PERMFILE58996

• Permit No: C1981034
• IBM Index Class Name: Permit File
• Doc Date: 11/3/1981
• Section_Exhibit Name: APPENDIX E Rocky Mtn Geotechnical - Additional Testing 11/3/81
• Media Type: D
• Archive: No

,~
Layer No. 3 is the thickest of the three roof units considered
in this analysis and is a sandstone. Once again, the friction rein-
forcement affects a decrease in bending stresses of 168 to 250. HOW-
ever, since the sandstone unit is the thickest and stiffest of the
three considered, the effect of suspension is to actually increase
the bending stresses in this stiff sandstone layer. The effect of
suspension is to increase the bending stresses by something on the
order of 350. The net effect of combined friction and suspension in
this layer is a slight increase in bending stress of from 28 to 158.
This same data has been represented in another form in Table
No. 3. This table indicates a factor of safety against failure for
each layer and each roof span condition, as well as indicating changes
in factor of safety for different types of roof reinforcement and
support. For purposes of this table, the factor of safety is defined
as the modulus of rupture for that material divided by the theoretical
bending stresses in that layer. In this table it may be seen that
for consideration of friction effects only, the lowest and thinnest
of the rock strata are associated with the lowest factors of safety.
The thin shale layer immediately above the coal, in fact, does indicate
a factor of safety less than 1, which would imply a failure condition.
In the case of suspension effects only, stress conditions are, in
effect, reversed. The highest factors of safety are associated with
the thinner lower strata which are now transferring stress into the
upper, thicker layer causing a substantial reduction in the factors
of safety there. This would imply that under the effects of suspension
only, failure would initiate in the sandstone layer well up into the
roof material. In realtiy, if a tension failure were to initiate in
this upper sandstone layer, we would not anticipate that any significant
7