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Synthetical Analysis on Monitoring of Wushaoling Railway Tunnel

Zhichun Liu, Wenjiang Li, Sumin Zhang, yongquan Zhu

School of Civil Engineering, Shijiazhuang Railway Institute, Shijiazhuang, China, 050043

ABSTRACT

Wushaoling railway tunnel, the longest single-track railway tunnel in China, is the key project of

Lanzhou-xinjiang railway line. It goes through four regional faults (F4-F7). The geological and

geostress conditions are quite complicated. According to the characteristics of soft rock tunnel with

large deformation on complicated stress condition, comprehensive monitoring is executed in

construction of Wushaoling tunnel. Based on the measured results of the crown settlement, the

horizontal convergence, the axial force of rock bolt, the surrounding rock pressure, the stress in steel

set, the stress in shotctete and the stress and pressure in the secondary lining, the relation between

surrounding rock pressure and displacement, the distribution rule of displacement, the coefficient of

lateral pressure, the shared ratio of secondary lining pressure, the construction time of secondary lining

etc, are analysed in this paper. The above information is feedback to the construction in time. The

structure stability is analysed and the corresponding measures are adopted. It can also provide the

numerical coefficients for data simulation and theoretical analysis. It is proved that the effect is

reliable, the surrounding rock is stable and the structure is in good condition, providing a reliable

technical guarantee for the perforation of the section.

1. INTRODUCTION

Monitoring plays an important role in design and construction of tunnels, since the diverse geology of

tunnel and the complicated interaction between surrounding rock and tunnel support. The purpose, on

the one hand, is to understand the goings of the surrounding rock and the support structure, to forecast

dangerous case and take measures accordingly, and on the other hand, is to accumulates data for other

analogous tunnels (Li Xiaohong (2002), Jiang Shuping et al.(2004), Yang Huijun et al.(2004)). The

monitoring should be strengthened especially in the soft rock tunnel with large deformation for which

there are no feasible measures in the current relative code for design and construction. There are many

inconsistencies between the code and the practice (Professional Standard (2001)). Many scholars have

studied on soft rock tunnels, and accumulated many experiences on the design and construction (He

Manchao et al. (2002), Zhang Zhidao (2003)). But few corresponding systematic monitoring data are

reported.

2. SURVEY OF PROJECT

Wushaoling railway tunnel, the longest single-track railway tunnel in China, lies in south section of

west Lanzhou –south Wuwei of Lanzhou-Xinjiang railway line. It consists of two single-track tunnels

(left line and right line) spaced 40 m. The right line, the main tunnel, is built through earlier, and the

left line is a parallel drift at first and enlarged to a main tunnel finally. The longitudinal gradient is

mainly 11 , and the altitude of inlet is 2663 m and the outlet is 2447 m, and the maximal depth of the

tunnel is 1100 m. It goes through four broad regional faults (F4-F7). The geological and geostress

condition are complicated.

2

Composite lining is adopted. Considering the fault activity and cracked rock, the circular cross-

section is used in F7 fault, and elliptical used in other places according to characteristics of each. In

F4-F7 regional faults, especially F4 fault region, Silurian slate with phyllite rock region and F7 fault

region, the surrounding rock is quite cracked,

and the tunnel stability is awfully bad. The

tunnel deformation is so large that collapse

appeared in few regions during the tunnel

construction.

The monitoring has been taken for over

one year since April 2004, consisting of axial

force of rock bolt, surrounding rock pressure,

stress in steel liner plate, shotcrete, and

secondary lining, secondary lining pressure, and

the settlement of arch crown, the horizontal

convergence, in F4 fault region, Silurian slate

with phyllite rock region and F7 fault region.

Fig. 1 shows the arrangement of observation

points.

3. MONITORING RESULTS

3.1 Deformation

Monitoring deformation, which can offer direct information for tunnel stability, is direct reflection of

reciprocity between the surrounding rock and the tunnel support. It consists of the settlement of arch

crown, horizontal convergence of spring of arch, middle of wall and footing of initial support, and

horizontal convergence of secondary lining. Table. 1 shows the statistical results of monitoring

deformation.

