Environmental Engineering Reference
In-Depth Information
Concrete
dam
Drainage
gallery
A
B
Stilling basin
foundation
Concrete dam
foundation
Grout holes
Drain holes
(a)
Concrete
dam
Optional additional
concrete to below
low strength defect
Drainage
gallery
B'
B
A
Concrete dam
foundation to
below low
strength defect
stilling basin
foundation
Grout holes
(b)
Drain holes
Concrete
dam
Soil or weak
rock foundation
Contact
drain
A
B
A
B
key
key
(c)
Figure 17.2.
Foundation preparations for concrete gravity dams (a) conventional arrangement for dam
on rock foundation; (b) dam on rock foundation with low strength defect in foundation;
(c) dam with “keys”.
In general terms, after normal treatment by grouting and drainage, the rock founda-
tions must:
- Be of adequate strength, stiffness modulus and durability to support the dam loads, without
excessive deflections or settlements, under reservoir empty, full and all operating conditions;
- Have sufficient shear strength to provide an adequate factor of safety against sliding
downstream under all operating conditions;
- Be sufficiently impermeable and non-erodible to prevent excessive leakage beneath the dam;
- For dams with overfall spillways, or subject to overtopping during extreme flood
events, be able to withstand the impact of flood overflows at and near the toe, without
erosion which could endanger the dam.
For concrete gravity dams founded on soil (as many smaller dams and “weirs” are), the
requirements are essentially the same as for rock, but the foundations are weaker and
more compressible than rock, and are erodible, so the design must account for this.
