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Geotechnical News • March 2016
THE GROUT LINE
these grouting results for rapid visual
interpretation by the site geotechnical
engineer.
For traditional curtain grouting in
rock there has been applied over many
years a simplistic rule of thumb for
reduction ratios between successive
phases of injection:
Grout absorptions per linear meter
for any phase should ideally lie within
the range of 25% to 75% of those for
the previous phase, indicating that the
curtain geometry, hole spacing, target
volumes, and grout mix are effective
and efficient.
Applying this criterion might in some
areas, if not for the whole curtain,
have led the Engineer to specify a
tertiary phase of treatment, at great
expense to the Client, or to change
unnecessarily the curtain geometry or
injection parameters. However, the
GIN technique, with observation of
the Equivalent Lugeon results, gave
the contractor and Client sufficient
confidence to halt the drilling and
grouting operations after the Second-
ary phase, and commencing the final
water testing programme.
Summary and Conclusion
The history of previous leakages at
Carno dam, the sensitivity of the
structure, the environmental and safety
requirements, and the necessity of
controlling project expenditure all
necessitated a careful and comprehen-
sive, but pragmatic approach to the
design and execution of the works.
Table 1: Numeric analysis for drilling and grout absorption.
Figure 6. Graphical plots of injection data.
