M

MPw,Gk

© This value is obtained by integrating the equation for pore pressure given above, with a = 0m and d = 0.0001m . 0m. The subsequent value for the moment is obtained by integrating the same equation, having first multiplied by the distance from the toe.

© The destabilizing moment is the sum of the moments from the horizontal water thrust and the uplift beneath the dam.

© The stabilizing moment comes from the self-weight of the dam.

© The degree of utilization exceeds 100% and hence limit state EQU is not verified. The traditional lumped factor of safety against overturning in this case is between 1.12 and 1.19, depending on how that safety factor is calculated.

© This value is obtained by integrating the pore pressure equation, with a = 0m (sheet pile at heel) and d = 2m.

© The degree of utilization drops to 87% with the cutoff at the heel and limit state EQU is verified. The traditional lumped factor of safety is between 1.41 and 1.53.

© This value is obtained by integrating the pore pressure equation, with a = B (sheet pile at toe) and d = 2m.

® The degree of utilization rises to 121% with the cutoff at the toe and limit state EQU is once again not verified. The traditional lumped factor of safety is approximately 1.0.

7.7.3 Box caisson

Example 7.3 considers the design of the box caisson shown in Figure 7.13, which is sitting on a river bed and whose stability against uplift is purely a function of the caisson's weight and any uplift pressures from the water.

The purpose of this example is to consider how the UPL limit state is applied. In reality, the caisson would not sit directly on the river bed but be sunk into it. For simplicity in this example, the caisson is not buried.

(It could be argued that this worked example is not a geotechnical design situation, since it does not involve geotechnical parameters. However, box caissons usually appear in books on geotechnical engineering design, so we have included it for completeness.)

0 0

Post a comment