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Subsidence Evaluation For <br />Exhibit 606 South of Divrde Mining An;a Page 9 <br />• thickness is 12 feet and from 1.4 feet (O.lt), where the extraction thickness is l4 <br />feet <br />2. Maximum subsidence is projected to range from 8.4 to 9.6 feet (0.7 to 0.8t), <br />where extraction thickness is 12 feet, and 9-8 to 11.2 feet (0.7 to 0-8t), where the <br />extraction thickness is 14 feet <br />5.3.1.2 Maximum Tilt <br />Maximum tilt (M~ was calculated from differential vertical displacements at the West Elk Mine <br />monitoring network in [eons of the ratio of maximum vertical displacement to overburden depth <br />(Sm/d in dimensionless units IJL.) (Table 1 and Figure 5). Tilt values at West Elk Mine range <br />tram I-4 to 2.l percent Maximum calculated tilt ranges from about two to three times Sm/d {2 to <br />3-(Sm/d)) at West Elk Mine. Maximum tilt in the South of Divide mining area is projected to <br />range from 2.2 to 2.3 Sm/d. Maximum tilt in four different mining areas studied by the author in <br />the Western United States ranges from 2.5 to 5-(Sm/d)- <br />South ofDivide Mining Area: As stated earlier in this report tilt above the eight longwall panels <br />(panels El to E8) and the single panel (E9) is projected to range between 2.2 and 23 Sm/d for <br />coal extraction thickness ranging between 8 and 14 feet These values are based on subsidence <br />measurements at West Elk Mine (Table 1, Figure 5). The overburden depth above the longwall <br />panel centers ranges from 400 to 1,425 feet (Table 2). <br />• • Panels El to E8: Maximum tilt in these panels is projected to range from 0.007 to 0-037 <br />(0.7 to 3.7 percent) where 8 feet of coal is extracted, from 0.013 to 0.044 (1.3 to 4-4 <br />percent) where 12 feet of coal is mined, and from 0.013 to 0.064 (13 to 6-4 percent) <br />where a 14-foot thickness of coal is mined (Table 2). <br />• Panel E9: Maximum tilt in this panel is predicted to range from 0.034 to 0.044 (3.4 <br />and 4.4 percent), where 12 feet of coal is mined and from 0.039 to 0.052 (3.9 to 5.2 <br />percent) where 14 feet of coal is produced. <br />5.3.1.3 Maximum Horizontal Strain <br />Maximum positive horizontal strain (E~ measured at the West Elk Mine monitoring network <br />ranges between 1.1 and 1.4 times (Sm/d) (or 0.0058 and 0.0102-that is 0.58 and 1.0 percent); <br />maximum negative strain between -020 and -4-0 times (Sm/d) (or 0.0009 and 0-0307.09 to <br />3.0 percent) (Table 1). The range of horizontal tensile strain in four different mine areas of the <br />Westem United States studied by the author is 0.45 to 3 (Sm/d). The curves projected for tensile <br />and compressive strain in the South of Divide mining area, based on the West Elk Monitoring <br />Network and the National Coal Board of the United Kingdom, are shown in Figure 5. <br />Maximum tensile and compressive strain is significantly greater above large barrier pillars and <br />rigid chain pillars and mine boundaries than it is above longwall mining faces. This is because <br />tensile strains caused by mining the two adjacent panels are addifive above the common rigid <br />• chain pillars or unyielding mine panel boundary pillars. Cracks tend to be wider and deeper <br />831-032-690 WiightWaterEngineers, lnc- <br />