15th International Conference on Ground Penetrating Radar - GPR 2014

Highway Shield Tunnel Inspection using Integrated OPR Equipment Xiongyao Xie*, Hui Qin, Rongjie Yao Department of Geotechnical Engineering, College of Civil Engineering Tongji University Shanghai 200092, China Email: *xiexiongyao@tongji. edu.cn; qinhui@yeah. net; [email protected]

Abstract

-

The Ground Penetrating Radar

(GPR)

is an

11. HIGHWAY SHIELD TUNNEL STRUCTURE

effective method for shield tunnel grouting layer inspection. However, due to the large cross sections of highway shield tunnels,

traditional

manual

inspections

cannot

meet

the

requirement. In accordance with the characteristics of the highway shield tunnel, a vehicle mounted integrated GPR inspection equipment is presented.

Together with manual

inspections, the tunnel can be checked comprehensively. By

The highway shield tunnel usually has an inner diameter of more than ten meters, the structure of which is made of reinforced concrete segments with thicknesses of fifty centimeters or more. Behind the segments distributed the grouting layer of several centimeters. According to the

analyzing the GPR data recorded by equipment and human

tunnel structure gauge and suing function, the inner space of

force respectively, both advantages and limitations of the two

the tunnel is usually separated into several parts, such as

gathering modes are discussed and suggestions are provided.

driveway, fire evacuation route, flue, cable gallery, etc. Fig.

Index Terms-GPR, integrated equipment, highway shield

1 depicts the sketch map of a highway shield tunnel.

tunnel, grouting layer inspection

1. INTRODUCTION

Highway shield tunnels, considered to be one of the most important urban infrastructures, play a critical role in alleviating traffic pressure in big cities. To maintain the stability of the tunnel structure, prevent water leakage, and control ground settlement, grouting behind tunnel segments, proved to be an effective means, is usually applied[1], [2]. For

inspecting

including

the

the thickness

quality and

of

the

grouting

compactness,

layer,

the Ground

Penetrating Radar (GPR) is a promising tool, which is testified in many applications[3]-[6]. However, with the development of tunneling techniques and increasing demand of urban transportation, highway shield

tunnels

common. extremely

of

very

Besides, complex.

large

diameters

become

more

the inner space of the tunnels are These

new

situations

make

grouting layer

the

Fig. l. Sketch map of a highway shield tunnel

traditional human inspection very difficult. On the one hand, manual inspection cannot reach very high positions like the

Subsidiary facilities inside the tunnel are the main

tunnel crown; on the other hand, manual inspection is low

factors that will cause inconveniences for GPR inspection.

efficiency and not safe when the tunnel is operating.

In the crown, a flue is separated from the tunnel by a

Therefore,

high efficient inspection method should be

proposed.

concrete plate. At the haunch, a side wall is set, usually made

of

concrete

or

fiberboard.

At

the

bottom,

the

Tn this paper, characteristics of highway shield tunnels

pavement is casted by reinforced concrete and asphalt.

are presented and an inspection plan is made. Then, an

Under the pavement, there are spaces for cables, pipes and

integrated GPR equipment is proposed, which comprises a

evacuation. These facilities make the tunnel a multi-space

vehicle, a mechanical system, a power system, a controlling

structure.

system and a stepped frequency GPR system. Finally, GPR data of different inspections are processed and analyzed.

According to the layout of the tunnel, GPR survey lines are planned. For the tunnel structure can have one or two layer driveway, survey lines are planned differently for the

978-1-4799-6789-6114/$31.00 ©2014 IEEE

413

15th International Conference on Ground Penetrating Radar - GPR 2014

two cases, as is shown in Fig. 2. Some spaces are not

is shown in Fig. 4. All the devices can be easily transported

accessible for vehicles, so manual survey lines are planed,

by folding them into the truck range.

which are marked triangle. For the survey lines marked round, they are places unreachable for manual survey or not safe for operators and vehicle-mounted survey lines are planned. •

vehicle-mounted GPR S\D'Vey line

Fig. 4. Detection equipment in a folding state When reaching the inspecting spot, the devices can be set up automatically, shown in Fig. 5. The setting up process will last less than fifteen minutes.