Table 1. Statistical results of measured deformation

initial support

total deformation(mm) max. deformation

rate (mm/d)

secondary

lining(mm)

region

line

site

max.

aver.

max.

aver. max. aver.

main zone

324.31

125.12

73.46

25.62 3.97 2.50

F4 fault

right line

influencing zone

343.10

91.87

58.58

19.55 3.41 1.98

phyllite mostly

932.45

422.97 165.33

80.65 10.06 4.66

Silurian slate with

phyllite rock

right line

slate mostly

473.91

211.25 122.05

38.72 17.40 4.55

initial stages

716.12

353.54 153.21

70.24

right line

after modification

310.51

124.87

79.65

30.76 23.00 2.70

initial stages

1209.38

831.01 167.53

87.54 21.53 0.16

F7 fault

left line

after modification

367.03

195.60

81.61

35.90 13.56 3.94

3.2 axial force of rock bolt

Through monitoring of axial force of rock bolt, the development of the tunnel deformation and the

limit of drop zone of surrounding rock strength can be estimated. And the effect of the bolt and

reasonability of the parameters for the bolt can be evaluated. Six measure bolts, 4-5m long, are

installed in every measuring profile with four measurement points on each bolt. As is shown in Table

2, the axial force of rock bolt is tension, and the depth of max. tension point is two to three meters

from tunnel wall.

Figure 1. Arrangement of observation points

horizontal convergence

tension in bolt

surrounding rock pressure

stress in shotcrete and

steel set

settlement of arch crown

stress and pressure in

secondary lining

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Table 2. Statistical results of measured axial force of rock bolt

region

line

max. tension(kN)

depth of max. tension point (m)

F4 fault

right line

97.4

main zone: 2.1~2.7, influencing zone: 1.4~2.1

Silurian slate with phyllite rock

right line

68.9

phyllite mostly: 2.1~3.4

right line

52.0

main zone: 2.1~3.4

F7 fault

left line

50.00

main zone: 2.7~3.7

3.3 support pressure

Support pressure includes the surrounding rock pressure and the secondary lining pressure. Table 3

illustrates the results of measurement support pressure.

Table 3. Statistical results of measured support pressure (MPa)

the surrounding rock pressure

the secondary lining pressure

region

line

max.

aver.

max.

aver.

F4 fault

right line

0.887

0.286

0.270

0.112

Silurian slate with phyllite rock right line

0.926

0.325

0.349

0.165

right line

0.952

0.381

0.663

0.211

F7 fault

left line

0.737

0.311

0.492

0.189

3.4 support stress

Support stress includes the sprayed coatings stress, the steel liner plate stress, and the secondary lining

stress. Table 4 illustrates the results of measurement support stress.

Table 4. Statistical results of measured support stress (MPa)

the sprayed coatings the steel liner plate the secondary lining

region

line

max.

av.

max.

av.

max.

av.

F4 fault

right line

12.83

5.41

160.65

104.45

9.88

5.89

Silurian slate with phyllite rock

right line

11.74

3.09

196.66

72.46

5.55

2.43

right line

16.21

6.78

9.26

6.08

F7 fault

left line

18.43

6.05

282.90

82.52

13.30

5.62

4. SYNTHETICAL ANALYSIS AND FEEDBACK OF MONITORING DATA

4.1 The rules and synthetical analysis of deformation

Figure 2 shows the relation

between the total deformation

and the max. deformation rate

of initial support, and the

deformation

of

secondary

lining in Silurian slate with

phyllite rock region. In order to

compare conveniently, the Y-

coordinate

is

logarithm

coordinate. Figure 2 shows

rules as follows.

(1) The deformation of initial

support in most phyllite region

is bigger than in most slate

region.

0.01

0.1

1

10

100

1000

YDK175+000

YDK175+200

YDK175+400

YDK175+600

YDK175+800

mileage

de

fo

rm

at

io

n/

m

m

initial support deformation
final lining deformation
maximum of initial support deformation rate

most slate

most phyllite

Figure 2. The distribution rules of deformation in Silurian slate

with phyllite rock region

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(2) The total deformation of initial support increases with the of the max. deformation rate of initial

support.

(3) The relation between deformation of initial support and secondary lining is not obvious.

4.2 The analysis of lateral pressure coefficient

Lateral pressure coefficient, which is an important parameter in action-reaction calculation model, is

the direct reflection to the result of initial geostress re-distribution after the tunnel construction. It can

be worked out by the statistic analysis of the monitoring support pressure. It can be shown using the

following equations:

V

H

P

P

=

l

(1)

where

l

is the lateral pressure coefficient; and

H

P

is the horizontal vector of the surrounding rock

pressure of tunnel wall; and

V

P

is the vertical vector of the surrounding rock pressure of tunnel arch.

