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Geotechnical News • December 2015
THE GROUT LINE
• application of a
single GIN value
,
the product Pressure x Volume,
which is constant for all stages
and boreholes, or (at least) all
stages within a given phase of
injection, and preferably for the
entire grout programme. The GIN
boundary curve defines the limits
within which injection should be
executed.
• application of
a rheologically
stable grout mix
whose design
and constituents is appropriate for
the rock conditions and desired
residual permeability.
• use of a
single
, rheologically
stable,
grout of low water-cement
ratio
. Without this, it is impos-
sible to compare grout absorptions
between different phases and
injection on a similar basis.
• establishment of a
maximum
injection pressure
.
• application of a
minimum effec-
tive flow rate
, the equivalent of a
refusal criteria, to terminate injec-
tions if injection flow rates become
too low to be practicable.
• establishment of
consistent injec-
tion parameters
for maximum
pressure, maximum volume, and
uniform injection rate up to the
point at which the GIN curve inter-
sects the GIN envelope boundary
curve.
• once the injection has reached the
boundary curve, a
progressive
reduction in the maximum pres-
sure
, following the GIN boundary
curve as the volume increases,
continuing up to the point at which
either maximum target volume, or
minimum flow rate, are recorded.
• estimation of the
target volume
,
based upon knowledge of the rock
formation and the required ground
treatment geometry
• plotting of results in the format of
an
Equivalent Lugeon
, provides
an indirect measurement which
allows an approximation of the
rock mass transmissivity with
water. This can provide a very
useful means of observing in real
time the progressive reduction in
permeability achieved by succes-
sive phases of grouting, and even
during an individual injection.
• execution of
test grouting
as
direct
unambiguous way
to confirm the
appropriateness of the mix design
and grouting parameters.
With the appropriate planning, equip-
ment, and control systems, GIN grout-
ing is very simple to apply in practice.
The function ‘Equivalent Lugeon’
has been recognised by many prac-
titioners. This function, calculated
on the basis of the ratio between the
viscosity of the grout and the viscos-
ity of water, is useful for tracking the
evolution of the injection, and the
progressive reduction in permeability
and transmissivity. It is noted that
Equivalent Lugeon is actually a rather
inappropriate and controversial name
for this parameter, and its use gives
rise to misunderstanding and resis-
tance amongst the grouting fraternity.
However, since this phrase is already
widely used, it is difficult to change its
name without generating confusion.
Establishing the GIN value
In general terms the GIN concept
helps to obtain the best grouting result
with minimum effort. The three under-
lying parameters to achieve this are
the grouting intensity number itself,
the maximum pressure and the maxi-
mum (target) volume. The GIN value
is the product of P, the injection pres-
sure, and V the cumulative volume. It
is a constant for any given injection,
so that the pressure decreases as the
injection progresses. The plot of this
function forms a limiting boundary
curve, (See Figure 11), which helps to
avoid a combination of high pressure
and high volume, which could have
the potential of damaging the rock for-
mation and risking surface heave. The
curve, plotted with P on the y axis,
and V on the x axis would at infinity
by asymptotic. The extent of the curve
is therefore limited by a cut-off at
P
max
( maximum allowable pressure ),
and a cut-off at V
max
( target injection
volume for the injection stage).
The definition, purpose, and the selec-
tion of appropriate values for the GIN,
P
max
and V
max
are discussed below.
GIN value
The choice of the proper grouting
intensity number (GIN) itself is based
on both, geological conditions as well
as on the project design and require-
ments.
Before addressing the determinant
geological factors, it needs to be noted
that the GIN concept has been specifi-
cally developed for, and is therefore
intended only for, fissure grouting.
Like for any other grouting method,
special attention must be paid to larger
voids, which should be filled with a
low mobility grout (LMG) or another
appropriate low cost material. This
confutes the sometimes still existing
misconception that GIN grouting is
generally not applicable in limestone.
In fact, numerous foundations com-
posed of fissured limestone have been
already successfully grouted using the
GIN technique. If local conditions,
such as the presence of large dissolu-
tion features often associated with this
type of rock, called for it, a corre-
sponding special treatment to fill these
voids was simply adopted.
As with the choice of the proper
grouting method, be it fissure grout-
ing or void filling, the selection of the
adequate GIN value depends on the
local site conditions and the expected
final result. Whether the purpose of
grouting is to reduce the permeability
of the rock mass or to strengthen the
foundation, the GIN value on a site
can be generally correlated to certain
geotechnical zones. Where a site is
characterized by highly variable rock
mass conditions distinguishing several
geotechnical zones, this might indicate
a need to apply different GIN values.
Generally, for rock masses of good
quality, a higher GIN value can be
used, whilst in weaker zones of lower
strength, grouting should be per-
