10th Asian Regional Conference of IAEG (2015)

Experimental Study of Grouting for Mechanical Improvement of Bedrock
S.Utsukia*a

HAZAMA ANDO Corporation, Tokyo, Japan*utsuki.shinji@ad-hzm.co.jp (corresponding author’s E-mail)
Abstract
Grouting is performed to mechanically improve the deformation and strengthcharacteristics of bedrock by filling cracks with cement so that the entire bedrock is
integrated and homogenized. For verifying the improvement, however, only permeability iscurrently considered because it is difficult to track other mechanical properties. For thisreason, today dam foundation design cannot fully account for improvements, even thoughmany construction activities are carried out to improve the mechanical properties of dam
foundations.
Against this background, we compared the results of borehole loading tests andindoor shear tests, before and after grouting. Based on the test results, the mechanicalimprovement of bedrock by grouting was characterized in order to develop a way to
account for the mechanical improvement of bedrock in dam foundation design.
Keywords: Consolidation Grouting, Dam Foundation, Mechanical Improvement, Experimental Study

1.

Introduction

2.

Grouting is performed to mechanically improvethe deformation and strength characteristics ofbedrock by filling cracks with cement so that theentire bedrock is integrated and homogenized. For
example, consolidation grouting for a dam foundation
is carried out to improve mechanical properties and to
reduce seepage flow. For verifying the improvement,
however, only permeability is typically considered
because it is difficult to track other mechanicalproperties. For this reason, today dam foundation
design cannot fully account for improvements, eventhough many construction activities are carried out toimprove the mechanical properties of dam
foundations.
Against this background, we compared the resultsof borehole loading tests before and after grouting insix types of in situ bedrock at 14 dam sites to
examine in detail the improved deformation
characteristics for various bedrock and rock types.
Furthermore, we quantitatively confirmed thestrength improvement by performing indoor shear
tests, before and after grouting, using test specimens
with cracks. Based on the test results, the mechanicalimprovement of bedrock by grouting wascharacterized in order to develop a way to account forthe mechanical improvement of bedrock in dam
foundation design.

In situ bedrock tests and indoor shear tests

2.1 Overview of in situ bedrock tests
In situ tests were carried out at several positions
in a borehole before and after the grouting
construction as shown in Fig. 1, and the changes inphysical deformation parameters were determined bycomparing the test results. Fig. 1 shows the in situ
test positions in the borehole and the test flow. First,
カバーロックCover rock
1～2m
1～2m

載荷中心
Depth 1.5m
区間深度 1.5m

Test point
載荷区間
60cm
60cm

Experiments before grouting

Drilling↓
Observation of boring core↓
Borehole load test↓
Grouting

載荷中心
Depth 2.5m
区間深度 2.5m

Borehole
注入区間
5m5m

Lusion test↓
Grouting↓

Depth 3.5m
載荷中心区間深度 3.5m

Experiments after grouting

Re-boring↓
Borehole load test

Fig.1 Flowchart of in situ experiments.

1

10th Asian Regional Conference of IAEG (2015)a borehole of 66 mm in diameter and 5 m in length
was prepared (cover locking portion: 1-2 m; grouting
portion: 5 m) the borehole was measured and logged,
and borehole load tests were performed at depths of
1.5 m, 2.5 m, and 3.5 m at the center of the 60 cm
loading section. The Lugeon test was first carried out
to observe the water permeability of bedrock in the 5m construction section and then grouting was
performed. Next, the grout in the borehole was
re-bored, and borehole loading tests were carried out
at the same positions as before the grouting; thechanges in physical properties were examinedthrough a comparison with the results before grouting.
These tests were done at the dam construction sites in
14 places and 5 kinds of rock types as shown in Table
1. And, in this study, the rock mass classification atdams in Japan as shown in Table 2 is applied.

Table 1 Rock types of experimental sites.
Rock type
GraniteIgneous rock
Rhyolite

SedimentaryrockAndesite
Sandstone
Tuff breccia

Measuring points
H dam
313 points
Y dam
N dam
K1dam
K2dam
87 points
O1dam
G dam
62 points
S dam
66 points
M dam
136 points

