10th Asian Regional Conference of IAEG (2015)

Influence of curing conditions on mechanical properties of chemically grouted sands andits micromechanism
Gailing ZHANG (1), Xun SUN (2) and Yankun LIANG (1)(1) School of Resources and Geosciences, China University of Mining and Technology, China
E-mail: gailing-zhang@cumt.edu.cn(2) China University of Mining & Technology (Beijing), China
Abstract
This paper presents an investigation of the influence of different curing conditions on
the mechanical properties of chemically grouted sands by using laboratory experiment andmicroscopic techniques. The orthogonal experiment shows that slurry concentration has
more influence on unconfined compressive strength of chemically grouted sands. Curing
period is main effect on the permeability. Slurry concentration has a greater impact oncohesion and temperature has more impact on the internal friction angle. The results ofmercury porosimetry show that the porosity decreases with increasing chemical grout slurry
concentration. The porosity of most chemically grouted sands substantially equals to or
greater than that of the samples before the compression test. The porosity of different
chemically grouted sands is different due to the different concentration of grout, which has
important influence on the permeability.

Keywords: chemically grouted sands; curing conditions; mechanical properties; mercury
porosimetry
1.

Introduction

and chemical grouts.
A coarse sand (C.S) (particle size lager than 0.5mm accounted for over 50% weights) according toclassification standard of soil (GBJ145-90), wasselected, and its particle size distribution is shown in
Table 1.

Chemical grouting has been successfully andintensively used in engineering practice, including
seepage prevention for dam safety, ground
improvement in mining, renovation of ruptured shaftsin mines. Under complex geological conditions, themechanical properties of chemical grouted sands are
the main factors in the consideration of choosing
grouts (Sui, et al., 2008; Ge, 2006). Moreover, curingconditions, including curing temperature and curing
time directly affect the performance of chemical
grouts (Xia, et al., 2001). The influence of curingconditions on the chemical grouted sands has attracted
interests of many researchers. The curing conditions
they considered are usually limited to single condition,such as curing time and mixture ratio of slurry (Dashet al., 2003). Therefore, the influence of multi-factors
on the properties of grouted sand is worth further
studying. Grout concentration, curing time,
temperature are selected as the main factors. As well,
the microstructure of grouted sand has been analyzed
in this paper.
2. Materials and methods

Table 1 Particle size distribution of a coarse sandParticle size
(mm)
2-0.5

0.5-0.25

0.25-0.075

55%

25%

20%

d10
(mm)

Cu

Cc

0.16

4.7

1.1

Chemical grout slurry used in this study weremade of urea-formaldehyde resin (Component A) andacidic curing agent (Component B). Component A
was composed by urea-formaldehyde resin and 4%
additive, the concentration of acidic curing agent is
2%, A: B = 10: 3 by volume.
2.2 Sample preparation(1) Dry coarse sands were prepared according toTable 1 and stirred well in a bowl, then chemical grout

2.1 Testing materials
Chemical grouted sands are composed by sands

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10th Asian Regional Conference of IAEG (2015)

slurry were prepared according to planed proportion.
The concentrations of grouts are 10%, 30%, 50%,
70%, respectively.
(2) Sample molds were made using PVC pipes
with different diameters and heights, which employed
to do unconfined compressive strength test, direct
shearing test and conventional permeability test.
(3) 10% water were added into the well mixed
sand, then chemical grout slurry with different
concentrations were added into the sand respectively
and stirred well with coarse sand. The mixed coarse
sands were filled to different sample molds.
(4) Prepared samples were put into the thermotank,and cured according to the test plane.

2.3 Orthogonal test design
Orthogonal test is a useful technique to reduce thenumber of test cases, which can be used to optimize
experiment of multi-factor multi-index (Wu, 1997),
and the optimum test scheme can be formulated basedon tests results. Three factors, including grout
concentration, curing temperature and curing period,
were considered and each of them has 4 values.
The concentrations of chemical slurry are 10%,30%, 50%, 70%, respectively. Curing period used inthis experiment are 7, 14, 30, and 60 days. The curing
temperature are 20 , 30 , 40 and 50 . 16 tests
were designed according to L16 orthogonal tables.
Table 2 shows the results.

Table 2 Results of orthogonal test
Tests results

factors

1

A1B1C2

10

B
Curingperiod(day)
7

2

A1B2C1

10

14

3

A1B3C3

10

4

A1B4C4

5

Trial No.

3.

