Use of resistivity tomography in underground excavation and

tunneling

Hideo KOMINE

Central Research Institute of Electric Power Industry, Japan

Panelist Presentation by Komine,11th Asian Regional Conference on ISSMGE, Seoul in 1999

Chemical grouting

Chemical grouting is widely used as an auxiliary method when underground structures such as shield tunnels are constructed in large cities.

The main purposes are to reinforce the ground and to reduce the ground permeability.

Use of chemical grouting

▽

Shield tunneling machine

Ground reinforcement

Improved region

Pile foundation

for stabilization of cutting face

Weak point

It is difficult to evaluate the improved region. In chemical grouting, a method to evaluate the region improved by the grouting has not yet been established.

This weak point has been a major obstacle to the enhancement of reliability of chemical grouting.

Electrical resistivity

The electrical resistivity of chemical grout is much lower than that of the ground and ground water.

The resistivity tomography can measure the resistivity distributions of ground before and after chemical grouting in the field.

Advantage of resistivity

Resistivity

Grout << Ground, Ground water

(0.6) (50-300) (20-80)

(): Rough value of resistivity, Unit : m

The resistivity of grout material is one tenth and/or one hundredth of ground and ground water.

It is easy to watch the grouted region by electrical eyes

Potential electrodesC1

C2

Ground surface

:Electrical resistivity of ground

electric line of force

P1

P2

Current electrodes

The potential difference betweenP1 and P2 is measured when theprescribed electric current flowsfrom C1 to C2.

Resistivity tomographyApparent resistivities corresponding the electrodes arrangement.

Start

Initialization of each resistivity block

Calculation of apparent resistivity by FEM

Calculation of residual between theoretical values and measured values of apparent resistivity

Does it satisfy the conversion conditions?

Output of final model ground

Finish

Correction of resistivity values for each block by means of non-linear least-squares method

No

Yes

FEM analysis

Resistivity of grouted sand

Piston

Top cap

Drainage canal

Triaxial cell

Pedestal

To pore water pressure gauge

Insu

lato

r

Co

ppe

r e

lect

rod

e

Specimen Diameter : 50mm Height : 100mm

To electric resistancemeasuring apparatus

Electric wire

Specimen is covered with a rubber membrane

Test apparatus with copper electrodes

There is a close connection between Grout/Void ratio and resistivity.Grout/Void ratio is the volume ratio of grout occupying the void space of ground. It is a representative characteristic of the quality of grouted soils.

40

30

20

10

0120100806040200

Ele

ctric

al r

esis

tivity

sg

:

・m

Grout/Void ratio : %

sg = 90 - 100 ・m, when = 0%

○ : Toyoura sand e = 0.65 - 0.76 w = 10.7 - 22.7 ・m

□ : Mikawa silicate sand No. 3 injected by Grout B e = 0.64- 0.70 w = 34.4 - 50.9 ・m

△ : Mikawa silicate sand No. 7 injected by Grout B e = 0.69 - 0.75 w = 10.2 - 22.4 ・m

sg = 40 - 60 ・m,

when = 0

Resistivity model

We proposed the resistivity model of ground before and after chemical grouting on the basis of laboratory test results.

We investigated the validity of the evaluation proposed.

Rw

As Aw

Ls= Lw =Lg

Rg

Ag

Parallel model for ground after grouting

Sand particle

Rs

Pore water

Grout gel

RwRs

I

VRg

Series model for ground after grouting

As Aw

Ls = Lw

Ag

Grout gel RgLg

Sand particle

Rs Rw

Pore water

Parallel model for ground after grouting

Series model for ground after grouting

Combination model

I

V

I

RwRs Rg

V

RwRs

I

VRwRs

As Aw

Ls Lw

Sand particle

Pore water

Parallel model for ground before grouting

In Komine (1992, 1997)

Validity of resistivity modelE

lect

rical

re

sist

ivity

sg

:

・m

Grout/Void ratio : %

Mikawa silicate sand No. 5

40

30

20

10

0120100806040200

: Result evaluated by the proposed method

: Test results

40

30

20

10

0120100806040200

: Result evaluated by the proposed method

: Test results of Grout A : Test results of Grout B : Test results of Grout C

Ele

ctri

cal r

esi

stiv

ity

sg :

・

m

Grout/Void ratio : %

Toyoura sand

The evaluation of Grout/Void ratio, which is the representative characteristics of the quality of grouted ground, by electrical resistivity was proposed on the basis of the electrical resistivity models of ground before and after chemical grouting.

