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Flatiron. Maximum subsidence (Sm) above panel centers is projected to range from 7.2 to 9.6 <br />~• feet (0.6t to 0.8t) beneath the canyons to about 6.0 to 8.4 feet (O.St to 0.7t) beneath areas of <br />greatest overburden depth. Maximum subsidence above chain pillazs (S~) is projected to range <br />from 1.2 to 3.6 feet (O.lt to 0.3t). <br />2. The third panel southwazd will be subcritical beneath Box Canyon based on width-to-depth <br />ratios [W/d] ranging from 0.5 to 1.1. Maximum subsidence is projected to range from as much <br />as 8.4 feet (0.7t) in areas of shallower overburden to about 6.O,feet (O.St) under deepest cover; <br />S~ is projected to range from 2.4 feet (0.2t) to as much as 4.8 feet (0.4t) in azeas of deepest <br />cover. <br />3. Panels 4 through 6 range from about critical to subcritical (W/d, = 1.3 to 0.5), assuming that the <br />chain pillazs support the overburden load. However, maximums subsidence is expected to range <br />from 3.6 to 7.2 feet (0.3t to 0.6t) because the subsidence factor above the chain pillars (S~) is <br />projected to range from 3.6 to 7.2 feet (0.3t to as much as 0.6t). Subsidence of as much as 7.2 <br />feet (0.6t) is therefore projected because the chain pillazs and caved material in the caved zone <br />(gob) aze projected to compress about equally. With the increased overburden loads under West <br />Flatiron and its flanking cliffs and steep slopes, these three southern panels are expected to <br />locally subside as a super panel (i.e., multiple panels and adjacent chain pillars that behave as a <br />single panel) of supercritical width beneath azeas of greatest overburden 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 wet <br />• mining conditions. This variance is expected because the final bulking factor of caved rocks <br />under dry conditions is greater than it is for caved rocks under wet conditions. <br />Maximum Tilt <br />Maximum tilt (Mm) 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 />(Sm/d in dimensionless units L/L). Tilt values at the West Elk Mine range from 0.014 to 0.021 <br />dimensionless units (L/L). Maximum calculated tilt ranges from about two to three times S,n/d (2 to <br />3 (5,,,/d)) at the West Elk Mine. Maximum filt in four different missing azeas of the Western United <br />States ranges from 2.5 to 5 (5,,,/d). <br />cache Rocks Mining Area -Based on analysis of the current West Elk Mine subsidence <br />monitoring network, and using an average value of 2.7 (5,,,/d), ;tilt above the eastern panels is <br />projected to range from about 0.006 in the southem 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 azeas to about 0.048 in the lower azeas of Horse Gulch: Following completion of E and <br />B-Seam mining, tilt is projected to range from about 0.033 on the higher ridges to 0.085 in Horse <br />Gulch. <br /> <br />2.05-117 March 1005PR/1 <br />~,~y, D~ <br />