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Obviously there is a very wide range of shear strength values <br />which may be utilized in the analysis, depending upon assumptions made <br />with respect to existing conditions. We have attempted to determine <br />the relative effect of different assumptions with respect to shear <br />strength on the results of stability analysis. Our approach to the <br />analysis and justification for the assumptions made will be found in <br />the next section. <br />DESCRIPTION OF STRATA AND SLOPE MODEL: <br />In order to properly analyze the stability of the west portal <br />area it was first necessary to develop a mathematical and geometric <br />model of the slope conditions to be used for purposes of slope stabil- <br />ity analysis. The development of this model is described in this <br />section. <br />Information obtained from old topographic mapping in the west <br />portal area and from test boring information tend to indicate that <br />the existing cut in the high wall has not greatly altered the slope <br />condition from what would appear to have existed in the past. The <br />site is located at the outside of a meander bend in the North Fork <br />of the Gunnison River. This erosion activity at the toe of the very <br />steep slopes in the area is believed to be responsible for instigat- <br />ing the movement in the landslide complexes known to exist in this <br />area. The west portal facility is located within the limits of one <br />of these landslide complexes. The: visual appraisal of the existing <br />slope in the high wall area, exposing the silty clay soils containing <br />large cobble and boulder size debris, leaves one wondering how such a <br />cut slope could have remained stable for something well over two years. <br />However, at this time it would appear that the cut made in this area <br />-5- <br />