Environmental Engineering Reference
In-Depth Information
16.19 are shown on
Figure 16.8
. It can be seen there is a large scatter in the data and there
is a tendency towards over-estimation of the modulus. This needs to be considered when
using the equation.
16.4
STRENGTH OF THE CONCRETE IN THE DAM
16.4.1
What is recommended in guidelines
The tensile and shear strengths of the concrete in gravity dams is often taken from guide-
lines. Table 16.4 summarises the recommendations from ANCOLD (1991), CDSA (1999)
and FERC (2000).
It should be noted that these recommended values are used only where there is no ten-
sile or shear testing available.
16.4.2
Measured concrete strengths from some USA dams
16.4.2.1
Background to the data
Concrete strength test data for cores taken from 23 dams reported in EPR1 (1992) and
from test reports on 16 dams from USBR was analysed at UNSW (Khabbaz and Fell,
1999). The dams were all constructed by large, expert USA engineering organizations,
were in good condition, not showing signs of cracking, weakening of lift joints or serious
aggregate - alkali effects.
Three dams gave “outlier” data because they were affected by alkali aggregate reaction
or poor cement quality and these were excluded from the plots in
Figures 16.9
to
16.13
.
16.4.2.2
Tensile strength of concrete and lifts
larger diameter cores taken from the dams which had lift joints. Failure often occurred in
the concrete, not on the lift joint.
Table 16.4.
Summary of recommended tensile and shear strengths of concrete in dams.
Guideline and Recommended Value's (4)
Property
ANCOLD, (1991) (1)
CDSA, (1999) (2)
FERC (2000)
0.2
c
)
2/3
Static ultimate tensile strength
f
c
0.1
f
c
concrete
0.14(
f
0.05
f
c
lift joints
(3)
0.3
Dynamic ultimate tensile strength
f
c
0.17
Shear strength
0.14
f
c
f
c
concrete
0.085
- Peak
c
f
c
lift joints
0(5)
-Peak effective friction angle
45°
55° concrete
55°(5)
45° lift joints
Notes: (1) (a)
f
characteristic compressive strength of the concrete in MPa, usually at age 90 days
for new dams
(b) Values apply to “normal concrete with well prepared construction joints”. Lower values
apply for concrete of uncertain quality.
(2) Assumes good quality concrete and lift joints.
(3) Assumes intact concrete.
(4) Tensile and compressive strength, and cohesion in MPa.
(5) Assumes pre-cracked concrete.
c
