalhanna has been extensively Pittsburgh mined along these prominent anticlinal structures. Blairsville KEY Pennsylvania Latrobe Geologic and engineering analyses were performed using gas well Study Area and core logs, outcrop examinations, underground observations, and on mine maps. Strata exposures from both outcrops and quarries were Laurel Hill Anticline Mount Allegheny Front Section used to construct geologic maps, stereonet, and rose diagram Pleasant A projections so that the Loyalhanna’s structural environment could be understood better. Many of these structural conditions cause ground Connellsville Chestnut Ridge Anticline control problems at local quarries. These problems ranged from Uniontown N Appalachian Mountain Secti small-to-moderate sized rock falls associated with roof jointing to 0 5 Pittsburgh Low Plateau Section pillar failures associated with dipping discontinuities. Stresses ranged Allegheny Mountain Section B Scale, miles from tensional on structural domes where weathering dominates, to Pennsylvania Negro Mountain Anticline Pennsylvania high levels of compression within structural saddles. A greater West Virginia Maryland understanding of these characteristics is a prerequisite to develop A B Laurel engineering controls, such as improved mine layouts, pillar sizes, etc., ChestnutRidge Negro Mt. Ridge Front that lessen miner exposure to these hazards. Allegheny Loyalhanna Limestone INTRODUCTION Upper Salina Salt The Loyalhanna Limestone varies in composition from a Oriskany Sandstone (Major Decollement Surface) quartzose limestone to a calcareous quartz arenite (1). It underlies Figure 1. Location of major anticlinal structures and a generalized 17,000 square miles of West Virginia, Maryland, Pennsylvania, and cross-section through the Allegheny Mountain Section of the Ohio and averages 60 ft in thickness with a maximum thickness of Appalachian Plateaus Province. 103 ft (1). Wells (2) has since expanded the aerial extent of the Loyalhanna to Sullivan Co. in the northwestern portion of The Chestnut Ridge Anticline is a fold with limbs dipping away Pennsylvania. While this limestone is found under an extensive area from each other and, with erosion, exposes older geologic beds in four states and is a major source of crushed stone for southwestern nearest its central core. As this fold was produced in conjunction Pennsylvania, it has a limited area accessible to mining. The with the formation of the Appalachian Mountains, the rocks fractured Loyalhanna, which is typically greater than a thousand feet below the and broke to form joints and faults. Understanding the characteristics, surface in the Pittsburgh Low Plateau Section of the Appalachian such as orientation, dip, and spacing, of these structural features is Plateaus Province, crops out at numerous sites along the crest of necessary for mine design and development. Chestnut Ridge, Laurel Hill, and Negro Mountain Anticlines in the Allegheny Mountain Section of the Appalachian Plateaus Province Table 1. Quarries, strip mines, and road cuts visited during study These characteristics are also found in the 33 Loyalhanna caves along Chestnut Ridge. along Chestnut Ridge (3). In general, these caves are comprised of a single passage extending several hundred yards although a few are made up of extensive interconnecting passages, such as Laurel Letter Name County Site Characteristic Caverns and Bear Cave (Sites G and W, figure 2). Most of the caves A Buckeye Monongalia Surface quarry are found within two structural highs or domes along Chestnut Ridge B Laurel Fayette Surface quarry which are named after the gas fields they encompass, Summit and C Rt. 40 Fayette Road outcrop Griffin. In these areas the Loyalhanna has the greatest elevations and outcrop exposures, producing joints that are deeply weathered and, in Surface and D Coolsprings No. 1 Fayette many places, caves. underground quarry Surface and E Coolsprings No. 2 Fayette Mines along Chestnut Ridge have experienced roof and rib falls underground quarry with some falls resulting in injuries to mine workers. One quarry with Surface and a workforce of approximately 30-miners experienced 7-injuries from F Springfield Pike Fayette underground quarry ground falls over a 30-month period from March 1993, until September 1995 (table 2). A second mine had vehicles struck by Surface and G Rich Hill Fayette falling rocks approximately a dozen times during a 12-month period. underground quarry A third mine reported 9 roof falls to the Mine Safety and Health Surface