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r--, <br /> { 9.4 Ul-MRMINATION OF TROUGH SUBSIDENCE 305 <br /> —fi <br /> • <br /> ` B —f$ • <br /> fi ♦% I s I ,•� <br /> I � <br /> ` I I <br /> •% F•--- w <br /> Ae A� <br /> f <br /> Fig. 9A.7 Superposition of two critical profiles(20). <br /> i <br /> ithe maximum subsidence is at x s —}w, where <br /> S = S.. tan(w/B) (9.4.5) <br /> Influence Functions. The method of influence function or face element <br /> principles as defined by Salamon(16) considers an excavated opening to <br /> be composed of an infinite number of small openings or elements. Each <br /> small opening produces an individual surface subsidence profile,and their <br /> i summation is the total subsidence trough (Fig. 9.4.8). The influence is <br /> maximum when an element is directly below the surface point being <br /> I considered. It becomes minimum when the element is near the edge. <br /> Influence function <br /> i P Surface <br /> i <br /> I T I <br /> 1 1 1 1 1 1 1 1 1 1 1 <br /> I I I I I I I I I Trough <br /> I I I I I I I I I I <br /> 4 j 1 1 1 I I I <br /> I I ( I 1 1 1 1 1 1 1 1 <br /> I I I I I I I I I I I I <br /> I I I I I ( 1 1 1 1 1 1 <br /> Eptracthon elemental' <br /> Seam Goaf Seam <br /> Fib. 9AJ Superposition of infinitesimal influences(20). <br /> I <br /> I <br />