Volume changes in grout used to fill up the tail void

Underground Space – the 4 th Dimension of Metropolises – Barták, Hrdina, Romancov & Zlámal (eds)
© 2007 Taylor & Francis Group, London, ISBN 978-0-415-40807-3
Volume changes in grout used to fill up the tail void
A. Bezuijen & W.H. van der Zon
GeoDelft, Delft, The Netherlands
ABSTRACT: Volume changes in grout to be applied in the tail void of a tunnel were measured in the laboratory.
Two different mechanisms that lead to volume changes have been distinguished: Bleeding of the grout, which
is the dominant mechanism when a tunnel is constructed in a permeable soil; and volume changes during the
hardening process. The last volume changes are the only volume changes that occur when a tunnel is constructed
in an impermeable soil.Two test set-ups have been developed to test these two different causes of volume changes.
It appeared that the volume changes caused by bleeding varied between 3 and 8%. Volume changes during the
hardening process were less than 3% for a two component grout that was tested. A 2-component grout mixture
with air appeared to have a certain elasticity also after hardening of the grout. As a result small volume changes
did not result in large pressure changes, which will lead to smaller loading on the lining compared with grout
without air.
1 INTRODUCTION
The tail void between the lining and the soil in a tunnel
is filled with grout during the construction of a tunnel.
This tail void grouting appears to be an important
process in tunnelling. This process appears to have an
important influence on the resulting settlement trough
and on the loading on the lining. Volume changes
in the grout after its application in the tail void will
lead to surface settlements above the tunnel and/or
will change the loading on the lining. Two different
mechanisms can lead to volume changes:
1. Bleeding of the grout. The water in the grout is
expelled to the surrounding soil when applied in
a permeable soil. The amount of bleeding depends
on the permeability of the grout, the consolidation
properties and the hardening properties.
2. The hardening of the grout. Even when there is no
bleeding, as will be the case when the tunnel is
bored in nearly impermeable soil as rock or clay,
volume changes can occur during the hardening of
the grout.
Two test set-ups have been developed to measure
the volume changes during bleeding and hardening of
grout.
This paper presents detailed information on the setups
and the results of various tests. Results will be
compared with small scale tests on samples with a
thickness of 0.02 m. Consequences for tunnelling will
be discussed.
389
2 SET-UP OF TESTS
2.1 Types of tests
Two different set-ups were used to test the volume
change caused by the two mechanisms mentioned
above for four different types of grout.
The first setup was a consolidation cell with a diameter
of 0.3 m in which a grout layer of 0.2 m thickness
was tested. The 0.2 m is comparable with the thickness
of a grout layer around a tunnel. This is important
because the ratio between hardening time and consolidation
time determines the bleeding. When the
hardening time is much less than the consolidation
time (for a layer of grout of a certain thickness) the
bleeding loss will be small. During a test the pressure
was kept constant and volume change was measured
continuously.
The second set-up was again a cell with a diameter
of 0.3 m and 0.2 m thickness. However, in this cell
there was no bleeding of the grout. The set-up was
designed to measure volume changes accurately. The
set-up was developed to see how a grout behaves that
is injected between the lining and the soil in the case
the surrounding soil is impermeable.
2.2 Bleeding tests
Tests have been performed to investigate the hardening
and bleeding of conventional grout, see Figure 1
and Figure 2. In this test a grout layer of 0.2 m is

air pressure
plate
grout
sand
d
Figure 1. Measurement principle.
Figure 2. Experimental setup.
valve
load
cell
water
collection
loaded mechanically with a constant load of 1–3 bar.
The expelled water is a measure of the consolidation
of the grout. After several minutes of consolidation
the sample was unloaded and the shear strength of
the grout was measured at different locations in the
grout. An example of results of such a test is shown
390
Weight expelled water (kg)
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
-0.2
350
300
250
200
150
100
0 10,000
Time (s)
-50
20,000
50
0
Applied air pressure (kPa)
Figure 3. Test result expelled water as a function of time
and applied pressure.
Height (cm)
20
18
16
14
12
10
8
6
4
2
10 min
20 min
30 min
0
0 2 4 6
Strength (kPa)
Figure 4. Strength development as measured with a vane.
in Figure 3 and Figure 4. Figure 4 shows the amount
of expelled pore water as a function of time and the
applied pressure. In this test a pressure of 300 kPa was
applied. Pressure was relieved several times to be able
to take the vane tests. Figure 4 shows the measured
shear strength after various times that pressure was
applied. In this test it was focused on the lower values
of the shear strength. Therefore only shear strengths
up to 6 kPa were measured and presented in the plot.
The type of grout tested here was tested before
at atmospheric pressure (Bezuijen et. al. 2002). In
that test it appeared that the measured shear strength
remained more or less constant until 5.5 hours and
after that time the hardening of the grout started.

