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-18- <br />• angle of 50 degrees, One of the best methods of evaluating the <br />available shear strength is to back calculate existing slopes. For <br />purposes of determinations of available shear strenyth, we assumed <br />that the previous excavations existed at a factor of safety near <br />1. In other words, the available shear strength nearly equalled <br />stresses imposed by the excavation. Various combinations of C and <br />6 were then used to evaluate the range of shear strength available <br />based on the previous excavation. <br />Analysis Methods <br />The methods of analysis used in evaluating the overall stability <br />of the slope and the stability of individual segments of the slope <br />included the graphical method of slices, a general method of slices <br />using a computer procedure, and chart solutions by methods based on <br />work done by Janbu and Taylor. To reduce man hours of engineering <br />it is most economical to search using the computer and check the <br />computer results using either the grahical method of slices or one of <br />the various chart solutions after the critical zones are located by <br />the computer search. The methods used in the computer are somewhat <br />more precise and yield computed factors of safety which generally are <br />10 to 15 percent greater than the less sophisticated methods. Design <br />to within 10 to 15 percent is not possible because shear strengths <br />are not known that closely for the slopes under consideration. Generally, <br />we used a circular search routine which searched the slope for critical <br />r~ <br />