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Geotechnical News • September 2013
41
THE GROUT LINE
• τ=21.5
• t=103 min
The second professional selects 0.24
MPa and obtains:
• S=19.2 m
• δ=0.375
• ξ=0.625 for d=D
• ξ
r
=0.0016
• L=4.2 l/min
• τ=5.0
• t=32 min
The flow rate limit of the first profes-
sional is six times smaller than the
second one and the waiting time three
times longer.
Zero flow path
In a stage with multiple fractures, the
fracture with the largest thickness will
be grouted first. This hierarchy is a
well known fact. The split-spacing
sequence has long been used by practi-
tioners to grout the fractures with
the major thickness first, increasing
the excess pressure at every follow-
ing sequence. A sequential decrease
of grout consumption is generally
observed. If not, this may be due to
unexpected events or the use of an
inappropriate mix according to López-
Molina and Espinosa-Guillén [18].
The “Zero flow path” is the basic
concept that explains the hierarchi-
cal grouting sequence. Every fracture
has its own ZFP that delimits the rest
and advance phases of the grout in the
energy diagram. When the grout path
enters the rest phase, grout is immo-
bilised in that fracture. Grout is also
immobilised in fractures with smaller
thickness, even though the excess
pressure is not zero. It will continue to
flow in larger fractures.
Preliminary investigations are essen-
tial to identify the fractures and get
their ZFP. This is necessary to define
a grouting strategy and calculate the
correct flow rate limit at every stage
and sequence.
“
La Yesca
”
practice
The “La Yesca” practice is a tailored
methodology that was involved to dive
the grout curtains at the “La Yesca”
hydroelectric project in Western
Mexico [19,20]. It is based on recom-
mendations that were published in
the column of Grout Line [14] when
discussing the GIN target. And, for the
first time, ZFP was used in a grout-
ing project. Two energy levels were
selected to dilute the target. An active
grouting optimisation was considered
controlling alternatively the flow rate
and pressure steps to drive the grout-
ing path towards the target. Refusal
was asserted, depending on a feed-
back monitoring basis of the decreas-
ing trend of the grout consumption,
when penetrability lied between 1 and
5 l/min/bar. These values were prob-
ably selected based on field experience
since at that time the flow rate limit
was not yet parameterized.
Conclusions
Grouting without collecting data
on the geometry of fractures is no
more conceivable. The technological
advance changed the grouting and pre-
grouting data acquisition and eased
their representation in order to be anal-
ysed in the light of the new develop-
ments of grouting science.
The parameterisation of the flow rate
limit turned the “North American
Refusal Criterion” into an important
decision tool that will definitively
mark a new era of tailored and person-
alised grouting methodologies.
The “Zero Flow Path” is an essential
concept, which is used to get the right
grouting hierarchy and to calculate the
correct specific flow rate limit at every
stage and sequence.
The “Waiting Time” is a complemen-
tary tool where preference is given to
grouting at constant pressure.
The next challenge will be experi-
menting the new tools in field practice.
References
[1] López-Molina J.A. 2013.
Private
correspondence.
[2] Carter T.G., Dershowitz W.,
Shuttle D.A., Jefferies M.G. 2012.
Improved methods of design for
grouting fractured rock,
Proc. 4th
Int. Conf. Grouting and Deep Mix-
ing,
New Orleans, 1472-1483.
[3] Bonin G.R., Rombough V.T.,
Carter T.G. , Jefferies M.G. 2012.
Towards better injection control
and verification of rock grouting,
Proc. 4th Int. Conf. Grouting and
Deep Mixing
, New Orleans, 1460-
1471.
[4] Gustafson G., Stille H. 2005. Stop
criteria for cement grouting.
Fels-
bau
, 25, 3, 62-68.
[5] Kobayashi S. , Stille H. 2007.
Design for rock grouting based
on analysis of grout penetration.
Swedish Nuclear Fuel and Waste
Management Co
., Report R-07-13.
Stockholm. Sweden.
[6] Rafi J.Y., Stille H., Bagheri M.
2012.
Applying real time grout-
ing control method in sedimentary
rock. Proc. 4th Int. Conf. Grouting
and Deep Mixing
, New Orleans,
1450-1459.
[7] El Tani M. 2012. Grouting Rock
Fractures with cement Grout.
Rock
Mechanics and Rock Engineering
,
45, 547-561. Springer.
[8] Shuttle D., Rombough V., Bonin
G. 2007. GIN distilled,
Geotechni-
cal News
, 25, 3, 40-43.
[9] Bruce D.A. 2011. Rock grouting
for dams and the need to fight
regressive thinking.
Geotechnical
News
, 29, 2, 23-30.
[10] Bruce D.A. 2013. Refusal and
Closure in Rock Grouting: Let’s
Get it Right!
Geotechnical News
,
31, 2, 24-25.
[11] Lombardi G., Deere D.U. 1993.
Grouting design and control using
the GIN principle,
Water power
and dam construction
, June, 43, 6,
15-22.
[12] Lombardi G. 2011. Some con-
siderations on the GIN grouting
method.
Geotechnical News
, 29,
3, 25-28.