airpressure
grout
plate
geotextile
0.2
valve
tot.press.gauge porepress.gauge
water
collection
Figure 5. Modified test set-up to measure the bleeding of
grout.
Comparing the result from the test at atmospheric
pressure with the results of the tests at 1–3 bar over
pressure it became clear that the increase in strength
in the over pressure case is caused by consolidation
of the grout and not by the hardening of the grout. To
understand the grout properties just after injection in
the tail void it is therefore necessary to understand consolidation.
If the grout layer is consolidated it will have
certain strength to act as a foundation for the tunnel lining,
even before hardening of the grout commences.
If it is not consolidated, it is possible that the shear
strength is too low to counterbalance the buoyancy
forces of the tunnel.Another important consequence of
consolidation is an increase of flow resistance, which
directly affects the pressure distribution behind the
TBM when drilling.
The vane test as shown in this Figure 4 was only
possible in case a grout was used with a relatively long
hardening and consolidation time. For tests performed
with two-component grout or grout without cement,
the strength development was not measured. For later
tests the set-up was changed, to avoid the preparation
of the sand sample and to be able to measure the pore
pressure and total pressure in the grout. The set-up for
these later tests is shown in Figure 5. The principle is
the same, but the drainage is in a different direction to
the top of the grout sample.
The test where evaluated using the theory developed
by Bolton & Mckinley (1997).There formulation written
in porosity changes in stead of void ratio (as in the
original paper) reads:
Where x is the thickness of the consolidated layer, ni
the initial porosity, ne the porosity after consolidation,
391
grout
plate
air
supply
total pressure
gauge
diff.
press.
gauge
membrane
0.2
pore pressure
gauge
Figure 6. Sketch test set-up, grout tests for rock applications.
k the permeability of the consolidated layer, �φ the
difference in piezometric head over the column and t
the time.
2.3 Measuring the volume changes in the grout
without bleeding
The test set-up for these tests is sketched in Figure 6.
The test set-up was designed to be able to exert a
constant pressure on the grout and to measure volume
changes accurately during hardening of the grout.
The pressure was kept constant by applying a constant
pressure at the air supply on top of the set-up.
An excess pressure of 1 bar was used during the tests.
Volume changes were measured by measuring volume
changes in the water cylinder on top of the container.

Table 1. Properties of the grout samples used.
Parameter CG 2CG NCG Dim.
Density 2109 1225 1840 Kg/m 3
water content. 16 225 36.3 %
D15 – – 0.0043 mm
D50 – – 0.017 mm
D85 – – 0.095 mm
Conf. pressure 300 100 100 kPa
Volume loss 8 3.5 4.5 %
Permeability cake 4.10 −8 1.3.10 −8 1.6.10 −7 m/s
A differential pressure gauge is attached to this cylinder
and a change in water level leads to a change in differential
pressure. Changes in the water level also lead
to pressure variations in the grout, but these variations
will be relatively small compared with the applied
excess pressure of 1 bar. The container with the grout
has an inside diameter of 0.284 m, the cylinder on top
a diameter of 0.03 m. The height of the tube was 1 m.
3 TESTS PERFORMED
3.1 Bleeding tests
Three different types of grout were tested. A ‘traditional’cement
based grout (CG), a 2-component grout
(2CG) and a grout mixture without cement (NCG) that
gets the desired properties by choosing the right grain
size distribution of the granular material in the grout.
The properties of the grouts selected and the volume
strains that were found in the consolidation tests are
summarized in Table 1. It should be noted that the volume
strain of the CG grout is higher than of the other
2 but that this was also measured with a higher confining
stress. For the same confining stress the difference
will be smaller.
As examples the results of the bleeding tests for 2CG
and NCG are shown in Figure 7 and Figure 8. These
materials were tested with the set-up of Figure 5. The
pressures are measured with the pressure transducers
in the plate below the grout. The vane tests were not
performed in these tests.
Although the 2 component grout has a certain
strength within a very short time (seconds) the volume
decrease due to bleeding continues until 5 hours
after the beginning of the test. In the hardening process
that starts after approximately 5 hours the pore
pressure decreases sharply until −100 kPa because the
water is bounded by the chemical reaction that leads
to hardening.
With the pressure applied (100 kPa) the bleeding of
the NCG grout is only present for a period of approximately
0.5 hour. Since there is no chemical hardening
reaction with the water the pore pressure decreases
until 0 kPa, but negative pressures are not found. The
392
Volume loss (%)
5.5
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
Volume loss
Pore pressure
Total pressure
0 5 10 15 20 25 30
Time (hours)
Figure 7. Result Bleeding test for the grout 2CG.
Volumeloss(%)
120
100
80
60
40
20
0
-20
-40
-60
-80
-100
5.0
110
4.5
100
4.0
90
3.5
80
3.0
70
2.5
Volume loss 60
2.0
1.5
Pore pressure
Total pressure
50
40
1.0
30
0.5
20
0.0
10
-0.5
0
0.0 0.1 0.2 0.3 0.4 0.5
Time(hours)
Figure 8. Result Bleeding test for the grout NCG.
Pressure (kPa)
measured pore pressure is not in agreement with the
theory of Bolton & McKinley (1997). According to
that theory the pore pressure should remain constant
at 100 kPa until all material is consolidated. During
the test it appears that the pore pressure at the bottom
of the sample already starts to decrease before the end
of consolidation, showing that the theory is only an
approximation of the real process.
The 2-component grout was also tested on bleeding
properties using a standard oedometer test with a sample
height of 0.02 m. In such a test the consolidation
times are theoretically 100 times shorter than in a sample
with a thickness of 0.2 m. Therefore the influence
of the hardening of the sample on the result will be less.
This resulted in a much larger volume loss of around
30%. This result shows that for grouts where the hardening
component is significant, the bleeding has to be
tested using a layer with a comparable thickness as is
expected in the application, thus for tail void grouts
this has to be the actual thickness of the tail void.
3.2 Results tests without bleeding
The tests without bleeding, with the set-up shown in
Figure 6, were only performed on grout type 2CG. One
Pressure (kPa)

