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• 16 <br />oorditions. According bo Table 9, the angle of draw in Harvey Gap <br />area rocks can be estirtated at 25 degrees. <br />3.2 Calculatirn of the subsidence trough <br />The NGB Manual has been used for predicting the maximum sub- <br />siden~ based rn an assumption of potential pi]lar failures. fn thiti <br />assumption, certain factors have been taken into ~nsideratio~~, ~ar- <br />titularly: <br />1. Pillars may fail and the broken coal may fill up the avai~hle <br />space (rooms). <br />• 2. The overall development of the E seam is done in the torm ut , <br />"triangle" (Figure 4). Therefore, the subsidence li»e is ~i t~•rnurecl <br />in tNO cross-sections, section A-A at a distance ~ ~i 7_,UOI tee t in~i <br />section B 3 at a distance of 3,000 feet fran ttte t gal. <br />3. The surface subsidence is predicted for the level of 7,Ofi tex t <br />as a orniprcmise for the rugged mountain area. <br />3.2.1 Ground movFSnent in steep seams <br />The special trough shapes acoomlMrtying steep s~n~ t.~ve not <br />been much studied. Critical factors influencing the shap_ a ~.'i~ <br />subsidence line and the strain and slope values arE. sL-i11 unkno~rn. <br />• (Kratzsch, 1983). <br />