The validity of the evaluation was demonstrated by the comparison of the evaluation results with the laboratory test results.

1.0

0.8

0.6

0.4

0.2

0.0

注入

後の

比抵

抗

sg／

注入

前の

比抵

抗

sw

100806040200

薬液充填率 α (%)

Res

isti

vit

y r

ati

o b

efo

re a

nd

aft

er

gro

uti

ng

Grout/Void ratio (%)

effectiveness of grouting

A

B

C

Grout/Void ratio established by

ground reinforcement and

reduction of ground permeability

Minimum Grout/Void

ratio having the effect

of chemical grouting

ineffectiveness of grouting

Resistivity ratio before and after grouting - Grout/Void ratio curve

In Komine & Nishi (10ARC, 1995)

We proposed the evaluation of chemical grouted region using the resistivity model proposed and resistivity tomography.

Evaluation using resistivity model and resistivity tomography

Apparatus in the laboratory

Planeview

Vertical section

300 470

580

Model ground

Pole with built-in copper electrodes

Model ground

Injection pipe

Injection pipe

270

1

2

3

4

5

6

7

8

9

1

2

3

4

5

6

7

8

9

A

B

C

D

To drainage

: Copper electrode

Unit of dimensions : mm

50

Pressure gauge Injecting chemical grout

To electric resistance measu

To drainage

Example 1 of evaluation

1

2

3

4

5

6

7

8

9

1

2

3

4

5

6

7

8

9

0.854 0.500 0.429 0.232 0.382 1.288 0.157 0.605

0.026 0.016 0.013 0.016 0.022 0.030 0.016 0.029

0.009 0.008 0.010 0.013 0.011 0.019 0.031 0.010

0.005 0.012 0.011 0.016 0.013 0.016 0.012 0.030

0.014 0.033 0.050 0.046 0.032 0.026 0.022 0.027

0.027 0.052 0.058 0.023 0.028 0.039 0.035 0.120

3.495 0.609 0.084 0.102 0.370 0.258 0.205 0.178

1.935 0.716 0.489 0.526 1.073 1.167 0.736 0.250

Improved regionevaluated by resistivity

Solidified regionconfirmed by eye

Value shown in blocks : Resistivity ratio before and after chemical grouting

1,2,...9 : Copper electrodes

Example 2 of evaluation

1

2

3

4

5

6

7

8

9

1

2

3

4

5

6

7

8

9

1.236 1.906 0.905 2.030 2.159 1.424 2.115 0.587

1.380 1.444 1.239 1.529 1.807 1.519 1.691 1.351

0.790 1.055 2.015 2.039 2.433 1.765 1.694 1.648

0.283 0.570 0.775 0.983 1.285 0.877 0.711 0.272

0.471 0.217 0.465 0.976 1.118 0.587 0.234 0.231

0.010 0.012 0.019 0.027 0.026 0.017 0.011 0.006

0.005 0.012 0.018 0.018 0.017 0.012 0.050 0.003

0.015 0.018 0.036 0.038 0.035 0.014 0.011 0.005

Improved regionevaluated by resistivity

Solidified regionconfirmed by eye

Value shown in blocks : Resistivity ratio before and after chemical grouting

1,2,...9 : Copper electrodes

Resistivity contrast of grout and ground water

C

1

2

3

4

5

6

7

8

9

A

1

2

3

4

5

6

7

8

9

2.000 0.998 0.820 1.535 1.604 0.787 2.679 0.753

0.655 1.446 1.812 0.805 0.735 0.893 1.151 1.250

0.945 0.853 0.566 0.554 0.426 0.416 0.746 0.432

0.045 0.027 0.016 0.029 0.028 0.026 0.020 0.050

0.073 0.013 0.028 0.067 0.086 0.035 0.016 0.039

0.040 0.049 0.010 0.016 0.017 0.011 0.021 0.034

0.098 0.141 0.082 0.052 0.064 0.076 0.136 0.122

0.200 0.212 0.121 0.067 0.043 0.060 0.055 0.064