Volume loss (%)
3.0
2.5
2.0
1.5
1.0
0.5
Vol.loss
Air pressure
Pore press.
Total press.
0.0
0 25 50 75 100 125 150
Time (hours)
200
150
100
50
0
-50
-100
Figure 9. Test volume change during hardening. 2CG without
air.
Volume loss (%)
3.5
3.0
2.5
2.0
140
120
100
1.5
60
Vol.corr (%)
1.0 Air press.
40
0.5
Pore press.
Total press.
20
0.0
0
0 20 40 60 80 100 120
Time (hours)
80
Pressure (kPa)
Pressure(kPa)
Figure 10. Test volume change during hardening. 2CG
with air.
sample with only 2CG and one sample where air was
mixed into the grout. Results are shown in Figure 10
and Figure 9.
Figure 9 shows the result without air. There is a
constant rate of volume loss until approximately 50
hours.After 50 hours the rate of volume loss decreases,
but even after 125 hours of testing the volume is still
not constant.The volume loss is then around 2.8%.The
experiment is stopped after 125 hours and the pressure
is released.This leads to a small decrease in the volume
loss. The results from the pore pressure gauge showed
again that during hardening of the grout all water is
used, leading to a very low pore water pressure.
The result with air, as shown in Figure 10, is different.
Now the pore water pressure remains positive. It
is likely that this is caused by the elastic storage that
is brought into the sample by the air. It appears that
even after 100 hours the grout has still some elasticity,
as can be seen when after nearly 100 hours of testing
the pressure is released resulting in a decrease of the
volume loss from 2.6 to 0.6%.
393
4 DISCUSSION ON THE RESULTS
The grout mixtures tested all appeared to have some
volume loss. This is caused by bleeding of the grout,
but also in the case bleeding is not possible during the
test there is a few percent of volume loss. The volume
loss will lead to a decrease in the pressure loading on
the lining in case the lining is placed in sand (Bezuijen
& Talmon, 2003). This means that the original stress
distribution in the sand is of no importance any more
when the tunnel is made, because this stress distribution
changes during the tunnel process itself (Bezuijen,
2006) and during the grouting process. Calculation
methods that use the original stress distribution will
over predict the loading on the tunnel, as was proven
by Hashimoto et al. (2002).
The 2CG was tested for the situation without bleeding.
This is the situation that can occur when the grout
is used in a rock tunnel or for a tunnel made in soft clay.
The 2.7 % volume loss will have not significant influence
on the pressure distribution of the soil around the
tunnel when this is soft clay, but may lead to considerable
pressure changes in case the tunnel is made in
rock, because both lining and surrounding (the rock)
will react very stiff. A situation where there is some
elasticity in the grout itself, as was the case for the
second test where the grout had 17% air, seems to be
advantageous. However, this will depend heavily on
the quality of the mixture, which is more difficult to
control when air is applied. Another advantage from
the air is that the density of the grout decreases, which
lead to a reduction in the buoyancy forces on the lining
(Bezuijen et al. 2005).
5 CONCLUSIONS
Bleeding characteristics of different grout mixtures
have been tested. Pressurizing these mixtures with a
constant pressure of 100 to 300 kPa led to a volume loss
of 3 to 8%. It was shown that these bleeding characteristics
can only be tested accurately in a setup where the
thickness of the grout layer is comparable to the thickness
of the layer that will be applied during tunneling.
Although in literature (see for example, Bolton and
McKinley, 1997) the bleeding process is described as
a kind of consolidation process only, it is a consolidation
process that is influenced by the hardening of the
grout. The time scale for consolidation is proportional
with the square of the thickness, but the hardening time
is independent from the dimensions.
The hardening leads to a large decrease in the
pore pressure in the grout. This can result in negative
pressures (relative to the atmospheric pressure).
In the tests without bleeding the presence of air
appears to have a remarkable influence on the results.
The grout mixture tested appeared to have an elastic

ehaviour even after 120 hours when the hardening of
the material is finished.
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bored tunnel, 2003, Proc ICOF 2003 Dundee.
394
Bezuijen A., Zon W.H. van der, Talmon A.M., 2005,
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