Geotechnical News September 2011
25
THE GROUTLINE
Grout Line
Paolo Gazzarrini
Overture
Here we are at the 25th issue of the
Grout Line and, as promised, Dr.
Lombardi’s answer to Dr. Bruce's
article, published in the June
2011 issue, has arrived quickly.
Following are the comments of Dr.
Lombardi (Studio Lombardi- Minusio-
)
Some Considerations on the GIN
Grouting Method
Introduction
In the recent paper titled “Rock
grouting for dams and the need to
fight regressive thinking” [1] Dr. Eng.
Donald A. Bruce presented some
general comments on the grouting
methods in use, subdividing them
into classes of “old”, “new” and
“regressive” methods or concepts.
Many
observations
that
he made are quite interest-
ing and can be entirely shared.
Others are difficult, if not impos-
sible, to understand and seem to
be based on a lack of informa-
tion or on some misunderstanding.
It is my feeling that a few comments
on these points are due and could be of
some interest. The comments will be
restricted to the pure grouting activity,
leaving aside the problems related to
the drilling methods.
On “Old” Methods
It can be entirely agreed that the
methods used in the USA from 1920
to 1980 - and in some cases also to the
present time - that is, since about the
time of the grouting of the Hoover dam
to today - should be finally changed.
The main points of these old meth-
ods are:
• the drilling of vertical holes to a tar-
get depth;
• the “one row” curtain;
• the relatively low grouting pressure;
• the use of “thin” mixes;
• the “thin to thick” mix grouting
method;
• the use of drillings of higher order
holes to sometimes “ridiculously
close centers”
• the use of thin mixes injected in
karstic cavities.
It is completely agreed that these
“old ways” contain major flaws and
have to be changed!
The “New” Method
The “new method used in the USA” is
claimed to have improved the grouting
procedure in a number of important
points. Mainly:
Montsalvens Dam (Canton Fribourg, Switzerland), built in 1920. One of the first
arch dams in Europe.
