Page 535 - Rock Mechanics For Underground Mining

CONTINUOUS SUBSIDENCE DUE TO THE MINING OF TABULAR OREBODIES

Figure 16.29 Profiles developed
over a series of longwall panels (after
Holla and Barclay, 2000).

Harmonic extraction involves the phased removal of the mineral from a critical
area such that the ground surface is lowered smoothly and horizontal strains are min-
imised. The technique may be used to protect structures that are especially important
or susceptible to subsidence-induced damage. Harmonic extraction requires that the
panel be advanced in at least two faces maintained at a carefully calculated distance
apart. The orientation of the structure with respect to the direction of face advance
determines whether protection against the transverse or the longitudinal surface wave
is the more important. Peng (1992) provides illustrations of harmonic extraction in
single and multi-seam mining, but indicates that the method is only applicable when
a single entry system between panels is used.

517