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SURFACE SUBSIDENCE <br /> I I <br /> 90° <br /> eo° <br /> 70° <br /> 3)DIP <br /> kA <br /> W <br /> J <br /> 2 <br /> � 40° <br /> _ ad «1 SSE 1 <br /> J J l000 <br /> ?V ` <br /> 10° ` <br /> 100 200 300 400 SO° 600 700 Be 900 <br /> a ANGLE OF DIP OF SEAM <br /> Fig. 9.2.5 Effect of seam inclination on limit angles (12). Courtesy U.K. National Coal <br /> Board. <br /> that the time-dependent portion is much less than the instantaneous one <br /> and is sometimes so small that without a high-precision leveling instru- <br /> ment it is difficult to detect. This is best illustrated by the subsidence <br /> development curve in Fig.9.2.6(12),where the vertical axis is subsidence <br /> expressed as percentage of total subsidence and the horizontal axis de- <br /> notes face location. The curve indicates maximum subsidence at P as a <br />