Monitoring and Analysis of High Altitude Wetland Tunnel

Monitoring and Analysis of High Altitude Wetland Tunnel
XIONG Junnan, WANG Zegen
School of Civil & Architecture Southwest Petroleum University, Chengdu, China, 610500
[email protected]
Abstract: Take bodhisattva hillock Wetland tunnel with an example, this paper introduces monitoring
and measurement items and method in the New Austrian Tunneling Method construction process.
Analysis the deformation and mechanical characteristics of surrounding rock and initial supporting
about High altitude wetland tunnel, and the monitoring results are analyzed, which provides reference
for similar engineering analysis.
Keywords: Tunnel, New Austrian Tunneling Method, Monitoring and measurement, wetland tunnel
The engineering excavation in rock is the behavior of rock mass destruction, which destruction of the
rock relative balance has been achieved and the lowest energy state, so that the stress field change,
resulting in the release and transfer of energy, causing stress redistribution, and changes rock stress
boundary conditions and displacement boundary conditions, which can produce rock deformation and
destruction [2]. High-altitude wetlands tunnel has the Characteristic of rich groundwater and surface
water, Very long, excavation section is very large etc, tunnel geologic hazards such as hard rock burst
and large deformation of soft rock will be occurred after excavation. So research of surrounding rock
deformation distribution about High-altitude wetlands tunnel has important significance in complex
geological conditions of tunnel excavation and support.
1 Project Overview
The bodhisattva hillock tunnel which in construction is a wetlands tunnel across the Tuowu mountain in
the highway of Yaan to Lugu city. The left and right hole of bodhisattva hillock tunnel are located on the
curve, the left line start and end mileage K170 +390 ~ K173 +350, length 2960m, hole design elevation
to 2427.15m and 2438.93m, the right line start and end mileage YK170 +365 ~ YK173 +345, tunnel
length 2980m, hole design elevation to 2426.86m and 2438.89m.
The start part of right hole in Bodhisattva hillock tunnel has construction about 100 meters, of which
V-class rock 100m. The area of tunnel addresses for quaternary strata lithology major new series diluvial
layer, the distribution of the Yaan partial tertiary yesterday at group shaly, Figure for the early sinian
hole near section of granite, for strong weathering. Tunnel site influenced by the tranquil River fault
zone, the hole itself through F1 ~ F4 fault. Main overburden groundwater pore water and fissure water,
fault and its impact with the medium or high permeable layer; surface water mainly in the right side of
Hai Zi, the water level above the tunnel level. The tunnel site area is abundant in rainfall and snow
covered in winter, mountain vegetation development, vertical and horizontal gentler slopes, rain and
mountain snow melt water to seep into the groundwater development. Deformation of rock easily
collapse comes as the rainy season, with the emission of water and sand, or even collapse to the surface,
severely affected to the construction. Therefore, during the tunnel construction site monitoring will
obtain first-hand data processing and analysis, timely feedback to design and construction, to adjust the
parameters, the design and construction of great significance.
2 Monitoring Items and Methods
2.1 Monitoring items
According to the design documents of bodhisattva hillock tunnel, reference standard tunnel and the
guide of New Austrian Tunneling Method, monitoring items includes: geological and supporting
714
conditions observations, Tunnel surface subsidence monitoring, Vault sink monitoring, surrounding
internal displacement monitoring; surrounding convergence monitoring. Monitoring method of each
monitoring items are shown in Table 1.
Sequence
number
The item name
Table1: Measurement contents and method
Instrument
Layout section
1
geological and supporting
conditions observations
2
surrounding convergence
monitoring
3
Vault sink monitoring
4
5
Geological compass
SWJ—4Tunnel
convergence
Total station
SWJ—4 Tunnel
convergence
Level
Tunnel surface subsidence
Level Indium steel rule
monitoring
surrounding internal
SDW Multi-point
displacement monitoring
displacement meter
、
、
Monitoring point
number
Excavation After the initial
support
，
Interval 10~50m add point Each section 3 or
to Portal
5 points
，
Interval 10~50m add point Each section 3 or
to Portal
5 points
In or out of the hole
Each section7 points
As two holes
4 points per hole
2.2 The implementation of monitoring measurement
Tunnel surrounding convergence and vault sink are the Comprehensive embodiment of Rock dynamic,
Rock condition, Supporting effect. The measurement results can be used to judge the stability of
surrounding rock and appropriateness of Initial support, perfusion opportunity of lining and inflected
arch etc. The tunnel shallow surface subsidence monitoring is an important basis to determine the
surface stability of shallow tunnels, so this three items are the key of monitoring.
