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• 2.3 Post Correction Factor of Safety <br />Using the pre-correction shear strength for soil strength and increasing the strength of the sliding <br />mass along 50 feet of the toe to simulate pins, the factor of safety was increased to about 1.3 for <br />the effective stress analysis and 1.23 for the total stress analysis. These factors of safety are <br />assumed to be the current factor of safety with just the pins in place. The other corrective <br />measures, such as the pond lining, stone columns, etc., are not taken into account with this <br />analysis. <br />2.4 Coefficient of Variation of the Shear Strength <br />Since the factor of safety is a function of the shear strength of the soil, a relationship between the <br />factor of safety and soil strength can be established. Figure 3 shows the relationship between the <br />factor of safety and the friction angle for the effective stress analysis, and Figure 4 shows the <br />relationship between the factor of safety and the undrained shear strength (assuming friction <br />angle is zero) for the total stress analysis. <br />The shear strength parameters are not precise numbers and are assumed to have a coefficient of <br />variation of 30 percent, based upon literature values and judgement (i.e., mean friction angle is <br />• 12.1 degrees but can vary from 8-47 degrees to 15.7 degrees, and the mean undrained shear <br />strength is 720 psf but can vary from 504 psf to 936 psfl. With these assumptions, the probability <br />of different strength values and factors of safety can be determined. For this analyses, the <br />probability is estimated upon a normal distribution of values. <br />2.5 Probability of Landslide Outcomes <br />The landslide outcomes are estimated based upon the factor of safety. A factor of safety of less <br />than 1.0 indicates failure and a rapid movement. A factor of safety between 1.0 and 1.2 suggests <br />that failure is incipient, tension cracks form, and movement is likely. A factor of safety between <br />1.2 and 1.5 is a value that is commonly used for temporary structures and suggests that movement <br />may or may not occur. A factor of safety of 1.5 is commonly used for permanent structures of <br />importance and suggests that no movement will occur. Therefore, using Figures 3 and 4, a shear <br />strength representing each of these landslide outcomes (based upon the factor of safety) can be <br />estimated, and the probability of the shear strength and corresponding factor of safety or landslide <br />outcome can be computed. <br /> <br />Os2so2a\so55s-UCET 3 <br />