Fig. 2. Plan ofGPR survey lines for (a) One layer driveway and (b) Two layer driveway TIT. GPR SYETEM AND DETECTION EQUIPMENT A. CPR

System

We use a stepped frequency GPR system (SF-GPR), including a computer, a Vector Network Analyzer (VNA)

upper arm ---/-.1.

and antennas, shown in Fig. 3. The computer works as a control

unit,

setting

up

data

acquisition

parameters,

recording data and displaying GPR image. The VNA we use pick-up truck

is the Agilent N9923A vector network analyzer, which is used to generate signals. The Vivaldi antennas, which perform well in the frequency band of 400MHz to 3GHz are selected as the signal transmitting and receiving components. Meanwhile, the antennas are sealed in a fiberglass box, which are easy to install on the vehicle.

lower

arm

--.:_�

___

GPR antenna -------'.,:

Fig. 5. Detection equipment in a set up state The pick-up truck is used to carry all the operating personnel and devices. So the inspection can be performed while driving at a speed of 5�10 km/h. The upper

arm

consists of a foundation, a motor, a

reducer, a rotary table, an electric cylinder, a lifting tower and a deflection gear, whose function is to support the antenna and send it to the pre-set location of the tunnel. The

Fig. 3. Stepped frequency GPR system

maximum height of the upper arm is six meters, and the rotation angle of it is -90 to 90 degree within the tunnel

B. Detection Equipment A integrated equipment is designed to mount the GPR system, which comprises a pick-up truck, a controller, a generator, two mechanical arms and a measuring system, as

cross section, which means that the upper arm can reach every comer of the tunnel except for the pavement. Another antenna is installed on the lower arm to inspect the pavement of the tunnel and grouting layer behind the

414

15th International Conference on Ground Penetrating Radar - GPR 2014

bottom segment. According to the design, the gap between

:_-

antenna and ground can be adjusted from Scm to 30cm. The measuring system contains three parts, including mileage measurement, distance measurement and angle of the truck in order to record the antenna position along the tunnel. An ultrasonic distance measuring sensor is installed at the end of the upper

arm

to measure the distance between

the antenna and the tunnel surface. Moreover, the angle of the upper

arm

�

10

� � � �

15

Q;" E

measurement. An odometer is used to measure the mileage

20

grouting layer

can be recorded by an angle sensor so the

antenna position in the cross section of the tunnel can be determined.

35 TV. DATA ANALYSIS o

In this section, numerical simulations for survey lines

0.5

1.5

illustrated in Fig. 2 are carried out using FDTD method. By analyzing the simulation data, the adaptability of the two

2 Scan

2.5

axis(m)

3

4

3.5

Fig. 7. Simulation result for tunnel crown inspection

inspection method, mechanical and manual, are discussed. Taking

into

consideration

the

inner

structure

B. Tunnel Haunch

characteristic of the highway shield tunnel, simulations for the tunnel crown, for the sidewall and for the bottom are

Two

models

inspection

and

are

set

manual

up

considering

inspection

mechanical

respectively.

The

made respectively.

geometries of the models are identical. The outermost layer

A.

is a 30cm reinforced concrete side wall, behind which is a

Tunnel Crown A modelling is made to simulate mechanical inspection

of grouting layer from outside the tunnel flue. The physical model is presented in Fig. 6. The flue sheet with a thickness of lOcm is made of concrete. The height from the flue sheet to the tunnel lining is one meter and is filled with air. The tunnel lining is made of reinforced concrete and 80cm thick.

cable gallery with cables and the supports. Behind cable gallery is 80cm tunnel lining, 20cm grout (uneven) and the ground. Fig. 8 (a) simulates mechanical inspection from outside the side wall, and Fig. 8 (b) simulates manual inspection inside cable gallery just at the lining surface. ant�una5

Behind the lining, an uneven grouting layer is set up. The

moving dirwion

background medium is soil. alltl!lUlaS 0

moving direction

.....................

E1 �.

)

0.5

�

E

:sa.

t3

o

1 2

1.5

3

Oi�aoce(m)

5

0

Oi�aoce(m)

Fig. 8. Physical model for tunnel haunch inspection

2

The results are shown in Fig. 2.5

9, from which the

lining/grout layer interface and grout/soil interface can be o

0.5

1.5

2

2.5 3 Distance(m)

3.5

4

4.5

5

clearly recognized in Fig. 9 (b), while in Fig. 9 (a), the reflection of grout is relatively obscure because steel bars in the side wall and facilities in the gallery cause the EM wave

Fig. 6. Physical model for tunnel crown inspection The simulation result after processing is shown in Fig. 7. The flue sheet does not affect GPR signals much after

to scatter fiercely and cover the reflection from grouting layer.

suppressing multiples between flue sheet and lining. The lining/grout layer interface and grout/soil interface can be clearly recognized in the synthetic GPR image.

