26
Geotechnical News September 2011
THE GROUTLINE
• consideration of the importance of
the “pressure filtration coefficient”.
This coefficient corresponds essen-
tially to the old French “presso-
filtration”;
• use of various chemical admixtures
and not of water to the grout to
reduce the cohesion (and the vis-
cosity) of the mix, ensuring an en-
hanced penetrability;
• introduction of computer-based sys-
tems of monitoring the grouting;
• use of new methods of scrutinizing
the wall of the drill hole;
• “curtains must have at minimum 2
rows of holes”;
• use of inclined holes to upstream;
• declaring and measuring of the re-
sidual permeability;
• definition of a “stage refusal”.
In general one can share the prin-
ciples mentioned under this title, with,
however, a few comments which will
be presented later on.
The “Retrogressive Principles”
For sure, there are still existing cases
where old methods are used again, in
spite of the problems and flaws they
present. So e.g. the use of different
mixes from thin to thick.
On the contrary it is quite difficult,
or even impossible, to understand why
the GIN method is declared as “ret-
rogressive”. The following consider-
ations need to be made:
• The commentary that the GIN meth-
od was developed to “assure for the
client a certain standard of care and
quality … on projects … in remote
areas … or by contractors with lim-
ited experience and expertise” is
difficult to understand, unless one
considers, for example, Austria and
Switzerland as remote areas and
their contractors as having a lim-
ited experience and expertise!
• Since the GIN method theory was
first elaborated, it has been de-
clared that a grouting work should
be “designed” (engineered) not
“specified”. This appears now and
finally to be quite a “new” concept.
• From the beginning the GIN meth-
od has been based on the use of a
unique grout mix, the “best one”,
- obviously among the ones that are
available in practical terms - (cost,
availability of certain material and
so on). This is now claimed to be a
“new” concept.
• The definition of the best mix must
be based on two aspects: the “best
for grouting” and the “best for the
final result to be achieved”. There-
fore some compromises may be re-
quired in special cases. Obviously
throughout the decades the “best
mix” changes due to technologi-
cal progress (e.g. due to available
chemical admixtures), but this does
not change the principle of the GIN
method.
• The continuous monitoring and
representation of the data from the
grouting of any stage such as pres-
sure, flow rate, volume and penetra-
bility of the grout was always one
of the principles of the GIN-meth-
od. Obviously, the way to do it did
follow the continuous progresses of
the electronic equipment available.
In some of the new ones the GIN
value itself is directly shown on the
screen and all the required graphs
automatically produced. Now this
should also be considered a “new”
concept.
• Generally speaking, it is also clear
that some improvements were
implemented from time to time in
the GIN method, in order to keep it
continuously “new”.
• It is also felt that the definition of
a maximum pressure is unavoid-
able at least to define the pumping
equipment to be used. Thin is not a
“new” nor an “old” concept.
• The definition of a maximum take is
also to be considered necessary to
avoid excessive losses.
• In any case the three limits (maxi-
mum pressure, intensity and vol-
ume “limit”) must be the result of
previous grouting tests not values
arbitrarily “specified” a priori.
They should be changed if the
rock conditions are locally differ-
ent from the general assumptions
made.
• It was shown, by theoretical consid-
erations as well as by events during
grouting, that in given conditions
the hydro jacking is a function of
the “grouting intensity”, that is of
the energy pumped in at any stage.
The definition of a number GIN is
the logical consequence of this fact.
• By the way, it was always clearly
stated that the numerical values
indicated in the papers on GIN are
not “recommendations” but are just
“naming” for typical cases which
represent the average of a number
in particularly successful grouting
works. These statistics allow us to
recognize the type of grouting car-
ried out (low, medium, high, etc.).
In fact, it would be quite difficult
to recommend, at the same time,
an extremely low as well as an ex-
tremely high grouting intensity.
• It is well known that Prof. Ewert
doesn’t like the GIN method. In-
deed, when in certain cases the
grouting causes too many occur-
rences of hydro-fracturing, this
means simply that wrong values
were chosen by the user, often be-
cause the required preliminary tests
were not carried out.
• If he found that in certain cases the
volume limit is too low to fill the
voids of certain rocks, this means
again that the limit selected was
too low, maybe for the same or any
other reason. In any case, the GIN
method is not intended to fill karst-
ic cavities!
• Indeed, these and other misunder-
standings of the GIN method are
due to the fact that many people are
mostly looking for fixed norms and
specifications and are not very in-
terested in understanding ideas and
concepts.
• Furthermore, the basic idea of the
GIN, in limiting the intensity (p•V),
is to allow high pressure in order
to increase the reach of the grout
where the penetrability and thus the
take are low and, at the same time,
to eliminate - or at least reduce -
the cases of hydro-jacking when
the take at low pressure is too high.
It must be repeated that the risk of
hydro-jacking is the highest by the
combination of high pressure with
high take. Should the hydro-frac-
turing (indeed hydro-jacking) still
be too frequent, then the GIN value
