1
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
3
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
4
(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
6
(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
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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-
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Jing Shiting, Zhu Yongquan and Song Yuxiang, 2002. “Tunnel structure reliability”. Beijing: China
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Professional Standard Compilation Group of People’s Republic of China, 2001. “Code for design of
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