SymbolA
Concentration(%)

C
Curingtemperature(℃)
30

qu (kPa)K(10-5cm/s)

Shear strength
C(kPa)

ф（°）

20.00

1.07

28.76

33.4

20

24.67

2.17

44.26

19.3

30

40

50.00

9.57

50.12

28.0

10

60

50

63.9

3.83

54.80

33.8

A2B1C130

7

20422.65

0.80

87.75

31.8

6

A2B2C230

1430

279.44

1.11

56.65

33.8

7

A2B3C4303050440.66

8.30

26.66

37.2

8

A2B4C330

60

40

244.94

2.11

94.05

20.3

9

A3B1C350

740

676.590.40

133.2933.4

10

A3B2C450

1450600.240.80

151.07

24.2

11

A3B3C250

30

30

739.94

6.58

89.61

27.0

12

A3B4C15060

20466.181.32

144.64

10.8

13

A4B1C470

7

50

933.560.30

130.0038.7

14

A4B2C370

1440

1148.390.64

148.1038.0

15

A4B3C17030

201199.94.81

265.8420.3

16

A4B4C270

60

30

635.941.18

179.94

26.6

Experimental results and analysis

shear tests. In order to reduce the error of test, parallel
tests were conducted in those 16 test groups shown in
Table 2. Unconfined compressive strength test
includes 3 samples in each group, permeability test
includes 2 samples, shear strength test contains 4
samples, and the final value of parameter can becomputed by averaging all samples in each group.

Unconfined compressive strength (ASTM D2166),
hydraulic conductivity (ASTM D5084-03), shear
strength (ASTM D3080) of grouted sand samples
were respectively obtained from uniaxial compression
strength test, falling head permeability test, direct2

10th Asian Regional Conference of IAEG (2015)

temperature is 50 .
3.1 The factors analysis of unconfined compressive
strength
The results show that there are differences among
the unconfined compressive strength of each group.
The minimum value is 20 kPa, while the maximum is1199.9 kPa. This shows that different curingconditions have obvious effects on the unconfinedcompressive strength of the chemically grouted sands.
The result of unconfined compressive strength wasshown in Table 4.
Where, Ki（i= 1, 2, 3, 4）is the average value ofcorresponding columns at i value for each factor, R isthe difference between the minimum and maximum
value of Ki . In this process the data are describedusing one of two possible descriptions: ‘the larger the
better’, ‘the smaller the better’. In this study, the valueof K i and R are related to the form ‘the larger the
better’ following its characteristic.
Table 3 shows the most important factor for
unconfined compressive strength is the slurry
concentration, followed by curing period, finally is thecuring temperature. The best ratio is A4B3C3, thatslurry concentration is 70%, curing period is 30 days
and the curing temperature is 40 .

Table 4 Orthogonal analysis of shear strength factors

A (%)

B (d)

C (℃)

C (℃)

K1

44.45594.950135.623

K2

66.278100.02088.740K3

129.653

108.027106.360

180.970
136.515118.358
23.40890.63246.883

A4

B4

C1

—
—

K4
R
Recommended
ratio

A4B4C1

3.3 The factors analysis of hydraulic conductivity
Table 5 shows hydraulic conductivity ofchemically grouted sands range from 0.3×10-5 ~9.57×10-5 cm/s. The lower of hydraulic conductivity,
the higher seepage resistance. Orthogonal analysis
results are shown in Table 5.
Table 5 Orthogonal analysis of hydraulic conductivity
factors
Factorsqu（kPa）

A(%)

B(d)

C(℃)

K1

4.160

0.642

2.275

—

39.64

513.2

418.83

K2

3.080

1.180

2.485

K2

346.923513.185528.350

K3

2.275

7.315

3.180

K3

620.737607.625

529.980K4

979.447352.740

509.590

1.732
2.428

2.110
6.673

3.308
1.033

R
Recommended
ratio

939.805254.885111.150

K4
R
Recommended
ratio

A4

B1

C1

A4

B3

C3

—
—

—

A>B>C

K
(10 cm/s)
-5

—

K1

—

A>C>B

—

—
—

c (kPa)—Table 3 Orthogonal analysis of unconfinedcompressive strength factors
FactorsA (%)

Factors
B (d)

B>A>C

A4B1C1A4B3C3The most important factor for permeability iscuring period, the followed is slurry concentration,
curing period is the final one. The best ratio is A4B1C2,
which slurry concentration is 70%, curing period is 7
days, curing temperature is 20 .

3.2 The factors analysis of shear strength
As can be seen from Table 2, cohesion ranges
from 26.66 kPa to 265.84 kPa, internal friction angle
ranges from 10.8° to 38.7°. Compared with Test
No.1-8, cohesion of Tests No.9-16 are relatively large.
Orthogonal analysis results of shear strength factors
are shown in Table 4.
The results indicate that the main factors oncohesion are slurry concentration, curing temperatureand curing period. The best ratio is A4B4C2, that slurry
concentration is 70%, curing period is 60 days, curing
temperature is 20 .
Curing temperature has remarkable effect internal
friction angle, and the followed is curing period andslurry concentration. The best ratio is A4B1C4, slurry
concentration is 70%, curing period is 7 days, curing

4.

The micro-structure change of chemicallygrouted sands in different curing condition

4.1 Micropores characteristics before unconfinedcompressive strength test
All the sand samples to be tested after 7 days, andgrouting concentration are 10%, 30%, 50%, 70%.
Figure 1 shows the micropores size distribution ofchemical grouted sands in different grouting
concentration before unconfined compressive strength
test.

