ENGINEERING GEOLOGY CONSIDERATIONS FOR SPECIFYING DAM FOUNDATION OBJECTIVES

INTRODUCTION
Dam foundation requirements are based on the type of
dam proposed and is largely dependent on the strength,
deformation, and permeability characteristics of site
materials. To determine the depth of excavation needed to
achieve an adequate foundation, observation of site
conditions in borings and test pits, field testing of soil
and rock, laboratory testing of representative samples and,
ultimately, design analysis is needed. A discussion of
site investigation techniques and the influence of geology
on dam design and construction are beyond the scope of this
paper. For a discussion of site investigation techniques
refer to Krynine and Judd (1957), Lowe and Zaccheo (1975),
Hunt (1984), and USBR (1987). Discussions of the influence
of geology on dams are found in Burnwell and Moneymaker
(1950), Legget (1962), Best (1984), Janson (1988), and
Goodman (1993). Janson (1983) provides a summary of the
kinds of geologically related problems dams experience, as
well as case histories of known dam failures.
This paper discusses various approaches for specifying
a foundation objective. The foundation objective is a
descriptive tool used to convey design intent information
to both construction engineering staff and the contractor.
The California Division of Safety of Dams generally
requires the specification of a foundation objective for
new dam projects. This paper illustrates the importance of
engineering geology in developing a foundation objective
that will be effective in controlling a dam foundation
excavation. The various approaches have been utilized in
dam construction practice observed by the author over the
past 13 years. A number of recent Northern California dam
projects, constructed under DSOD supervision, are presented
to illustrate the importance of engineering geology in
selecting an appropriate foundation objective approach.