Environmental Engineering Reference
In-Depth Information
4
1
1
2A
2C
Cut-off
foundation
2B
General
foundation
General
foundation
Grout
curtain
(a)
EARTHFILL WITH VERTICAL AND HORIZONTAL DRAIN
2A
2B
3A
3B
3B
1
3B
4
2C
Grout
curtain
General
foundation
Cut-off
foundation
General
foundation
(b)
EARTH AND ROCKFILL - CENTRAL CORE
Concrete
face slab
2D
2E
3A
3B
Plinth
Grout
curtain
Cut-off
foundation
General
foundation
(c)
CONCRETE FACE ROCKFILL
Figure 17.1.
Terms used for foundation preparation for embankment dams (a) earthfill with vertical
and horizontal drains, (b) earth and rockfill (c) concrete face rockfill.
- Loads imposed on the foundation, and the strength and compressibility of the soil or
rock in dam foundations, allowing for the detailed geological structure, including bed-
ding, jointing, and the presence of shears and faults;
-Erodibility and permeability of the soil or rock in the dam foundation;
-Groundwater inflows to excavations;
- Climate, and river flows.
Figure 17.2
shows three arrangements for foundation preparation under concrete grav-
ity dams. Figure 17.2: (a) shows the conventional arrangement, where the foundation is
all taken to a uniform requirement; (b) shows the case where a low strength defect exists
in the rock (e.g. low strength bedding surface) and the foundation is taken below the
defect; (c) shows a foundation where “keys” have been used to take the critical failure sur-
face deeper into the foundation. “Keys” or cutoffs may be required to prevent undercut-
ting of the downstream toe by the spillway flow.
In each case A-B is prepared to concrete dam foundation standard (A-B
if the addi-
tional concrete in Figure 17.2(b) is required). A lesser standard may apply under the still-
ing basins or between the keys in Figure 17.2(c).
Grout holes and drainage holes are usually provided as shown in Figures 17.2(a) and (b) to
control uplift pressures beneath the dam. For smaller dams contact drains, as shown in Figure
17.2(c) have been used. These drains are ineffective except at possibly the foundation contact
as discussed in Chapter 16.
