Geotechnical News June 2011
41
THE GROUTLINE
principles advocated by “old friends”
in the industry who are in fact typically
not grouting engineers by practice. A
classic example of this is the sporadic
emergence of the use of GIN Theory
as the guiding principle for curtain
grouting on certain U.S. projects.
Dr. Giovanni Lombardi is a Swiss
dam engineering expert who is an ex-
tremely influential figure, especially in
developing countries. His long associa-
tion with Dr. Don Deere, particularly
in projects involving curtain grouting
on South American dams, included the
development in the 1980’s of “GIN
Theory” (the GIN component refer-
ring to “Grouting Intensity Number”).
This was laudably developed to assure
for the client a certain standard of care
and quality would be achieved on proj-
ects which were in remote areas and/
or were to be built by contractors with
(somewhat) limited experience and ex-
pertise.
Together by 1993 they had articu-
lated an approach to grouting that takes
into account the specific energy ex-
pended in the injection process. Their
approach assumes that, for any given
interval, the energy expended is ap-
proximately equal to the product of the
final pressure (p) and the volume (V)
of grout that is injected. The numeri-
cal value of this product is called the
grouting intensity number, or GIN.
Depending on the units used, this num-
ber may be expressed in bar-liters per
meter. They recommended taking into
account site-specific factors, including
the ultimate reservoir head, the charac-
teristics of the bedrock discontinuities,
stratification, weak zones, weathering,
and in situ state of stress in selecting
a GIN number that — in conjunction
with limiting values of volume and
pressure — is to be used for easily
grouted fissures as well as for finer fis-
sures. They reasoned that because the
pressure decreases quite rapidly as the
grout moves away from the borehole in
tight fissures, the total uplift pressure
even at high injection pressures will as
a rule be much lower than the overbur-
den weight, except in the uppermost
5 to 10 m of the
foundation. On
that basis, they
indicated that a
limiting
pres-
sure as high as 50
bars might be ap-
propriate if high-
intensity grout-
ing were desired.
However,
for
most conditions,
they
recom-
mended using a
limiting pressure
of 30 bars and a
limiting volume
of 200 L/m.
Perhaps an-
ticipating objec-
tions to the grout
volume limita-
tion imposed by
the GIN rule,
Lombardi (2003)
stated that the
nominal limita-
tion could actu-
ally be treated as
a decision point
rather than as an absolute, rigid stop-
ping point. He suggested that the deci-
sion might be one of the following:
• Continue injection of grout.
• Terminate injection of grout.
• Temporarily stop grouting and re-
sume injection after a period of
time.
• Abandon the hole and drill another
nearby.
• Add a product, for example, an anti-
washout agent, to the grout mix, or
take some other appropriate mea-
sure
It would appear that application of the
GIN principle entails use of a single
“moderately thick” superplasticized
stable grout, defined in this case as a
grout with less than 5% bleed after 2
hours, throughout the injection process.
This grout is injected at a steady low to
moderate rate, allowing the pressure
to build up gradually as the grout
penetrates farther into the foundation
rock mass. Real-time monitoring of a
series of relationships or parameters by
computer graphics is required. These
relationships and parameters include
curves of pressure versus time, grout
flow rate versus time, total injected
volume versus time, and the derivative
curve of flow rate divided by pressure
versus time.
Lombardi and Deere (1993) stated
that the GIN principle had been used in
construction of grout curtains for dams
in Turkey, Mexico, Argentina, Austria,
Switzerland, and Ecuador. However,
Ewert (2003) vociferously pointed out
that application of the GIN principle
in certain geologic conditions and in
some rock types may be inappropriate,
especially if the grouting program is
in the hands of inexperienced person-
nel. His adverse opinions regarding the
GIN principle included the following:
• The maximum pressures proposed
by the principle are too high for
most rock types, causing hydro-
fracturing and unnecessarily large
grout takes.
• The maximum volumes allowed by
the principle when grouting at low
pressures are inadequate to ensure
complete filling of wider open
joints.
Photograph 3.
