PERMFILE112504

• Permit No: C1981012
• IBM Index Class Name: Permit File
• Doc Date: 12/11/2001
• Section_Exhibit Name: EXHIBIT 24 SUBSIDENCE CONTROL PLAN
• Media Type: D
• Archive: No

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lam. f1.L Typical subsideoca JevdopoKnl curve (12). (:OUrte~Y U.K. National Cod
Bond.
function of the face location, which is advancing toward the right. Subsi-
dence at P begins when the face is O.7h ahead of P and increases linearly
as the face uJvunces. Subsidence accelerates when the face is about 0.3h
ahead of point P, reaching 15.5% of maximum when the face is directly
below P. It accelerates rapidly when the face passes beyond point P and
reaches 97.54'o when the face is O.7h beyond P. At this point active
subsidence is complete; the remaining 2 to 34YO is due to gradual compac-
tion of subsided ground and is known as residual subsidence or limo-
dependent subsidence. It should be noted that 0.7h is roughly one-halt We
critical width for the point P if the angle of draw is taken as 33•.
ResiJuat subsidence also occurs simultaneously with the instantaneous
subsidence. It can be measured by precise leveling or automatic photo-
graphic survey for various points along the subsidence curve. Figure 9.2.7
shows the instantaneous surface subsidence (solid line) and subsidence
prolilc (dusheJ line) 21 Jrys after the face stoppal. It is seen that
maximum residual subsidence of 9% occurs athalf-maximum subsidence
and that it decreases toward both ends, that is, the amount of residual
subsidence is proportional to the natc of subsidence of the surface points.
Residual subsidence is also associated with the physical properties of the
overlying straw. Strong rocks exhibit more residual subsidence than
weaker orres.
Thus we see that, according to the British investigatioru (12) limo-
dependent or residual subsidence can amount to a maximum of 94'0 0[ the
total subsidence if the face is stopped within the critics) widtb of the

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