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10th Asian Regional Conference of IAEG (2015)

Figure 1(a) shows cumulative pore volume
decrease with the increase of grouting concentration.
This means the pore volume of grouted sand decreases.
When the value of pore diameter is 4 μm, incremental
pore volume of grouted sand is the same in different
grouting concentration. Cumulative pore volume
increases with the increase of grouting concentration
when the value of pore diameter is larger than 4 μm.
However, incremental pore volume of grouted sanddecrease with the increase of grouting concentration
when the value of pore diameter is smaller than 4 μm.
Therefore, 4 μm can be called the critical pore
diameter.

curve pattern when the grout concentration is 70% andthe pore diameter ranges from 500 to 1000 μm. The
high concentration may contribute to this unusual
pattern.

(a) Cumulative pore volume(a) Cumulative pore volume(b) Incremental pore volume
Fig. 2 Proe size distribution for chemical grouted
sand after test

4.2 Micropores characteristics after unconfinedcompressive strength
In comparison with Figure 1, it can be noted thatthe micro-structure of chemically grouted sands
change a little before and after unconfinedcompressive strength test. Figure 2(a) shows the
cumulative pore volume decreases with increasing
grout concentration. Figure 2(b) shows that when thevalue of pore diameter is 6 μm, incremental porevolume reaches the peak value no matter what
grouting concentration is. And before and after test,
the relationship between incremental pore volume and(b) Incremental pore volume
Fig. 1 Pore size distribution for chemically grouted
sands before test
Figure 1(b) shows the relationship between
incremental pore volume and pore diameter. When thepore diameter is 100μm, the value of incremental porevolume reaches the peak value no matter what thegrout concentration is. However, there is an unusual410th Asian Regional Conference of IAEG (2015)

pore before test is similar, only the pore volume
relatively decreased.

Cumulative Pore Volume
Mercury Extrusion

10000
Pressure / psia

4.3 The pore connectivity of chemically grouted
sands
Figure 3 shows the relationship between pressure
and pore volume for grouted sand with different slurry
concentrations. The curves of mercury intrusion andextrusion volume changes obviously, which means thepore connectivity of grouted sand varies a lot. All
curves plotted in Figure 3 shows that there are
overlaps between the mercury intrusion pore volume
curves and mercury extrusion pore volume curves,which indicate that there are a certain number ofclosed pores in the grouted sand. And there are also
some differences between mercury intrusion volume
and extrusion volume, which reflects the poreconnectivity and hydraulic conductivity of grouted
sands. A bigger volume differences mean a better poreconnectivity and a higher hydraulic conductivity ofgrouted sands. Compare with grouted sands with 50%
and 70% slurry concentrations, grouted sands with
10% and 30% slurry concentrations have a better poreconnectivity and higher hydraulic conductivity. The
volume difference of grouted sand with 70% slurry
concentrations has the minimum value, which implies
the worse pore connectivity and hydraulicconductivity, and more closed pores.

1000

100
0.10 0.15 0.20 0.25 0.30 0.35 0.40
Cumulative Pore Volume / ml/g(a) Concentration 10%

Cumulative Pore Volume
Mercury Extrusion

Pressure / psia

10000

1000

100
0.10

0.15

0.20

0.25

0.30

0.35

Cumulative Pore Volume / ml/g(b) Concentration 30%
Cumulative Pore Volume
Mercury Extrusion

5.

Conclusions(1) The orthogonal tests show that, the mostimportant factor for unconfined compressive strength
is the slurry concentration. The main factors oncohesion are slurry concentration, curing temperatureand curing period. Curing temperature has remarkableeffect on the internal friction angle. The mostimportantfactorinfluencing
thehydraulicconductivity is curing period.
(2) The results of mercury intrusion porosimetry
show that the cumulative intrusion pore volumes
decrease with increasing slurry concentration mixed ingrouted sand. This implies that the porosity of grouted
sand increases with decreasing slurry concentration.
(3) The morphology of the mercury intrusion andextrusion volume curve changes obviously, whichmeans the pore connectivity of grouted sands varytremendously. Porosity and pore connectivity would
directly impact the hydraulic conductivity of grouted
sand, it implies that lower porosity and worse poreconnectivity will cause low hydraulic conductivity ofgrouted sands.

Pressure / psia

10000

1000

100
0.10

0.15

0.20

0.25

0.30

Cumulative Pore Volume / ml/g(c) Concentration 50%
Cumulative Pore Volume
Mercury Extrusion
Pressure / psia

10000

1000

100
0.10

0.15

0.20

0.25

0.30

Cumulative Pore Volume / ml/g

Acknowledgements(d) Concentration 70%
Fig. 3 The mercury intrusion and extrusion
volume curves of grouted sand before test

The authors would like to acknowledge thefinancial support of the Natural Science Foundation ofChina under Grant No. 41172291.

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10th Asian Regional Conference of IAEG (2015)

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Ge, J. (2006): Develop and Prospect of Chemical
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