Table 2 Rock mass classification in Japan
Rock massclassfication

B～CH
class
CM class
CL～D
class

2.2 Overview of indoor shear testsa) Shear test method without considering crack
junctions
Grouting was performed using mortar test
specimens to model cracks in bedrock, and thebefore-and-after shear test results were compared toevaluate the improvement of bedrock strength by
grouting. Five bedrock blocks containing joint facesof volcanic rocks were collected, and eight test
specimens per joint face were fabricated by firstmaking a highly liquid silicone mold for the upperand lower joint faces and then pouring mortar into it.
The test specimen is 30 cm wide, 30 cm deep and 20
cm tall (Fig. 2); a joint face is located in the middleof the test specimen. The mortar was composed of a
4:2:1 mix of sand, cement, and water and waswater-cured for two months after grouting.
An injector device was fabricated to performgrouting along the joint face in four out of eightspecimens prepared for each type of joint face. In
evaluating the improvement effect of grouting on theshear strength of bedrock, shear strength wascompared between the test specimens with andwithout grouting. Four levels of vertical stress wereapplied to the five sets of test specimens that model
cracks, with each set composed of a pair of
specimens before and after grouting, and direct shear
tests were performed by applying the shear load witha displacement speed of 1 mm/min.

Deformability
Modulus of Modulus ofdeformation
elasticity(N/mm2)(N/mm2)

Strength
Angle of
Cohesion
2
internal(N/mm )
friction (°)

Elastic wave
velocity(km/s)～2,000～4,000

～2.0

～40

～3.0

2,000～
500
500～04,000～
1,500
1,500～0

2.0～1.045～30

3.0～1.5

1.0～0

38～15

1.5～0

Fig.2 Test specimen for shear tests.

(a) 4 junctions(b) 2 junctionsb) Shear test method considering the junctions ofcracksWe assume the continuity of a joint is limited in
bedrock; the joint may not be completely separated
and may have initial adhesion strength. Therefore we
fabricated test specimens with artificial junctions
having initial adhesion strength. After fabricating test
specimens by pouring mortar into a mold as
described for the in situ bedrock tests, boreholes of
40 mm in diameter were prepared as shown in Fig. 3(c) 1 junction

Fig.3 Test specimens considering the junctionsof cracks2

10th Asian Regional Conference of IAEG (2015)

in eight test specimens per joint type, and junctions
were prepared by filling with mortar. For joint 1, in
addition to the layout in Fig. 3(a), eight test
specimens were fabricated for layout (b) and also forlayout (c).

Modulus of deformation after grouting(N/mm2)

10000

3. Improvement effect on bedrock deformation
characteristics
3.1 Integration of bedrock
The integration of bedrock means the
improvement of mechanical properties such as
deformation characteristics by hardened cement,
which was filled into the cracks of the bedrock. Here,
we discuss the improvement of the modulus ofdeformation of the bedrock for (a) various deformation
modulus classifications and (b) various rock types.
Fig. 4 compares the moduli of deformation at thesame positions before and after grouting for every
deformation modulus classification. The figure shows
an increase in the modulus value at most of thepositions, indicating that the bedrock is integrated bygrouting. Fig. 5 shows in more detail the logarithmic
frequency distribution for every deformation modulus
classification before and after grouting. For ranks CH
and CM-1, the minimum value barely increases
whereas the mean value increases more rapidly thanthat of other ranks. In contrast, for ranks CM-2 andCL-1, the increase in the modulus of deformation is
sharper because the average value increases
moderately and the minimum value increases rapidly;in particular, for rank CL-1, all the measurement
points exhibit values above the minimum value forrank CM. For ranks CL-2 and D, however, there aresome points that show hardly any increase whereas
both the average and average ± standard deviation
increase rapidly.

CH

CM-1

1000
CM-2
CL-1
CL-2
D

Granite
Rhylolite

100

Andesite
Tuff brecia
SandstoneDCL-2 CL-1 CM-2 CM-1

CH

10
10

100
1000
Modulus of deformation before grouting（N/mm2）

10000

Fig. 4 Moduli of deformation at the same positions
before and after grouting
10,0001,000

最大値
Maximum
Average+σ
平均値+σ

Average
平均値

100

平均値-σ
Average-σ
Minimum
最小値□：Before grouting■：After grouting

10

Rock massclassfication

－

CL2

CL1

CM2

CM1

CH
－

Modulus of deformation

0～200

200～350350～500

500～1,000

1,000～2,000

2,000～

NumberMaximum value
Average＋σ
Average
Average－σ
Minimum valueStandard deviation
Coefficient of variation

