Entry roofs in underlying multiple seam mines are vulnerable to failure
under the influence of stress transferred from the upper seam workings.
Overburden depth, innerburden thickness, percentage of hard rock in the
innerburden and relative location of pillars in the two seams are some of the
factors known to influence stress transfer and ensuing instability in the
lower seam. This study was undertaken to quantify the effects of these
factors and to develop a comprehensive roof stability assessment model
capable of predicting any instability in the lower seam entry roofs under
given conditions of geology and loading.
The finite element analysis technique was used to model a range of loading conditions and innerburden lithology. The innerburden thickness was varied
from 50 to 20 feet. The innerburden lithology was varied in terms of
percentage of sandstone and its location in the innerburden. Various loading
conditions were simulated by changing the relative location of pillars in the
two seams and by varying overburden depths from 300 feet to 1500 feet.
Excessive horizontal stresses and unsymmetric loading were also simulated.
The effects of these factors were quantified in terms of safety factors across
the entry span.
next to an author's name indicates that all files or directories associated with their ETD are accessible from the Virginia Tech campus network only.
![[VT]](http://scholar.lib.vt.edu/images/ETD-db/restricted.gif)