Contrast of resistivity = High Resistivity ratio Grout/Ground water = 0.020

C

1

2

3

4

5

6

7

8

9

A

1

2

3

4

5

6

7

8

9

0.8941.142 1.354 1.918 1.450 0.619 0.428

0.476

1.443 1.208 4.426 4.354 2.101 0.775 0.338 0.521

0.871 2.980 1.728 1.713 1.795 2.604 0.670 0.442

1.463 2.355 4.283 1.293 1.108 0.755 0.628 0.383

1.154 2.101 2.727 1.972 0.687 0.691 1.222 0.216

0.973 1.979 1.741 1.909 1.257 0.974 0.351 0.904

0.497 2.243 3.026 1.563 0.239 0.390 0.694 0.547

0.822 1.441 1.358 0.548 0.219 0.353 0.655 0.825

Contrast of resistivity = Low Resistivity ratio Grout/Ground water = 0.474

Applicability2.0

1.5

1.0

0.5

1.00.80.60.40.2

Reduction of resistivity is remarkable.

Resistivity ratio, Grout/Ground water≦ 1/10. Improved region can be evaluated by resistivity changes.

0.00.0

Resistivity ratio, Grout/Ground water＞1/10. It is difficult to evaluate improved region by resistivity changes.

: Test results,R

esis

tivi

ty c

han

ges

of

imp

rove

d r

egio

n

Resistivity ratio, Grout/Pore water

Typical range of contrast between grout and ground water

Contrast of resistivity between grout and ground water

In Komine & Nishi (IS-Tokyo’96, 1996)

Resistivity of commonly used grouts

Grout material Resistivity m

Hydrated sodium-silicate grout witha concentration of 35%

, hardener material : Glyoxal(non-particulate grout)

0.62

LW grout, cement + sodium silicate

(particulate grout)

1.30

Silica Sol grout 0.4

Water Resistivity : m

Ground water 20-80Surface water 100-300

Sea water 0.3

The resistivity ratio between grout and ground water is generally less than 1/10. Therefore, the evaluation method of improved region by resistivity tomography is available in most cases except near the sea.

Verification by field test

1000 literTotal

575 literWater

25 literGlycerin-triacetate

400 literSodium silicate

Field test site.

1.5m1.5m

Injection pipe

Plane view

boring hole

grouted region

Ground surface

G.L.-7.7m

G.L.-9.7m

3.0m

Shaft

G.L.-6.5m

G.L.-8.1m

G.L.-8.7m

G.L.-9.3m

G.L.-10.3m

4.2m

4.6m

1

2

3

4

5

6

Vertical section

: boring hole

grouted region Injection

pipe

: grouted region

Shaft

Ground condition.

20

15

10

5

0

地盤

深度

(m

)

50403020100

N値

G.L.-7.7 m

G.L.-9.7 m

▽G.L.-1.35 m

Groundwater level

grouted region

De

pth

(m)

N-value

Loam

Fine sand

Tuffaceous clay

Silty sand

Silty sand

Silty fine sand

Grain size distributions.

Proportion of grout.

(Gelling time = 30 - 40 minutes)

100

80

60

40

20

0

Pe

rce

nta

ge

pa

ssin

g

0.001 0.01 0.1 1 10

Grain size : mm

: Test site : Toyoura sand : Mikawa silicate

sand No. 3 : Mikawa silicate

sand No. 7

In Komine (11ARC, 1999)

0.6

0.5

0.4

0.3

0.2

0.1

0.0

Res

istiv

ity r

atio

, sg

/sw

100806040200

Grout/Void, (%)

:Void ratio =0.39

:Void ratio =1.04

sand =1000 ･m

water =15.0 ･m

grout =0.4 ･m

(sg/sw)cr = 0.1

Evaluation by resistivity model

In this site, the region of resistivity ratio, which is less than 0.1, can evaluate the improved region.

How to measure in the field

.

