2022-09-29_PERMIT FILE - C1980007 ‎(5)‎

• Permit No: C1980007
• IBM Index Class Name: Permit File
• Doc Date: 9/29/2022
• 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: No

Subsidence Evaluation for the
Exhibit 60E Southern Panels, Apache Rocks West, & Sunset Trail Mining Areas Page 5

831-032.923 Wright Water Engineers, Inc.
December 2021
3.0 FACTORS INFLUENCING SUBSIDENCE
Subsidence may be influenced by the local geology in the following ways:
1. Geologic structure. Attitude of the bedrock, faulting, and jointing may affect the mine layout
and mining method employed. In steeply dipping, faulted coal beds, for example, a mine layout
and method, such as room-and-pillar or limited panel-pillar, may be required. Joints often
control the way in which the roof rocks break, cave, and fracture, both underground and at the
surface during mining and subsidence. In relatively flat-lying, unfaulted coal seams like the
Southern Panels, Apache Rocks West, and Sunset Trail mining areas, there is latitude to
develop the most efficient layout and method to recover a maximum amount of the coal
resource with a minimum of impact.
2. Strength and behavioral properties of the rocks. These properties control the amount and rate
of subsidence. Strong, brittle sandstones and siltstones tend to break and cave in large blocks
on the mine floor. The bulking factor is greater for strong rocks than it is for soft, weak rocks.
The greater bulking factor of strong, caved material commonly reduces the height of caving
and the subsidence factor compared to soft, weak rocks. Conversely, the height of fracturing
often is greater for strong, brittle rocks than it is for soft, weak rocks.
3. Stratigraphic sequence. The stratigraphic distribution of rock units (stratigraphic sequence)
influences the effects of mining and subsidence. For example, strong and brittle sandstones in
the mine roof, as discussed above, can reduce the height of caving compared to shales, whereas
sandstones in the fractured zone above the caved zone may increase the height of fracturing
compared to shales. Conversely, the height of caving may be increased and the height of
fracturing decreased where weaker shale and claystones occur in the fractured zone above the
coal seam to be mined.
In addition, the lithology of the overburden rock may control the subsidence factor. The
subsidence factor may be less where the overburden contains a greater proportion of thick,
strong sandstones, and greater where the overburden contains thin, weak shales. In the
Southern Panels, Apache Rocks West, and Sunset Trail mining areas, the first 200 to 300 feet
of rocks above the E-seam consist primarily of siltstones, shales, claystones, local lenticular
sandstones, and coal seams.
4. Moisture content. Wet or saturated conditions in the mine roof and overburden tend to reduce
the bulking factor of the caved roof rocks. Therefore, the subsidence factor commonly is
greater under wet conditions than it is in dry conditions. In general, the greater the saturation
of the mine roof and overburden rocks, the greater the subsidence factor.