The entrance of Bodhisattva hillock tunnel is a V-class rock, water content are large, geological
conditions are poor, in order to ensure security of construction, layout surrounding convergence and
subsidence monitoring vault section every 10m each group. And step by step using upper and lower
excavation construction method, it is at the upper and lower level layout 1-2, 4-5, two level lines, as
shown in Figure 1. Meanwhile, in the shallow part of hole entrance, every 10m along the tunnel axis
layout subsidence monitoring sections, each section composed of the 7 points and 1 basis point to
monitor the composition, arrangement shown in Figure 1.
Tunnel monitoring frequency in accordance with the "road tunnel construction specifications" in the
time between the request to monitor laid the monitoring section for monitoring, some special deformed
cross section, appropriate Increase the number of observations.
3 Monitoring Results and Stability Analysis
Since we began to carry out monitoring work from May 2008, a large number of monitoring data has
been collected in accordance with the monitoring method described above. While describing the
relevant monitoring results, this paper focuses on the right line of the import section of the tunnel roof
leak occurs, severe deformation of section steel support case, select typical monitoring sections to
analysis.
715
Monitoring base
point Subsidence
2~5m Spacing
3
B
C
E
F
A
1
2
5
D
4
m
5
.
1
Fig.1 Measuring points and line arrangement on section
3.1 Peripheral displacement and vault subsidence measurement
Through almost 50 days' peripheral displacement and vault subsidence measurement for right side of
bodhisattva hillock wetland tunnel, a time-dependent curves of horizontal convergence deformations
and crown settlements is finally drawn out as follows (Fig.2), whose original data are handled by excel.
Peripheral convergence occurs when the data is positive; peripheral expansion occurs when it is negative.
Figure 3 is speed- time-dependent curves of horizontal convergence deformations and crown
settlements.
f
o
e
u
l
a
v
l
a
t
o
T
25
20
15
10
5
2. 5
)
m
m
(
e
c
n
e
g
r
e
v
n
o
c
)
d
/
m
m
(
e
g
n
a
h
c
f
o
e
t
a
R
Data(08-m-d)
0
5-3
5-8
5-13
5-18
5-23
5-28
6-2
6-7
6-12
6-17
2
1. 5
1
0. 5
0
1
- 0. 5
Fig.2 Time-dependent curves of horizontal convergence
deformations and crown settlements
3
5
7
9
11
13
15
17
19
21
23
25
27
Time(d)
Fig.3 Surrounding rock deformation rate curve
The analysis of time-dependent curves of horizontal convergence deformations and crown settlements
is that when the value of the vault subsidence of a certain section is much larger than that of horizontal
convergence it is indicating the impact of the surrounding rock deformation is mainly from the top of the
section; changes tended to be stable after about 25 days laying of the section of the level of convergence
curve (the figure of a scale equals 5 days), and vault subsidence curve, after 35 days of laying, levels off.
These two conditions indicates that changes tended to be stable after the section excavation and after
about 40 days' facilities of the initial stabilization for the support.
Comparison between peripheral convergence rate curve and vault subsidence rate curve shows vault
subsidence rate is larger than that of horizontal convergence. Horizontal convergence rate decreases
constantly since the laying-out of section, and after about 25 days, the rate gradually tends to zero. Vault
settlement curve shows the same trend, after about 35days gradually to zero.
3.2 Analysis of subsidence data
Tunnel Left, Right Line shallow subsidence were separately laid two sections YK170 +375, YK170
+385, each section laying 7 points of measurement, the sinking value of the vertical distribution of the
correspondent monitoring points are shown in Figure 4, and time-dependent curves of closing to the
surface subsidence of vault point are shown in Figure 5. After long-term monitoring, the right line of the
inducer has a large amount of surface subsidence accumulatively, with faster sinking rate and the
716
occurrence of the phenomenon of roof leaking. After timely feedback of the monitoring data, the design
and construction units took appropriate treatment measures.
