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roach. A computerprogram was developed to solve the imensional equation <br /> presented in Tsur-Lavie, et al's analytical elasticity solution. This computer program is canabi <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 L,t x 4 x D); <br /> • The soil thickness over the void (T); and, _ <br /> • Poisson's ratio of the subsiding material. <br /> The computer program was verified by comparing its output with the characteristic curve <br /> presented in Tsur-Lavie, et. al's paper. <br /> Assumptions, 'Three basic assumptions were made to model the deformation of a surface du( <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; an( <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 sr <br /> e reduced by the arching effect of the material, i.e., waste, overlaying it. e ti%.-v.y, <br /> incorporating the waste above the liner could reduce the magnitude of the settlement by <br /> approximately half. <br /> Overburden <br /> �1 Clay <br /> Sand <br /> Cracks <br /> and Dropped <br /> rupture trapdoor Ruptures <br /> ,ro ae 1r0 +up<0 rro up loo+rr.>0 <br /> + + IX <br /> Inrtrat Sending Initial Sending <br /> stress stress stress stress <br /> Figure 2 Influence of overburden on lateral stress level <br /> (After Jessberger and Stone, 1991) <br /> I <br /> 1502-Vancouver,Canada-Geosynthadcs"93 <br />