Laserfiche WebLink
West Etk Mrne <br />much as 8.4 feet (0.7t) in areas of shallower overburden to about 6.0 feet (O.St) under deepest <br />cover; Sro is projected to range from 2.4 feet (0.2t) to as much as 4.8 feet (0.4t) in areas of <br />deepest cover. <br />3. Panels 4 through 6 range from about critical to subcritical (W/d = 1.3 to 0.5), assuming that <br />the chain pillars support the overburden load. However, maximum subsidence is expected to <br />range from 3.6 to 7.2 feet (0.3t to 0.6t) because the subsidence factor above the chain pillazs <br />(SW) is projected to range from 3.6 to 7.2 feet (0.3t to as much as 0.6t). Subsidence of as <br />much as 7.2 feet (0.6t) is therefore projected because the chain pillars and caved material in <br />the caved zone (gob) are projected to compress about equally. With the increased overburden <br />]oads under West Flatiron and its flanking cliffs and steep slopes, these three southern panels <br />aze expected to locally subside as a super panel (i.e., multipke panels and adjacent chain pillazs <br />that behave as a single panel) of supercritical width beneath azeas of greatest overburden <br />depth. <br />4. The subsidence factor is projected to be less where the B-Seam roof rocks (sandstones, shales, <br />and siltstones) cave into dry mining conditions than it will be where the roof rocks cave into <br />wet mining conditions. This variance is expected because the final bulking factor of caved <br />rocks under dry conditions is greater than it is for caved rocks under wet conditions. <br />Maximum lilt <br />:, ~ Maximum tilt (M~ was calculated from differential vertical displacements at the West Elk Mine <br />monitoring network in terms of the ratio of maximum vertical displacement to overburden depth <br />(S,,,/d in dimensionless units L/L). Tilt values at the West Elk Mine range from 0.014 to 0.021 <br />dimensionless units (L/I.,). Maximum calculated tilt ranges from about two to three times Sin/d (2 <br />to 3~(Sm/d)) at the West Elk Mine. Maximum tilt in four different mining areas of the Western <br />United States ranges from 2.5 to 5 (S m1d). <br />Apache Rocks Mining Area -Based on analysis of the current West Elk Mine subsidence <br />monitoring network, and using an average value of 2.7 (Sin/d), tilt above the eastern panels is <br />projected to range from about 0.006 in the southern flank of West Flatiron to about 0.027 near the <br />head of Sylvester Gulch. <br />Tilt above the western panels, for E-Seam mining only, is projected to range from 0.017 on the <br />higher ridge areas to about 0.048 in the lower azeas of Horse Gulch. Following completion of E <br />and B-Seam mining, tilt is projected to range from about 0.033 on the higher ridges to 0.085 in <br />Horse Gulch. <br />Box Cann Mininr Area -Maximum tilt, based on analyses of West EIk Mine subsidence <br />measurements, is projected to range from 0.004 beneath West Flatiron to 0.035 above the <br />northernmost panel beneath Box Canyon. <br />2.05-117 RevisedJmnwryt998 PROS <br />