1. Key Laboratory of Transportation Tunnel Engineering, Ministry of Education, Southwest Jiaotong University, Chengdu 610036, China 2. Guangdong Provincial Railway Construction Investment Group Co., Ltd, Guangzhou 510080, China
Metro shield tunnels under the lateral relaxation of soil (LRS) are susceptible to significant lateral deformations, which jeopardizes the structural safety and waterproofing. However, deformation control standards for such situations have not been clearly defined. Therefore, based on a specific case, a model test is conducted to realize the LRS of a shield tunnel in a sandy stratum to reveal its effect on segment liners. Subsequently, a deformation control criterion is established. The LRS is simulated by linearly reducing the loads applied to the lateral sides of the segment structure. During lateral unloading, the lateral earth pressure coefficient on the segment decreases almost exponentially, and the structural deformation is characterized by horizontal expansion at the arch haunches and vertical shrinkage at the arch vault and arch bottom. Based on the mechanical pattern of the segment structure and the acoustic emission, the deformation response of a segment can be classified into three stages: elastic and quasi-elastic, damage, and rapid deformation development. For a shield tunnel with a diameter of approximately 6 m and under the lateral relaxation of sandy soil, when the ellipticity of the segment is less than 2.71%, reinforcement measures are not required. However, the segment deformation must be controlled when the ellipticity is 2.71% to 3.12%; in this regard, an ellipticity of 3% can be used as a benchmark in similar engineering projects.
standard value of uniaxial compressive strength (MPa)
32.4
1.62
1.53
circumferential main reinforcement
equivalent tension and compression stiffness (N)
2.4e9
1.53e5
1.8e5
Tab.5
Fig.5
Fig.6
bending type
bending stiffness (N?m/rad)
prototype groove depth (m)
model groove depth (mm)
groove position
positive bending
1.21 × 108
0.10
5
internal groove
negative bending
0.922 × 108
0.14
7
external groove
Tab.6
Fig.7
tunnel type
number of longitudinal bolts
elastic modulus (MPa)
length (mm)
diameter or width, thickness (mm)
prototype tunnel
16
2.06 × 105
400
30 (diameter)
model tunnel
16
450
10
10 (width); 2 (thickness)
Tab.7
Fig.8
Fig.9
No.
data name
measuring cells
position
1
radial convergence of segment
custom-developed displacement gauge
arch vault-arch bottom; between arch haunches (Fig.10)
2
internal force of segment
resistance strain gauge
inside and outside of segment (Fig.11)
3
earth pressure
earth pressure cell
outside of segment (Fig.12)
4
acoustic emission characteristics
acoustic emission device
arch vault, arch bottom, and arch haunches (inside of segment) (Fig.13)
Tab.8
Fig.10
Fig.11
Fig.12
Fig.13
loading step
depth of equivalent prototype tunnel (m)
depth of model tunnel (m)
vertical uniform load (kPa)
horizontal uniform load (kPa)
vertical oil pump pressure (MPa)
horizontal oil pump pressure (MPa)
1
10.0
0.500
10.0
2.93
2.0
0.4
2
10.0
0.500
10.0
5.87
2.0
0.8
3
15.0
0.750
15.0
5.87
3.0
0.8
4
15.0
0.750
15.0
8.80
3.0
1.2
5
20.0
1.000
20.0
8.80
4.0
1.2
6
20.0
1.000
20.0
11.74
4.0
1.6
7
22.5
1.125
22.5
11.74
4.5
1.6
8
22.5
1.125
22.5
13.20
4.5
1.8
9
25.0
1.250
25.0
13.20
5.0
1.8
10
25.0
1.250
25.0
14.67
5.0
2.0
Tab.9
loading step
depth of equivalent prototype tunnel (m)
depth of model tunnel (m)
vertical uniform load (kPa)
horizontal uniform load (kPa)
vertical oil pump pressure (MPa)
horizontal oil pump pressure (MPa)
10
25
1.25
25
14.67
5
2.0
11
25
1.25
25
13.20
5
1.8
12
25
1.25
25
11.74
5
1.6
13
25
1.25
25
10.28
5
1.4
14
25
1.25
25
8.80
5
1.2
15
25
1.25
25
5.87
5
0.8
16
25
1.25
25
2.93
5
0.4
17
25
1.25
25
0.00
5
0.0
Tab.10
Fig.14
Fig.15
Fig.16
Fig.17
Fig.18
Fig.19
Fig.20
Fig.21
Fig.22
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