Pointment 2 of YK370+375 Section
200
Total value of subsidence mm
）
)
（mm(150
200
)
m
m
(
e
c150
n
e
d
i
s
b
u100
s
e
v
i
t
a
l 50
u
m
u
C
0
YK370+385 Section
YK370+375 Section
1
2
3
4
Point number
5
6
7
Fig.4 The two section of surface subsidence
K111+150拱顶点
K111+130拱顶点
值
沉
下
计
累
100
50
Point 1 of YK370+385 Section
0
5月31日
6月20日
7月10日
7月30日
日期(08-m-d)
时间(d)
Date
8月19日
9月8日
Fig.5The surface subsidence monitoring accumulative value
From subsidence of horizontal distribution of each measuring point of the two sections, the point near
the middle of the tunnel is sinking in large quantities, and the farther the point is from the tunnel center
line, the smaller the subsidence is, which show shallow surface suffer an obvious influence from
construction disturbance; at the same time, section YK170 +375 points sink much greater than points of
section YK170 +385, which means the measuring points of surface subsidence is associated with
distance from hole. From the figures above, it shows that the farther from the hole, the smaller the
subsidence is.
Two monitoring points in all sections all went through a long period of change. From the surface
subsidence curves, since the layout of points in section YK170 +375, the curve tended to be stable after
about 70days, although some fluctuations occurred with continue monitoring, the fluctuation range is
small, which can be owing to a measurement error. Thus, this revealed the section tended to be basically
stable. SectionYK170 +385, after 60 days of layout, the curve was apt to be flattened, with a small
amount of sinking, which indicated that the section had also been inclined to be stabilized.
3.3 Stability analysis
Based on the data distribution of scatter graph, we can find out displacement variation rules applying
mathematical method to make a regression analysis. We still predicted the maximum. Multiple linear
regression with a matrix can be read: y = xβ + ε (1)
y is N dimension deflection's observation vector, y = ( y1 , y2 ,... yN )T ;
x is a N ( P + 1) matrix,
and its elements can be accurately measured or controlled to general observed value or their functions.
β is a parameter to be vector, β = ( β 0 , β1 ,...β p )T . ε
2
to the same normal distribution N (0, σ ) , and
T
−1
β
is a N dimensional random vector subject
's guess value
b can be obtained by the least
T
b = ( x x) x y (2)
T
T
−1
There is C = ( x x ) , then we get b = Cx y , and take the guess value b into formula 1, there will
be ŷ = xb .
square principle,
Take section YK170 +390 vault sinking data for example, and there is regression equation of vault
-0.8407
t
subsidence observation data: y = 21 . 381 × e
1
From the regression equation (1), take t = ∞ and the vault sinking final value can be obtained
y=21.38mm
-0.6365
t
2
Level of observation data convergence regression equation y = 15 . 873 × e
Take t = ∞ from the regression equation, the convergence final value of horizontal displacement can
be obtain y=15.873mm..
According to technical specifications of highway tunnel, vault, and the surrounding deformation can be
（）
（）
717
②
①
applied when the following conditions are met for secondary lining: displacement produced reached
more than 80% to 90% of the estimated total displacement.
the around displacement rate is less than
0.1 ~ 0.2mm/d or vault settlement rate is less than 0.07 ~ 0.15mm/d.
4 Conclusion
(1) The New Austrian Tunneling Method monitoring and measuring in high altitude wetlands tunnel
construction is of particular importance, and measurement data can be better reflected in the
deformation of surrounding rocks.
(2) Wetland tunnels are rich in groundwater and surface water, in the process of tunnel construction,
geological disasters are likely to be caused. Therefore, according to the site situation monitoring
frequency can be increased appropriately, and timely design feedback is effective to forecast
dangerous situation to ensure construction safety.
References
[1]. LI Ji-bo, QIAO chun-sheng. Monitoring and Analysis on Water-rich soft rock tunnel[J], Subgrade
Engineering,2006(6),76-77. (in Chinese)
[2]. yang hui-jun. deformation characteristic of tunnel surrounding rock under complex conditions[j].
journal of railway engineering society. 2006(1), 57-60. (in Chinese)
[3]. GUAN Hui-ping, X IONG Jun-nan. Deformation Monitoring of Surrounding Rocks and Stability
Analysis of Approximate Horizontal Rock Tunnel[J]. ROCK AND M INERAL ANALYSIS,
2008(5),357-362. (in Chinese)
[4]. The institute of survey and design of highway planning reference, Hunan Provincial
Communications Department, Ya'an to Lugu Expressway Section 23 of the contract construction
design in two stages[R].ChangSha, The institute of survey and design of highway planning
reference, Hunan Provincial Communications Department,2007.(in Chinese)
718