1. Key Laboratory of Coastal Civil Engineering Structure and Safety of Ministry of Education, Tianjin University, Tianjin 300072, China 2. Department of Civil Engineering, Tianjin University, Tianjin 300072, China 3. Shanghai Tunnel Engineering Construction Co., Ltd., Shanghai 200032, China 4. Tianjin Municipal Engineering Design & Research Institute, Tianjin 300392, China
The pipe roofing method is widely used in tunnel construction because it can realize a flexible section shape and a large section area of the tunnel, especially under good ground conditions. However, the pipe roofing method has rarely been applied in soft ground, where the prediction and control of the ground settlement play important roles. This study proposes a sliced-soil–beam (SSB) model to predict the settlement of ground due to tunnelling using the pipe roofing method in soft ground. The model comprises a sliced-soil module based on the virtual work principle and a beam module based on structural mechanics. As part of this work, the Peck formula was modified for a square-section tunnel and adopted to construct a deformation mechanism of soft ground. The pipe roofing system was simplified to a three-dimensional Winkler beam to consider the interaction between the soil and pipe roofing. The model was verified in a case study conducted in Shanghai, China, in which it provided the efficient and accurate prediction of settlement. Finally, the parameters affecting the ground settlement were analyzed. It was clarified that the stiffness of the excavated soil and the steel support are the key factors in reducing ground settlement.
. [J]. Frontiers of Structural and Civil Engineering, 2023, 17(12): 1934-1948.
Yu DIAO, Yiming XUE, Weiqiang PAN, Gang ZHENG, Ying ZHANG, Dawei ZHANG, Haizuo ZHOU, Tianqi ZHANG. A 3D sliced-soil–beam model for settlement prediction of tunnelling using the pipe roofing method in soft ground. Front. Struct. Civ. Eng., 2023, 17(12): 1934-1948.
power for the stress-level dependency of stiffness (m)
0.65
–
Tab.1
Fig.1
Fig.2
Fig.3
Fig.4
Fig.5
Fig.6
Fig.7
Fig.8
item
parameter
value
unit
tunnel
height (H)
7.6
m
width (L)
7.5
m
overlying soil layer (C)
5.4
m
steel pipe
outer diameter ()
1600/1000
mm
inner diameter ()
1560/960
mm
density ()
7850
kg/m3
elastic modulus (E)
206
GPa
poisson’s ratio ()
0.3
–
Tab.2
soil
(° )
fill soil
17.3
24
16.5
4.92
0.30
silty clay-1
18.6
22
23.1
5.15
0.32
silty clay-2
17.3
10
17.3
3.34
0.33
mucky clay
18.4
12
13.5
2.43
0.37
Tab.3
Fig.9
Fig.10
Fig.11
item
parameter
value
trial tunnel section shrinkage
(%)
0.05
soil stress and strain
(kPa)
varies with depth (see Eq. (14))
0.15
1
latticed improvement stiffness
(MPa/m)
90
layered improvement stiffness
(MPa/m)
50
inner support stiffness
(MPa/m)
500
Tab.4
Fig.12
Fig.13
Fig.14
Fig.15
variable
value
(MPa/m)
35, 70, 90, 105, 140
(MPa/m)
Tab.5
Fig.16
Fig.17
variable
value
(MPa)
200, 350, 500, 650, 800
Tab.6
Fig.18
Fig.19
constant in displacement equations
general stiffness matrix of the beam
constant in displacement equations
effective cohesion
undrained shear strength of the soft ground
thickness of the overlying soil layer
diameter of pipe i
outer diameter of a pipe
inner diameter of a pipe
diameter of the circular-section tunnel
diameter of the equivalent tunnel
pipe elastic modulus
soil compression modulus
reference secant shear modulus
reference oedometer modulus
reference unloading–reloading modulus
reference shear modulus at very low strains
height of the square-section tunnel
settlement trough width
foundation reaction coefficient
latticed improvement stiffness
layered improvement stiffness
inner steel support stiffness
foundation stiffness matrix that is a combination of and
coefficient of earth pressure at rest
parameter in the Peck formula
width of the square-section tunnel
power for the stress-level dependency of stiffness
reference pressure
equivalent supporting pressure from the pipe roofing
earth pressure on the pipe roofing
force acting on node i
failure ratio
maximum ground settlement
soil volume loss
tunnel section shrinkage
trial tunnel section shrinkage
displacement of each beam
depth below the ground face
central depth of the tunnel
maximum depth of the mechanism
parameter controlling the shape of the mechanism
power exponent of the stress–strain power curve
effective internal friction angle
shear strain corresponding to 0.7G0ref
shear strain
shear strain at maximum shear strength
Poisson’s ratio of a pipe
Poisson’s ratio of unloading and reloading
Poisson’s ratio of the soil
unit weight of the soil
density of a pipe
shear strength
dilation angle
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