2021-02-05_PERMIT FILE - C1980007A ‎(5)‎

• Permit No: C1980007A
• IBM Index Class Name: Permit File
• Doc Date: 2/5/2021
• Doc Name: SUBSIDENCE EVALUATION
• Section_Exhibit Name: Exhibit 60E Subsidence Evaluation for the South of Divide and Dry Fork Mining Areas
• Media Type: D
• Archive: Yes

Subsidence Evaluation for the
Exhibit 60E Southern Panels, Apache Rocks West, & Sunset Trail Mining Areas Page 17
5.3.1.3 Maximum Horizontal Strain
Maximum positive horizontal strain (Em) measured at the West Elk Mine monitoring network
ranges between 1.1 and 1.4 times (Sm/d) (or 0.0058 and 0.0102-that is 0.58 and 1.0 percent);
maximum negative strain between-0.20 and-4.0 times (Sm/d) (or 0.0009 and 0.0307-0.09 to 3.0
percent)(Table 1). The range of horizontal tensile strain in four different mine areas of the Western
United States studied by Dunrud is 0.45 to 3 (Sm/d). The curves projected for tensile and
compressive strain in the Southern Panels mining area, based on the West Elk Mine monitoring
network and the National Coal Board of the United Kingdom, are shown in Figure 5.
Maximum tensile and compressive strain is significantly greater above large barrier pillars and
rigid chain pillars and mine boundaries than it is above longwall mining faces. This is because
tensile strains caused by mining the two adjacent panels are additive above the common rigid chain
pillars or unyielding mine panel boundary pillars. Cracks tend to be wider and deeper above barrier
pillars or the interface of mined and unmined coal at the limits of mining (e.g., mineable coal or
lease boundary) than chain pillars because of their greater rigidity (for example, the large tension
crack on the north side of Lone Pine Gulch).
The tensile strains obtained from the curves in Figure 5 are believed to be conservative for the
Southern Panels mining area. Maximum horizontal tensile strains, measured Dunrud in bedrock
during annual observations in the Apache Rocks West area (in hard brittle sandstone, where the
only strain is revealed by cracks), were 0.0031 to 0.0062 (0.31 to 0.62 percent). These values are
about 35 to 45 percent less than those shown in Table 1. The tensile strain is considered to be
close to a maximum value for those observed by Dunrud in the Apache Rocks West mining area
because 1)the features are located above the area if influence of a large solid coal pillar, and 2)no
greater strain was observed in the Apache Rocks West mining area.
Southern Panels Mining Area:
Maximum tensile and compressive horizontal strains are calculated,using the values obtained from
the area of the West Elk Mine, and as projected in Figure 5 (Table 2). These values are believed
to be conservative,based on Dunrud's annual observations in the Apache Rocks West mining area.
• Panels El to E9 and E14: For these panels, projected horizontal tensile strain ranges
from 0.005 to 0.027 (0.5 to 2.7 percent)where the planned coal extraction thickness is
9 feet, and from 0.007 to 0.042 (0.7 to 4.2 percent) where the extraction thickness
equals 14 feet.
Horizontal compressive strain ranges from-0.005 to-0.029(-0.5 to-2.9 percent)where
the extraction thickness equals 9 feet, and-0.007 to -0.045 (-0.7 to -4.5 percent)where
it equals 14 feet(Table 2).
• Panels B26 to B29: For these panels, projected horizontal tensile strain ranges from
0.004 to 0.017(0.4 to 1.7 percent)where the planned coal extraction thickness is 9 feet,
and from 0.007 to 0.026 (0.7 to 2.6 percent) where the extraction thickness equals 14
feet.
831-032.912 Wright Water Engineers, Inc.
December 2020