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A-1 <br />APPENDIX A <br />STABILITY ANALYSES <br />Stability analyses have been performed using the com- <br />puter program.STABL. This is an extremely flexible program <br />developed, by the School of Civil Engineering at Purdue Uni- <br />versity for the Indiana State Highway Commission. The program <br />performs stability analyses by the Simplified Janbu PQethod <br />for non-circular failure surfaces, and by the Simplified <br />Bishop Method for circular failure surfaces. All failure <br />surfaces were assumed to be circular for our analyses. <br />The Simplified Bishop,Method is a method of slices in <br />which the failure mass is divided into a number of vertical <br />slices to estimate the stress distribution along the failure <br />surface. In order to reduce the number of unknowns to the <br />number of equations of equilibrium, the assumption is made <br />that vertical side forces on each slice are zero. Forces are <br />then resolved in the vertical direction, eliminating the <br />side forces. The method satisfies overall moment and vertical <br />force equilibrium, but does not satisfy the moment equilibrium <br />of individual slices or horizontal force equilibrium. Forces <br />acting on each slice are determined so that the total driving <br />forces and resisting forces along the assumed failure surface <br />can be calculated. The safety factor is then defined as the <br />total resisting forces (shear strength) divided by the total <br />driving forces along the assumed failure surface (shear <br />stress required for equilibrium). The Simplified Bishop Method <br />has been found to produce highly accurate results over a wide <br />range of conditions. <br />Critical or minimum safety factors have been determined <br />for the sections analyzed by using an automatic search pro- <br />cedure. This involves specifying the lower (toe) and upper <br />(crest) regions of the slope within which the failure circle <br />c~rono ca+w~mw, iNC. <br />