2011-02-14_PERMIT FILE - C1980007A ‎(3)‎

• Permit No: C1980007A
• IBM Index Class Name: Permit File
• Doc Date: 2/14/2011
• 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 South of Divide and Dry Fork Mining Areas Page 4
0 3.0 FACTORS INFLUENCING SUBSIDENCE
Subsidence may be influenced by the local geology in the following ways:
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 South of Divide and Dry Fork 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 over 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 South
of Divide and Dry Fork 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.
831 - 032.810 Wright Water Engineers, Inc.