Description;

 

The procedure to determine the factor of safety of slopes using the method of slices, with reference to Figureis as follows

Method of slices.

 

1. Draw the slope to scale and note the positions and magnitudes of any external loads.

2. Draw a trial slip surface and identify its point of rotation.

3. Draw the phreatic surface, if necessary.

4. If the soil is fi ne-grained, calculate the depth of the tension crack and sketch in a possible location of the tension crack. You can start at the crest and locate a point on your slip surface where the depth matches the depth of the tension crack.

5. Divide the soil mass above the slip surface into a convenient number of slices. More than fi ve slices are needed for most problems.

6. For each slice:

(a) Measure the width, bj.

(b) Determine Wj, which is the total weight of a slice including any external load. For example, for the two-layer soil profi le shown in Figure 16.10, the weight of slice   , where s1 and s2 denote soil layers 1 and 2, qs is the surface load per unit area, and za, zb, and zc are the mean heights.

(c) Measure the angle uj for each slice, or you can calculate it if you measure the length,
. The angle uj can be negative. Angles left of the center of rotation are negative.

For example, the value of u for slice 7 is negative, but for slice 2 , u is positive. Alternatively,  values of the slope of the slip surface in a slice give negative values of uj.

 

(d) Sketch an equipotential line starting from the intersection of the vertical center line and the slip surface to intersect the phreatic surface at ~908. The vertical projection of the equipotential line is the porewater pressure head, (zw)j.

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