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Approach A computer.program was 'developed to solve the thee-dimensional <br /> presented in Tsur-Lavie et at s analytical elasticity solution. This computer pro �uati <br /> ' P P gram is.can <br /> Of evaluating the differential settlement caused by voids at depth. The input variables <br /> program consist of the following: <br /> • The void size (defined by Lk x 4 x D); <br /> • The soil thickness over the void (T); and, - <br /> • Poisson's ratio of the subsiding material. t <br /> The computer program was verified by comparing its output with the characteristic curve <br /> presented in Tsur-Lavie, et. al s paper. <br /> Assum tions Three basic assumptions were made to model the deformation of a surface due <br /> to the presence of a void at depth. These assumptions are as follows: <br /> • The liner surface is stress free; <br /> ® Differential settlement on a horizontal plane is projected to a graded surface; anc <br /> ® A constant Poisson's ratio. <br /> Each of the assumptions listed above is further discussed in the following sections. <br /> Stress Free Surface A stress free surface is one of the assumptions made in the solutior <br /> of the Elastic Model. This is a conservative assumption because the strains at the liner so- - <br /> are reduced by the arching effect of the material, i.e., waste, overlaying it. Mathemati,...-_.y, <br /> 0 <br /> incorporating the waste. above the liner could reduce the magnitude of the settlement by <br /> approximately half. <br /> OYe►bvrden <br /> clay <br /> Sano <br /> 72 <br /> cracks <br /> and sopped <br /> rvpIwe trapdoor Ruplwes <br /> ..o ..♦ ♦u,<0 uo rr. .ro r rre>O <br /> ♦ t t c <br /> Irtit/at Bendmq Initial 0endirg <br /> stress stress sire= stress <br /> Figure 2 Influence of overburden on lateral stress level <br /> (After Iessberger and Stone, 1991) <br /> • <br /> 1502-Vancouver,Canada-Geosynthtdcs'93 <br />