Concrete gravity dams and their foundations - Geotechnical Engineering of Dams - page 684

Figure 16.20. Sliding friction shear strength of concrete-foundation contact - all USA dams data

(Khabhaz and Fell, 1999).

16.6 UPLIFT IN THE DAM FOUNDATION AND WITHIN THE DAM

16.6.1 What is recommended in guidelines

For new dams, or for assessing existing dams for which there are no measurements of pore
pressures in the rock foundations or on potential failure surfaces within the dam, there are
well-established empirical rules for estimating uplift pressures. Figures 16.21(a) and (b)
show the commonly used assumptions.
The pressures depend on whether the drainage gallery is above or below the tailwater
level and the efficiency of the drains.
For Figure 16.21(a):
For H4 TW

TW) (L

X)

(16.21)

H3 K (HW TW H4 H4

(L T)

and for H4 TW

TW) (L

X)

(16.22)

H3 K (HW TW

(L T)

where K (1 E); and E drain efficiency as a fraction.

For Figure 16.21(b):
For H4 TW

H3 K (HW H4) H4

(16.23)