▽ ▽

1

Potentialelectrodes

Currentelectrodes

G.L.-6.5m

G.L.-10.5m

G.L.-12.0m

Dipole length : 500mmShift interval : 250mm

Dipole length: 500mm

Shift interval: 250mm

G.L.-0.0m

P1 P2 C1 C2

1

456789

1011121314151617

23

1

456789

1011121314151617

23

8

1 5

Vinyl chloride pipeDiameter, Inner : 65 mm, Outer : 76 mm

G.L.-12.0m

G.L.-11.0m

G.L.-6.0m

G.L.-9.7m

G.L.-7.7m

Region for sampling(Grouted region)

G.L.-6.5m

G.L.-10.5m

Region ofresistivitymeasurement(4.0m)

Filling upby sand

86 mm

76 mm

Ground surface

Borehole.

Pipe was wrappedby filter forpreventing theinflow of sand.

Measurement of resistivity.

Region ofresistivitymeasurement(4.0m)

Apparatus formeasuring resistivity

Connectionbox

3000 holeswere made.

Results

(a) 1 -2 section

1 2

20 19 18 18 18 18 19 20 25 29

16 15

17

15

14

16

13

16

13

17

14

17

14

17

15

19

15

24

16 16

19 17 15 14 13 13 15 18 23 25

17 16 14 12 10 10 11 13 19 25

11 11 10 9 9 9 9 10 13 20

6 5 5 5 6 6 6 6 6 7

2 2 3 3 3 3 3 3 3 3

3 3 3 4 4 3 3 3 3 6

3 3 3 4 4 4 3 4 4 4

4 4 4 3 3 3 4 4 4 4

4 4 4 3 3 3 3 3 4 5

4 4 3 3 3 3 3 3 4 4

7 6 6 6 6 6 7 8 9 13

11 14 15 16 16 16 16 17 18 18

16 19 22 23 24 24 24 24 23 24

G.L.-6.5m

G.L.-7.0m

G.L.-7.5m

G.L.-8.0m

G.L.-8.5m

G.L.-9.0m

G.L.-9.5m

G.L.-10.0m

G.L.-10.5m

1.53m

(c) 4-5 section

29 25 18 16 15 14 17 3321 20

22 20 17 15 12 10 11 1920 19

12 14 12 10 10 10 13 2714 13

3 5 4 3 4 6 15 475 4

3 4 2 1 2 3 10 513 2

3 2 2 2 2 4 8 172 2

1 1 2 2 3 4 6 102 2

2 2 2 3 4 6 8 72 2

2 2 2 2 2 3 5 102 2

2 1 2 3 3 4 5 71 2

1 1 2 2 4 6 7 71 1

3 2 1 1 1 2 5 61 1

8 7 4 3 4 6 10 205 4

19 19 15 11 10 11 14 1817 14

38 34 26 21 18 17 19 2732 29

61 48 31 26 23 22 28 4442 37

4 5

1.21m

(d) 5-6 section

67 53 56 69 68 62 73 103 314 791

22 27 67 85 68 72 86129 150 122

17 20 38 80 67 77 16479 108 98

51 55 62 109 85 69 9691 96 97

175 44 24 115 138 124 6432 49 84

59 84 40 21 12 14 4633 34 31

24 32 9 7 6 9 379 14 13

11 6 10 11 7 13 2825 33 29

3 7 18 16 7 5 5327 38 29

4 5 8 30 13 13 1725 28 32

550 140 55 111 76 26 957 78 104

113

2 15 24 125 58 10 551 63 95

12 1 4 8 6 5 54 6 7

21 18 21 43 5 4 971 36 16

92 237 451 344 150403 49 14 11

400 222 241 33 25 20 2493 47 42

5 6

1.17m

(b) 2-3 section

429 615 778 668

228 350 433 444

420

368

90 108 159 250 333

85 63 86 158 319

78 79 73 90 159

231 157 108 89 100

92 150 133 120 116

90 73 72 76 97

50 54 67 79 96

44 83 142 173 143

52 103 174 190 138

166 175 168 148 110

337 341 269 176 107

435 610 477 261 94

1314 889 555 256 123

452 601 328 189 98

292 164 137 119 122

246 157 109 99 107

326 237 143 91 97

508 557 402 180 64

279 434 444 275 112

132 160 198 204 139

120 129 134 166 209

121 149 168 182 196

112 136 158 172 129

95 70 66 75 134

84 49 37 45 60

75 50 43 48 67

74 59 49 46 31

74 52 40 33 38

66 43 30 22 15

60 40 29 22 22

2 3

1.58m

No improved region evaluated by resistivity

1 2 3

4 65

: Measurement section

Grouted region (G.L.-7.7m - G.L.-9.7m)

: Improved region evaluated by resistivity

: Solidified region confirmed by boring investigation

No solidified region confirmed by boring investigation of No. 3 hole

Another site (Takenaka Corp.)

