Volume changes in grout used to fill up the tail void

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)