ABSTRACT
Resisting Force The length of pier embedded in the stable zone should be sufficient to keep the pier being pulled out of the ground with a suitable factor of safety. If L2 is the length of the pier in the stable zone, the resisting force QR is the frictional resistance offered by the surface of the pier within the stable zone. We may write
(18.17)
where a = adhesion factor under compression loading
Cu = undrained unit cohesion of soil The value of a may be obtained from Fig. 17.15. Two cases of stability may be considered:
1. Without taking into account the dead load Q acting on the pier top, and using F s
= 1.2
(18.18a)
(18.18b)
2. By taking into account the dead load Qand using Fs = 2.0
QR(Qup -Q) = 2.0' For a given shaft diameter d equations (18.18a) and (18.18b) help to determine the length L2
of the pier in the stable zone. The one that gives the maximum length L2 should be used.