100

80

60

40

20Per

cent

age

pass

ing

0.01 0.1 1 10 100

Grain size : mm

This site is gravel ground. Average diameter is 40-50mm

Area of chemical grouting

0.5m

5.5m

G.L.-5.0m

G.L.-11.0m

Region of resistivity measurement (6.0m)

G.L.-6.0～8.0m

Electrodes

Gravelly ground

Site condition

Results

2.36 2.79 3.85 4.65 4.85 5.46 7.71 13.14 16.06 11.46 8.02 6.97 7.26 6.97 5.49 4.293.45 3.99 5.24 6.27 6.56 7.12 8.87 11.87 13.06 10.59 8.56 7.94 8.20 7.74 6.17 4.685.99 6.61 8.01 9.29 9.69 9.69 9.71 9.39 8.62 7.67 7.16 7.15 7.36 6.94 5.82 4.439.13 9.75 11.09 12.34 12.39 10.92 8.69 6.38 4.84 3.99 3.76 3.87 4.15 4.23 3.88 3.1211.61 12.01 12.86 13.34 12.57 9.88 6.74 4.13 2.69 1.99 1.78 1.84 2.04 2.23 2.20 1.8811.07 11.20 11.55 11.50 10.50 7.81 4.90 2.65 1.52 1.01 0.85 0.86 0.98 1.11 1.16 1.057.23 7.42 7.81 7.98 7.47 5.70 3.58 1.85 0.99 0.60 0.48 0.47 0.52 0.60 0.66 0.633.68 3.84 4.17 4.51 4.55 3.82 2.62 1.42 0.76 0.44 0.33 0.30 0.33 0.38 0.42 0.421.68 1.81 2.09 2.44 2.69 2.56 1.99 1.22 0.70 0.41 0.29 0.25 0.26 0.29 0.33 0.340.86 0.93 1.09 1.35 1.61 1.72 1.52 1.07 0.67 0.41 0.28 0.23 0.22 0.24 0.27 0.280.51 0.57 0.68 0.88 1.11 1.28 1.22 0.94 0.63 0.40 0.28 0.22 0.20 0.21 0.24 0.250.38 0.41 0.49 0.64 0.83 0.99 0.98 0.79 0.56 0.37 0.26 0.20 0.18 0.19 0.20 0.210.31 0.34 0.41 0.53 0.68 0.80 0.80 0.65 0.47 0.32 0.23 0.18 0.16 0.17 0.18 0.190.28 0.31 0.36 0.46 0.57 0.65 0.64 0.52 0.39 0.27 0.20 0.16 0.15 0.15 0.16 0.160.26 0.28 0.33 0.41 0.49 0.53 0.51 0.42 0.32 0.23 0.18 0.14 0.13 0.13 0.14 0.140.25 0.27 0.31 0.37 0.42 0.44 0.41 0.35 0.27 0.20 0.15 0.13 0.12 0.12 0.12 0.120.26 0.28 0.31 0.34 0.37 0.37 0.35 0.29 0.23 0.18 0.14 0.12 0.11 0.10 0.10 0.090.29 0.30 0.31 0.32 0.32 0.31 0.29 0.25 0.20 0.16 0.13 0.11 0.09 0.08 0.08 0.070.34 0.33 0.32 0.31 0.29 0.27 0.25 0.22 0.18 0.14 0.12 0.09 0.08 0.07 0.07 0.060.38 0.37 0.34 0.30 0.27 0.24 0.21 0.19 0.16 0.13 0.10 0.08 0.07 0.06 0.06 0.050.44 0.41 0.36 0.30 0.25 0.21 0.18 0.16 0.13 0.11 0.09 0.07 0.06 0.06 0.05 0.050.49 0.44 0.36 0.28 0.22 0.18 0.15 0.13 0.11 0.09 0.07 0.06 0.05 0.05 0.05 0.050.50 0.44 0.35 0.26 0.19 0.15 0.12 0.11 0.09 0.07 0.06 0.05 0.05 0.05 0.05 0.050.46 0.39 0.30 0.21 0.16 0.12 0.10 0.08 0.07 0.06 0.05 0.05 0.04 0.04 0.04 0.050.37 0.32 0.24 0.17 0.12 0.09 0.08 0.07 0.06 0.05 0.05 0.04 0.04 0.04 0.04 0.040.29 0.25 0.18 0.12 0.09 0.07 0.06 0.05 0.05 0.04 0.04 0.04 0.04 0.04 0.04 0.040.22 0.19 0.14 0.09 0.07 0.05 0.05 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.040.17 0.15 0.11 0.07 0.05 0.04 0.04 0.03 0.03 0.03 0.03 0.03 0.04 0.04 0.04 0.050.14 0.12 0.09 0.06 0.05 0.04 0.03 0.03 0.03 0.03 0.03 0.03 0.04 0.04 0.05 0.050.12 0.10 0.08 0.05 0.04 0.03 0.03 0.03 0.03 0.03 0.03 0.03 0.04 0.05 0.05 0.060.10 0.09 0.07 0.05 0.04 0.03 0.03 0.03 0.03 0.03 0.03 0.04 0.04 0.05 0.06 0.060.09 0.08 0.06 0.05 0.04 0.03 0.03 0.03 0.03 0.03 0.04 0.04 0.05 0.05 0.06 0.060.08 0.07 0.06 0.05 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.05 0.05 0.06 0.06 0.060.07 0.07 0.06 0.05 0.04 0.04 0.04 0.05 0.05 0.05 0.05 0.06 0.06 0.06 0.07 0.070.07 0.07 0.06 0.05 0.05 0.05 0.05 0.05 0.06 0.06 0.07 0.07 0.07 0.08 0.08 0.080.07 0.07 0.06 0.05 0.05 0.05 0.06 0.06 0.07 0.08 0.08 0.09 0.09 0.10 0.10 0.09

