Environmental Engineering Reference
In-Depth Information
1
Introduction
1.1
OUTLINE OF THE TOPIC
The topic sets out to present a state of practice of the geotechnical engineering of embank-
ment dams and their foundations and the geotechnical engineering of the foundations of
concrete dams.
It assumes that the reader is trained in Civil Engineering or Engineering Geology, with
knowledge of soil and rock mechanics.
There is an emphasis on the assessment of existing dams, as well as investigation, design
and construction of new dams. We have set out to give the background to design
methods, as well as the methods themselves, so the reader can develop a proper under-
standing of them. The topic is largely written about large dams, which ICOLD (1974)
define as:
Large Dam
: A dam which is more than 15 metres in height (measured from the lowest
point in the general foundations to the crest of the dam), or any dam between 10 metres and
15 metres in height which meets one of the following conditions:
-
the crest length is not less than 500 metres;
-
the capacity of the reservoir formed by the dam is not less than one million cubic
metres;
-
the maximum flood discharge dealt with by the dam is not less than 2000 cubic metres per
second;
-
the dam is of unusual design.
Three of the authors wrote “Geotechnical Engineering of Embankment Dams” (Fell,
MacGregor and Stapledon, 1992). This topic has some common elements with that topic but
has been extensively revised to reflect the current state of practice and the knowledge the
authors have gained since that topic was written, particularly about how existing dams
behave.
1.2
TYPES OF EMBANKMENT DAMS AND THEIR MAIN FEATURES
There are several types of embankment dam. The designs have varying degrees of in-built
conservatism, usually relating to the degree to which seepage within the dam is controlled
by provision of filters and drains, the use of free draining rockfill in the embankment and
the control of foundation seepage by grouting, drainage and cutoff construction.
Table 1.1
lists the common embankment dam zones and their functions. The zone num-
bering system shown is used throughout this topic. There is no universally adopted num-
bering system for zones in embankment dams. Some dams will have several rockfill zones
to accommodate the materials available from the quarry and excavations required for the
spillway.
Figures 1.1
and
1.2
show schematic cross sections of the most common types of embank-
ment dams now being constructed.
Figure 1.3
shows some earlier types of dams which are
