Environmental Engineering Reference
In-Depth Information
GROUT CURTAIN
GROUT CURTAIN
Figure 16.1.
Design loads on gravity spillway (adapted from ANCOLD, 1991).
H is taken here as the loads at maximum normal reservoir level, combined with the most
critical tailwater level, and H
F
is the load at maximum flood reservoir level based on the
inflow design flood (IDF) with corresponding water levels.
Internal water pressure and uplift
(
U
), which act within the rock foundation, at the
foundation-dam interface and within the body of the dam.
Static and dynamic thrust
(
I
), created by an ice sheet for reservoirs subject to freezing.
Silt and earth load
(
S
), vertical and horizontal loadings due to soil or rock backfill, and
from silt deposited against the structure.
Maximum design earthquake load
(
Q
)
.
Estimation of these loads is discussed below.
16.2.2
Load combinations
The following load combinations should be considered (adapted from CDSA, 1999).
Usual Loading.
Permanent and operating loads should be considered for both summer and
winter conditions including self-weight, ice, silt, earth pressure and the normal maximum
operating water level with appropriate uplift pressures and tailwater level (D
U).
Unusual Loading (blocked drains)
. Loads should be as for the usual loading case,
except that the drains should be assume inoperative (D
H
I
S
U
BD
).
Unusual Loading (post earthquake)
. If earthquake induced cracking is identified at the
rock-concrete interface or at any rock section in the dam or foundation, this may result in
altered uplift pressures and/or reduced strength of the concrete or foundation. A stability
analysis should be carried out to see whether the structure in its post-earthquake condi-
tion is still capable of resisting the usual loading (D
H
I
S
U
PQ
)
.
Concurrent ice loading should be considered in areas where appropriate. An inopera-
tive drain case assuming blocked drains should also be assessed and taken as an Unusual
Loading case. In some cases, e.g. where large displacements are expected at the dam-
foundation contact, this may be a highly likely condition.
Flood Loading.
Permanent and operating loads of the Usual Loading, except for ice
loading, should be considered in conjunction with reservoir and tailwater levels and uplift
resulting from the passage of the inflow Design Flood (IDF) (D
H
S
H
F
U
F
).
The effect of ice loads is not usually considered simultaneously with design flood
conditions.
S