0.08 0.07 0.06 0.06 0.06 0.06 0.07 0.08 0.09 0.10 0.11 0.12 0.12 0.12 0.120.07 0.07 0.08 0.08 0.09 0.11 0.12 0.13 0.14 0.15 0.15 0.15

0.10 0.11 0.12 0.13 0.14 0.16 0.17 0.17 0.170.15 0.16 0.17 0.17 0.17 0.17

0.17 0.17 0.17 0.160.15

Distance (m)

Dep

th (

m)

0

-2

-4

-6

-8

-10

0 1.0 2.0 3.0 4.0 5.0

By Uchida et al. (1998, Proceedings of the symposium on underground space Vol.4, JSCE)

Conclusions We proposed the evaluation of chemical grouted region using

the resistivity model proposed by author and the resistivity tomography.

We investigated the validity and the applicability of this method by laboratory tests. From the laboratory test results, improved regions evaluated by the proposed method almost agreed with the solidified regions. If the resistivity ratio between grout and ground water is less than 1/10, we can confirm the improved region by this evaluation.

We verified this evaluation by field test. From the field test results, we confirmed the availability of the evaluation method in practical fields.

References (in English) Komine, H. 1992. Estimation of chemical grout void filling by

electrical resistivity. Grouting, Soil Improvement and Geosynthetics Proceedings, ASCE. New Orleans: 372-383.

Komine, H. and Nishi, K. 1995. Evaluation of grouted region by resistivity changes. Proceedings of the 10th Asian Regional Conference on Soil Mechanics and Foundation Engineering, Vol. 1: 413-416.

Komine, H. and Nishi, K. 1996. Applicability limit of resistivity to evaluate improved region. Proceedings of IS-Tokyo ﾕ 96 (Grouting and Deep Mixing), Vol. 1: 159-164.

Komine, H. 1997. Evaluation of chemical grouted soil by electrical resistivity. Ground Improvement, Vol. 1: 101-113.