D

CL

CM

25

25

33

33

29

29

179

179

124

124

200

1,450

340

3,780

500

3,170

1,000

5,440

1,990

5,310

7,800

8,230

90

1,200

360

2,550

540

2,000

1,100

3,330

2,150

4,290

5,150

244

7,350

244

74

330

270

860

440

980

740

1,390

1,430

2,180

2,980

4,000

61

90

190

300

350

480

500

570

970

1,160

1,770

2,160

12
67
0.91

20
470
1.42

210
44
0.16

230
670
0.78

360
45
0.10

500
500
0.51

510
150
0.20

680
920
0.66

1,000
274
0.19

1,020
850
0.39

2,010
920
0.31

2,020
1,280
0.32

Fig. 5 Logarithmic frequency distribution before
and after groutingb) Improvement effects for various rock types
Fig. 6 compares the logarithmic mean values
before and after grouting for each rock type within thesame rank of modulus of deformation. The figure
shows that, in ranks CH to CL, the mean value
increases more rapidly in igneous rock than in
sedimentary rock within every rank. The increased
values of physical parameters might be due to theeasier injection of cement milk, a hypothesis supported
by larger continuous cracks being more frequently
found in igneous rock, especially volcanic rock, thanin sedimentary rock when evaluated by geologicalobservation and measurement and borehole logging at
the dam site.
3.2 Homogenization of bedrock
The homogenization of bedrock leads to reduced
variation in mechanical characteristics. The results forbedrock before and after grouting (Fig. 7) show thatfor every rank of modulus of deformation, theFig. 6 Logarithmic mean values before and after
grouting for each rock type3

10th Asian Regional Conference of IAEG (2015)

variation coefficient tends to increase after grouting for
all ranks and tends to be greater at lower ranks. In
addition, in ranks CH to CL-1, the minimum value ofthe increase in the modulus of deformation increases
more rapidly in lower ranks.
Taking the above into consideration, after grouting
the modulus of deformation increases, in which it
fluctuates toward larger physical parameters within thesame rank. However, since the increase in minimum
value and the upward variation are small at higher
ranks and large at lower ranks, when calculation is
performed using all data, a smaller variation coefficientis obtained after grouting, in other words, homogeneity
is considered to increase.

Ratio before and after grouting

100

10

1

GraniteRhyrolite
Andesite
Tuff brecia
D

Sandstone

CL-2 CL-1 CM-2 CM-1

CH

0.1

4.

Improvement of bedrock strength

10

100

1000

10000

Modulus of deformation before grouting（N/mm2）

Fig. 7 Variation coefficient before and after
grouting

4.1 Evaluation of indoor shear test resultsa) Shear test results without considering crack
junctionsWithout considering junctions, direct shear tests
were carried out using the test specimens before andafter grouting. Fig. 8 shows the relationship between
the vertical stress applied to the joint face and the
maximum shear stress for every type of joint face. The
maximum shear stress after grouting exceeds that
before grouting in all specimens with cracks, clearly
showing that the shear strength is improved. In
addition, the slope of the straight line remains almost
unchanged before and after grouting, and noappreciable change is observed in the internal friction
angle. The improvement effect of grouting on strength
does not exceed the developed adhesive strength of
0.1-0.3 MPa. After the shear test, there wasconsiderable exfoliation at the joint face but thedegradation of grouting materials was rarely observed.
This suggests that the shear destruction of joint faceoccurs not in the grouting material but at the interface
between grouting material and joint face. Further,almost no change was observed in the internal friction
angle, suggesting that the roughness of the shearing
plane is not appreciably changed by grouting.

○：Before grouting●：After grouting

Fig. 8 Test results (4 types of roughness: no intact
bridge)b) Shear test results considering crack junctions
Fig. 9 shows the results of the direct shear test
before and after grouting using test specimens withfour junctions, and Fig. 10 shows the results for a test
specimen with one or two junctions between the cracks
in joint 1. In both figures, the maximum shear stressafter grouting exceeds that before grouting, indicating
the improvement of shear strength. In addition, theslope of the straight line remains almost unchanged bygrouting, indicating that the friction angle does notappreciably change or the shear strength improves asadhesive strength improves. This suggests that, even in
the presence of a junction, improvement isaccomplished by a mechanism like that of a fully
separated surface. In the case of four junctions, the○：Before grouting●：After grouting

Fig. 9 Test results (4 types of roughness: 4 intact
bridges)4

10th Asian Regional Conference of IAEG (2015)

increase in adhesive strength by grouting does notexceed 0.4-0.6 MPa. The improvement effect wasenhanced by the existence of junctions, as shown bycomparison with the results for the case of complete
separation in which the increase in adhesive strength
was 0.1-0.3 MPa.
Dam foundation design considering mechanicalimprovement of bedrock

