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ASSUMPTIONS <br />I. Both sliding surface and tension crack strike parallel to the slope surface. <br />2. The tension crack is vertical and is filled with water to a depth Zy~. <br />3. Water enters the sliding surface along the base of the tension crack and seeps <br />along the sliding surface, escaping of atmospheric pressure where the sliding <br />surface daylights in the slope face. <br />4. The forces W (the weight of the sliding block), U (uplift force due to water <br />pressure on the sliding surface) and V (force due to water pressure in.ihe tension <br />crack) all act through the centroid of the sliding mass. In other words, it is <br />assumed that there are no moments which would tend to cause rotation of the <br />.block and hence failure is by sliding only. <br /> 5. The shear strength of the sliding surface is defined by cohesion c and a fraction <br />• angle ~ which are related by the equation t c + Q tan ~ ` <br />6. A slice of unit thickness is considered and it is assumed That release surfaces are <br />present so that there is no resistance to sliding at the lateral boundaries of the <br />failure. <br />7. The unit weight of the material is 160 Ib/ft3 with o cohesion bf 30,000 Ib/f12. <br /> <br />Revised 3/82 3.5C-2 <br />