415

15th International Conference on Ground Penetrating Radar - GPR 2014

5

�

10 � �-...;;;,:. .....

� � � � �

15

., E

�

grout/soil interfaces can be clearly recognized in synthetic OPR image.

o 5

20 �-­ 25

grouting layer

-�

�

10

�

15

�

20

., E

30

�

o

the

Thus mechanical inspection for

tunnel bottom is feasible and can get a good result.

=.-...

o

�

The result in Fig. 11 shows the lining/grout layer and

(a) �

1.5

0.5

2 Scan

2.5

axis(m)

3

3.5

� � ;;:

4

25

o

�

30 35 o

1.5

0.5

2.5 2 Scan axis(m)

3

4

3.5

Fig. 11. Simulation result for tunnel bottom inspection v. CONCLUSION

For the highway shield tunnel, the large cross section and

multi

space

become

the

main

barriers

of

OPR

inspection for grouting behind segments, which makes the traditional manual detection way not meet this new situation. Therefore, a vehicle mounted integrated OPR equipment is designed to inspect the positions that man cannot reach. Scan

OPR inspections are simulated by FDTD method. The

axis(m)

Fig. 9. Simulation results for tunnel haunch inspections: (a) Mechanical inspection and (b) Manual inspection

results show that, in the tunnel crown, which is five or six meters high from the driveway, mechanical inspection from outside the flue sheet can be applied, and the grouting layer

C. Tunnel Bottom

is clearly seen from the OPR image; at the haunch, due to

Mechanical inspection for tunnel bottom is simulated. A

the side wall and the facilities in the cable gallery adversely

physical model is established as Fig. 10. The top layer is the

affect EM wave penetrating, manual inspection in the

tunnel pavement

gallery is a better choice than mechanical one from outside

made

of reinforced

concrete with a

thickness of 30cm. 60cm Below the pavement is the tunnel

the side wall; on the bottom, vehicle mounted inspection is

lining. Behind the tunnel lining is an uneven layer of grout

the most suitable way as the traffic need not to be

and the background medium is soil. antennas

interrupted during detection and the simulation shows a good result.

moving direction )

0.5

E :sa. �

ACKNOWLEDGMENT

....................�

o

The authors would like to acknowledge the fmancial support from the National Basic Research Program of China (973 Program: 2011CB013803), National Natural Science

1

Foundation of China (41372273), and Shanghai Science and Technology

1.5

Development

Funds

(12231200900,

l3231200102).

2

REFERENCES

2.5 o

2 3 Distance(m)

4

5

[1]

C. Thienert and M. Pulsforl. "Intluence of annular gap grout on shield tunnel lining bedding behavior", in Proc. 39th General

Fig. 10. Physical model for tunnel bottom inspection

Assembly

of

the

lnternational-Tunneling-and­

Underground-Space-Association, Geneva, Switzerland, May 2013, pp. 618-625.

416

15th International Conference on Ground Penetrating Radar - GPR 2014

[2]

S. Pelizza, D. Peila, R. Sorge, et al. "Back-fill grout with two

penetrating radar in the

component mix in EPB tunneling to

Journal of Geophysics and Engineering, Vol.4, pp. 253-261,

minimize

surface

settlements: Rome Metro-Line C case history", in Proc. 7th International

Symposium

on

Geotechnical

Aspects

of

Underground Construction in Soft Ground, Rome, Italy, May [3]

China",

Aug. 2007. [5]

L. Zhang, Z. P. Liu and C. M. Gong. 'The lining quality detection and grouting effect evaluation of the Kunlun

2011, pp. 291-299.

Mountain railway tunnel using ground-penetrating radar",

F. S. Zhang, X. Y. Xie and H. W. Huang. "Application of

Near Surface Geophysics, Vol. 6, pp. 175-180, Jun. 2008.

ground penetrating radar in grouting evaluation for shield tunnel construction", Tunneling and Underground Space [4]

Shanghai Metro Line,

[6]

X. Y. Xie, C. C. Zeng and Z. G.

Wang. "GPR signal

enhancement using band-pass and K-L filtering: a case study

Technology, Vol. 25, pp. 99-107, Mar. 2010.

for the evaluation of grout in a shielded tunnel", Journal of

X. Y. Xie, Y. J. Liu, H. W. Huang, et al. "Evaluation of

Geophysics and Engineering, VoLl 0, pp. 1-10, Jun. 2013.

grout behind the lining of shield tunnels using ground-

417