5.1 Concept of conventional design of dam
foundation
A usual requirement is to perform stability analysis
using Henny's formula to secure the required safety
factor of 4.0 in the design of a dam foundation. In thecalculation, the shear strengths of foundation bedrockas shown in Table 3, which are based on the in situ
shear test results from each dam site, are assumed. In
dam A in Fig. 11, for example, the tests are carried out
using 3 or 4 points for each bedrock type and thedesign value of shear strength is derived based on the
results. In dam foundation design, we generally
perform the stability analysis using Eq. (1) for every
block after dividing the foundation into blocks of 15 m
in length in the dam axis direction. Thus, as in theexample in Fig.12, the calculation will usually showthat we can secure the safety factor of 4.0 in CL classbedrock if the banks are lower than about 40 m inheight where forces such as water pressure are
relatively small while the foundation should be set on
CM class bedrock if the banks are higher than about 40
m. The shape of the bank foundation is finallydesigned to secure the desired safety factor in all
blocks.

Fig. 10 Test results (2 types of intact bridges :No.1)
Table.3 Shear strengths of foundation bedrock
Rank

Dam A

Dam B

CH

C=2.30MPa,φ=48°

C=2.50 MPa,φ=50°

CM

C=1.90MPa,φ=43°

CM1：C=1.90MPa,φ=45°
CM2：C=1.59MPa,φ=45°
CM3：C=1.20MPa,φ=45°

CL

C=1.10 MPa,φ=39°

C=0.79 MPa,φ=35°■■

B:：τ=3.00+σ・tan55°

■

■

●

■

CH：τ=2.30+σ・tan48°

Sheer stress (MPa)●

5.2 Study of dam foundation design considering themechanical improvement of bedrock
Based on the above discussion, in order to set thetwo values of shear strength by dividing the CL classinto two in dam A shown in Fig. 11, we can use theexisting shear strength for the CL class as the value for
the CL2 class and assume an adhesive strength of about
1.50 MPa (the average of the CM and CL classes) for
the CL1 class, as shown in Fig. 13, just as discussed in
Section 3. Then, with respect to the improvement by
grouting, from the discussion in Section 4, we canevaluate the CL1 class assuming adhesive strength ofabout 0.40 MPa without changing the internal friction
angle; as the figure shows, there is a very highlikelihood that the adhesive strength of the CL1 class is
improved to 1.90 MPa by grouting, equivalently to thatof the CM class. By evaluating, for example, theexcavation shape for the dam foundation shown in Fig.
12, assuming that the area of the CL1 class is equivalent
to an area of the CM class due to the improvement by
grouting, we can set the excavation line even higher
than shown in Fig. 14 at bank depth of 40 m and below,
where rock contact of the CM class or above is usually5

CM：τ=1.90+σ・tan43°

◆
◆

●●
●

CL：τ=1.10+σ・tan39°
◆

■：B
▲
▲

●：CH

▲
▲

◆：CM
▲：CL

Normal stress (MPa)Fig.11 Test result of Dam A●●●

Sheer stress (MPa)5.

○：Before grouting●：After grouting◆◆

CM: τ=1.90+σ・tan43°
After grouting
CL1: τ=1.90+σ・tan39°
CL1: τ=1.50+σ・tan39°
CL2: τ=1.10+σ・tan39°

◆
▲
▲
▲
▲

■：B
●：CH
◆：CM
▲：CL

Normal stress (MPa)Fig. 13 Shear strengths of foundation bedrock
due to the improvement by grouting

10th Asian Regional Conference of IAEG (2015)

required. If we can set a higher excavation line for a
CL-CM class excavation site, we could decrease theamount of both bank excavation work and concrete
placement work simultaneously. Moreover, theimprovement would contribute to the aspects of dam
construction—Q (quality), C (cost), D (delivery), S(safety), and E (environment)—by reducing the
excavation volume in the surrounding area such as theupper part of the bank slope, by reducing the
excavation volume at quarry sites through reduced
aggregate production, by securing slope stability
through reduced height of the excavation slope, by
minimizing the alteration of the natural landscape, andby reducing the amount of construction work for slope
protection through the reduced slope area.
6.

Fig.12 Excavation shape for dam foundation

Conclusions

In situ experiments and indoor sheer tests were
executed in order to estimate the improvement of
bedrock by grouting quantitatively. By the results ofthese examinations, authors show the design example
due to improvement by grouting.
In the future, from the knowledge in this paper, we
think that there is a possibility that the improvement
about the mechanical properties by grouting can beconsidered for the dam foundation design.
Fig.14 Design example due to the improvement
by grouting

6