The Statistical results of lateral pressure coefficient are shown in Table 5.

4.3 The shared ratio of secondary lining pressure

The shared ratio of secondary lining pressure, which is also an

important parameter in action-reaction calculation model, is a

popular topic in tunnel fields. It impacts on the stress and the

stability of the secondary lining. The ratio can be worked out by

the statistic analysis of the monitoring pressure of initial support

and secondary lining, and can be shown using the following

equations:

100%

™

=

F

S

P

P

m

(2)

where m is the shared ratio of secondary lining pressure; and

S

P

is the statistical monitoring pressure of secondary lining; and

F

P

is the statistical monitoring pressure of initial support.

The Statistical results of the shared ratio of secondary lining

pressure are shown in Table 5. And

Figure 3 illustrates the shared ratio

distribution along contour line. It can be

seen the shared ratio of secondary lining

pressure on tunnel wall is bigger than

that on arch.

4.4 The relation between the surrounding rock pressure and the displacement

Theoretically, the relation between the surrounding rock pressure and the displacement can be

illustrated by the ground and support reaction curve in convergence-confinement model, which is

illustrated in Figure 4 (Jing Shiting et al. (2002)). The curve is the typical soft ground reaction

curve. The curve is support reaction curve, which is intersected with curve at point A, showing

balance of the ground pressure and the support reaction. If the stiffness of the support becomes bigger,

the intersection point is B, showing a greater support reaction as curve . If the support is applied too

late, the ground will become loose and collapse will occur as in curve . In practice, the ground

reaction curve is difficult to draw because of various reasons. But the support reaction curve can be

drawn with the monitoring pressure and deformation of support. In Figure 5, X-coordinate is

horizontal convergence of support, and the upper Y-coordinate is monitoring ground pressure, and the

Figure 3. Shared ratio distribution

along contour line for secondary

lining pressure in right line of F7

fault

31.1%

25.2%

14.2%

56.3%

48.9%

55.2%

60.2%

39.9%

29.3%

initial support final lining

Table 5. Statistical result of

l

and m

region

line

m

F4 fault

right line

0.842

32.2%

Silurian slate with phyllite rock

right line

0.967

28.2%

right line

1.563

39.7%

F7 fault

left line

1.251

44.2%

5

lower Y-coordinate is time. It shows the actual support reaction curve of arch spring and middle of

wall of YDK170+610 section, and illustrates the pressure-deformation curve and deformation-time

curve. Furthermore, it can forecast the relevant deformation to pressure relying on pressure-

deformation curve, i.e. 109.902 mm (spring of arch) and 235.209 mm (middle of wall). It can also be

shown, compared between spring of arch and middle of wall, that the former has bigger pressure and

less deformation.

Regarding the forecast deformation and the final pressure as stable data, the dimensionless

development correlation between the surrounding rock pressure and horizontal convergence of middle

of wall is worked out in Figure 6. It can be seen that ground pressure grows more slowly than

deformation.

G

4.5 Construction time of secondary lining

Comparing between the soft-rock and rigid-rock,

the former has less elastic modulus and strength.

Therefore, the deformation in soft-rock tunnel is much

larger than in rigid-rock tunnel, and the time of lining

construction of soft-rock tunnel should not be confined

within limit of 0.2mm/d as in the code. If the limit was

applied mechanically, the time of lining construction

should be delayed, and the deformation cannot be

controlled easily, and too large deformation can bring

collapses. In addition, it is wasteful using stronger

rigid support to decrease deformation, and it is feasible that lining is constructed earlier to bear partial

loading in soft-rock tunnel.

The construction time of secondary lining of Wushaoling tunnel in situ is shown in Table 6.

Table 6. The construction time of secondary lining

classification of large deformation

items

general deformation

U

M

/B

<3%

3% 5%

5% 8%

8%

U

R

/ U

L

80%~90%

70%~80%

65%~75%

60%~70%

U

M

/ U

L

55%~62%

47%~55%

43%~51%

39%~47%

V

F

/U

M

<0.5%

0.5%~1.0%

0.5%~1.5%

0.5%~2.0%

Notes: where U

M

is monitoring deformation, and B is tunnel width, and U

L

is limit deformation after initial support construction, and U

R

is the

actual deformation emerged before lining construction, and V

F

is deformation rate before lining construction. Because of the actual deformation (U

R

)

consist of not only the monitoring deformation (U

M

), but also the elastic deformation and the lost deformation in measure, the U

R

is larger than U

M

.