and H Whitney Westmoreland Administration (MSHA) during an 18-month period from April 1999, underground quarry until November 2000 (4). Ground falls range in volume from boulder Underground size rocks, falling from the roof or rib, to massive roof falls measuring I Latrobe Westmoreland quarry 45 ft wide by 20 to 30 ft high and extending as far as 500 ft (figure 3). Surface and Many of the ground falls were, in part, due to the unique and complex J Torrance Westmoreland Underground structural environment of the Loyalhanna. The primary reason for quarry initiating this National Institute for Occupational Safety and Health (NIOSH) study is to increase knowledge of the root causes of these Abandoned coal K Bolivar Westmoreland hazards and promote the use of timely ground control measures so strip mine that miner safety can be improved. Table 2 - Roof fall injury data for one quarry from March, 1993, to September, 1995. Pittsburgh Date Injury Job Blairsville gg Caves cc ee & ff dd March 3, 1993 1 fatal injury Pumping a = Roades bb uw b = Smith's Ladder x, y & z (K) September 19, 1994 2 injured Drilling c = Barton t aa (J) s v d = Maybe-Nasty Latrobe October 25, 1994 1 injured Scaling e = Parva r f = Spider (I) December 28, 1994 1 injured Blasting g = Laurel p & q h = Franks May 25, 1995 1 injured Blasting i = Trout Hollow o (H) j = Jumonville August 23, 1995 1 injured Scaling k = Brooks Spring Mount Pleasant l & m = Casparis & Daniels n = Freeman Falls n o = Lycippus (A) Location of sites visited p & q = Flatfoot & Stone Knife r = Loyalhanna (G) s = Copperhead (F) Loyalhanna Limestone t = Spider Outcrop u = Con Connellsville Chestnut Ridge v = Evac l & m w = Bear Anticlinal axis x, y & z = Rattlesnake, Ken's & Bone k aa = Coon Uniontown bb = Lemon cc = Sawmill (D & E) dd = Tannery Hole j i N ee & ff = Torrance & Vex h gg = Strangford g 0 5 ef (C) d Scale, miles b (B) a c (A) Figure 2. Location of Loyalhanna Limestone outcrop, caves, and sites visited during this study. Capital letters A, B, D, E, F, G, H, I, and J are quarries; C is a highway outcrop; and K is an abandoned Figure 3. Massive roof fall measuring 45 ft wide by 20 to 30 coal strip mine. ft high and extending for approximately 200 hundred feet. Allegheny River Blacklick Creek N Loyalhanna River 5 1000 0 5 2000 1000 0 Scale, miles Conemaugh River Griffin Dome Loyalhanna Saddle 6 500 -500 0 Ligonier Uniontown 1500 Anticline axis Jacobs Creek Syncline axis 500 4 Youghiogheny River Jacobs Creek Saddle Monongahela River Structure contour 1000 1000 Chestnut Ridge 500 ft, interval 2 1500 3 Fault number and location 3 Ligonier Youghiogheny Cross-strike slip fault 1 Saddle (inferred) 1500 2500 0 2000 Strike thrust fault Uniontown Chestnut Ridge Summit Dome Dip 500 Ligonier Lineament (Gwinn, 1964) Figure 4. Structure contour map on the top of the Loyalhanna with major fold structures, surface faults, lineaments, and rivers and streams. THE STRUCTURE OF THE CHESTNUT RIDGE Major anticlinal folds within the Appalachian Plateaus Province ANTICLINE of Pennsylvania are generally arcuate convex to the northwest and parallel to the arc of the Central Appalachians. Structural relief on Chestnut Ridge is a large anticlinal fold which was formed as part anticlines decreases in step-like fashion northwestward in all parts of of the Appalachian Mountain system. This topographic feature is a the plateau (5). Chestnut Ridge is the last anticline in the northwest subdued structure in comparison to the intensely folded and faulted portion of the Allegheny Mountain Section with significant structural strata in the Valley and Ridge Province some 30 miles to the east. relief. The shape and character of the Chestnut Ridge Anticline was However, upon closer inspection, significant structures exist in the analyzed in past geologic reports by McElroy (6), Hickok and Moyer form of steeply dipping strata, thrust and slip faults, lineaments, and (7), and Shaffner (8, 9). In this study, a structure contour map on the a complex array of joints. All of these structures can present top of the Loyalhanna was prepared from oil and gas wells and localized hazards to miners. This factor is important since Chestnut limestone exploration drilling data (figure 4). The Loyalhanna was Ridge is southwestern Pennsylvania’s major source of high-quality found to rise from depths between sea level and 1,000 ft along the aggregate and miners will inevitably be exposed to these conditions Ligonier Syncline to heights between 1,500 and 2,700 ft along the as they do their work.