Geotechnical News • December 2015
49
THE GROUT LINE
This is why water pressure tests do
actually not give any indication on
the actual grout takes to be expected.
The only reliable way to obtain
information on the actual groutability
is therefore by the grouting process
itself, which should show a conse-
quent pressure increase and volume
reduction from stage to stage. The
use of Equivalent Lugeon analyses
can substitute for pre-grout tests in a
given stage, and provide intermediate
data on the progress and effective-
ness of the grouting programme. For
the determination of the actual fissure
conditions, that is especially their
aperture with reference to the situa-
tion shown in figure 7, a complemen-
tary inspection by a borehole camera
provides important information and is
therefore highly recommended.
With the GIN
method it is not
the Engineer that
defines the final
pressure, but it is
the rock, with its
localized (stage)
fissured status that
decides what will
be the final
pressure to be
reached.
Therefore, water pressure tests before
and again after grouting the grouting
programme, are allowed and even
recommended, in order to evaluate
the success of the performed injection
works, in terms of the final permeabil-
ity conditions achieved. To give a true
indication of the residual rock mass
permeability, post and pre-injection
water tests must be executed at signifi-
cantly lower pressures (normally equal
to the predicted groundwater pressures
in service) than the grouting pressures.
Failure to follow this procedure will
mean that the water tests will effec-
tively be testing fissures which have
not been affected by the grouting, and
at pressures exceeding the service
groundwater head, rendering the
results un-representative.
In the upcoming Groutline issue
(March 2016), the successful imple-
mentation of GIN grouting and other
above mentioned design concepts
in several challenging cases will be
presented.
Clif Kettle
Technical Manager, Bachy
Soletanche Ltd.,
Burscough, Lancashire, UK.
Maren Katterbach
Project Engineer, Lombardi
Engineering Ltd.,
Minusio, Switzerland
As promised, below, some of my com-
ments, as a strong supporter of the
GIN method.
Being Europeans the authors of this
articles, I think they didn’t, in my
opinion and correctly from their point
of view, emphasize a very important
point about the GIN method that,
again in my opinion, is essential. With
the GIN it is possible to use higher
grouting pressures than the grout-
ing pressures normally used in North
America. Also today, and for impor-
tant projects, I am reading Grouting
Specifications where the grouting
pressures are still evaluated with the
“infamous” (in my opinion) “Rule-
of-thumb” of 1 psi/ft (23 KPa/meter).
Parenthesis. [Talking one moment
about the “Rule-of-Thumb” (expres-
sion still used in our industry), my
question is; how Engineers, as we are,
can use a “rule-of-thumb” criteria?
Are we Engineers or magicians? With
all the respect for the magician. Will
you be comfortable going to the 54
th
floor of a high rise building built by a
structural engineer with rule-of thumb
criteria?]. Close parenthesis.
With the GIN method it is not the
Engineer that defines the final pres-
sure, but it is the rock, with its local-
ized (stage) fissured status that decides
what will be the final pressure to be
reached.
The article gives, additionally, a good
approach to use and values of what
should be the “consistency” of grout-
ing flow.
Another point that I would like to
emphasize is that with the GIN method
we can have a better characterization
of the status of the rock mass keeping
constant as many parameters as we
can; specifically flow and grout mix.
We avoid consequently, for instance,
fictitious “termination criteria” due to
change of grout mix, thicker.
Interesting to hear some comments
also from you, if any!
As usual, I make the same request,
asking you to send me your grouting
comments or grouting stories or case
histories. My coordinates remain:
Paolo Gazzarrini,
or
Ciao! Cheers!
