Polygon Force Diagrams For Soil Mechanics

1.0 1.5 ' 2.0

(e) Determination of F

(e) Determination of F

(d) Full force diagram Fig. 5.31 Example 5.11.

The procedure starts by selecting suitable F values and evaluating the corresponding values for <j>m and cm:

For each value of F a polygon of forces for slice (1) is drawn and the force P obtained. Using this value for P the polygon of forces for wedge (2) is now drawn to give the total force diagram shown in Fig. 5.31c.

A typical set of calculations (for F = 2.0) is set out below.

Ti = 40 x 112 = 4480 kN (112 m is the base length of wedge 1) 28

As the directions of P and T2 are known, the value obtained for N2 will be correct. The error of closure, E, can therefore be assessed by comparing the value of T2 determined from the force diagram with the value calculated from N2 tan <i>m.

The force diagrams for the four chosen values for F are shown superimposed on each other in Fig. 5.3Id. The corresponding values of N2 and T2 are set out below.

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