And U

L

can be worked out according to calculation and monitoring of each region.

5. CONCLUSION

Figure 4. Convergence/confinement curve

P

i



r



0

O

u

r

B A

C

D

E

Figure 5. Test initial support reaction curve

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0

50

100

150

200

250

u

r

(mm)

P

i

(M

Pa

)

P=0.0509exp(0.0075u)

R

2

=0.9306

P=0.0863exp(0.0119u)

R

2

=0.9239

5

10
15
20
25

t (

d)

spring of arch
middle of wall

inverted arch

0

20

40

60

80

100

0

10

20

30

T (d)

ra

te

(%

)

deformation

ground pressure

Figure 6. The dimensionless development

correlation of the ground pressure and

deformation

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(1)The tunnel deformation is very large, and the max. horizontal convergence reacheso 1209.38 mm

in left line of F7 fault, and the max. deformation rate is 167.53mm/d. The tunnel displays all signs of

large deformation tunnel, i.e. large deformation, high early deformation rate, and long duration. The

max. lining deformation is 13.30 mm. The deformation in initial construction stage is large. But after

modification of design and construction, the deformation has been controlled to a certain extent.

(2)The rock bolts are all in tension, and the depth of max. tension point is two to three meters from

the tunnel wall, which shows the bolt length is reasonable.

(3)The max. surrounding rock pressure is 0.952 MPa , the max. lining pressure is 0.663 MPa, and

the support pressure of arch is larger than of wall. The max. lateral pressure coefficient is 1.563, the

min is 0.842. The max. of the shared ratio of secondary lining is 44.2%, the min is 28.2%. The lining

bears partial loading.

(4)The max. of the stress of the steel liner plate is 282.90 MPa, and the max. of shotcrete stress is

18.43 MPa, and the max. of lining stress is 13.30 MPa. None of these data exceeds limit strength of

their material.

(5)The monitoring data in main fault zone is larger than in influencing fault zone, and the

monitoring data in most phyllite region is larger than in most slate region. Therefore, different support

parameters should be adopted in different region according to measure data.

(6)In large-deformation tunnel region, the construction time of secondary lining should be rectified

according to the measure deformation.

In conclusion, after modification of design and construction, tunnel deformation has been controlled

to a certain extent, and the structures of support and lining are stable. The measure has provided the

scientific basis of the modification of support parameter and the construction time of secondary lining,

and has offered calculation parameters. The results have given the basis data for subsequent research,

and have accumulated experience of design and construction of very long tunnel on complicated

geostress condition.

REFERENCES

He Manchao, Jing Haihe and Sun Xiaoming, 2002. “Research progress of soft rock engineering

geomechanics in China coal mine”. Journal of Engineering Geology, China, 8(1), pp. 46~62.

Li Xiaohong, 2002. “The NATM of Tunnel and Monitoring Technology”, Beijing: Science Press,

China.

Jiang Shuping and Zhao Yang, 2004. “Study on monitoring and Back Analysis ofr road tunnel with

Complex Geology. Chinese Journal of Rock Mechanics and Engineering” 23(20), pp. 3460-

3464.

Jing Shiting, Zhu Yongquan and Song Yuxiang, 2002. “Tunnel structure reliability”. Beijing: China

Railway Publishing House, China.

Professional Standard Compilation Group of People’s Republic of China, 2001. “Code for design of

railway tunnel”(TB 10204-2002). Beijing: China Railway Publishing House, China.

Professional Standard Compilation Group of People’s Republic of China, 2001. “Code for

construction on tunnel of railway”(TB 10003-2001). Beijing: China Railway Publishing House,

China.

Yang Huijun, Hu Chunlin and Chen, Wenwu, 2004. “Information Construction of the Tunnel in a

Fault and Crush Zone”. Chinese Journal of Rock Mechanics and Engineering” 23(22), pp. 3917-

3922.

Zhang Zhidao, 2003. “Discussion and study on large deformationg of tunnel in squeezing ground”,

Modern Tunneling Technology, 40(2), China, pp. 5~12.