Based on engineering practices of four typical traffic immersed tunnels built in China, this paper details the features of the four dominant foundation treatment methods for immersed tunnel construction: pile foundation, sand flow foundation, grouting foundation, and gravel bedding foundation. Subsoil stress time-history of different method are specified first, plus a summary of settlement assessment method for foundation quality control. Further, a comprehensive comparison of settlement and cost of these four foundation treatment methods is conducted to highlights the specific merits, disadvantages and conditions encountered in each foundation treatment method, based on real projects information. The findings of this article could henceforth be applied to foundation treatment work in immersed tube tunnel construction.
. [J]. Frontiers of Structural and Civil Engineering, 2020, 14(1): 82-93.
Shaochun WANG, Xuehui ZHANG, Yun BAI. Comparative study on foundation treatment methods of immersed tunnels in China. Front. Struct. Civ. Eng., 2020, 14(1): 82-93.
small settlement even in soft foundation and high siltation conditions reduce uneven settlement when stiffness of the subsoil varied considerably along the tunnel line reduce settlement under the long-term vibration situation caused by large dynamic load
high cost difficult to adjust the pile heads to the same level
sand flow
no interference with navigation immune to the hydrogeology and meteorology lower requirement of the sand particle size compared to sand jetting method
strict restriction with siltation lifting of elements caused by high water pressure
grouting foundation
no interference with navigation immune to the hydrogeology and meteorology simple equipment with small investment easier to control grouting pressure and amount than sand flow method can be used in earthquake risky area
high requirement of mortar properties require real-time inspection of the grouting status
gravel bedding
no damage to concrete elements need no temporary supports in the trench smaller level tolerance can be achieved on the bed can be used in earthquake risky area
interfere with navigation high requirement and large investment in the equipment fabrication strict construction precision
Tab.2
Fig.2
Fig.3
Fig.4
Fig.5
Fig.6
parameters
values
pump power
37 kW
motor rotation speed
100–1375 m/s
injection rate
5 m3/s
diameter of pipe at entrance
8 inch
diameter of pipe at exit
6 inch
sand: water ratio
1:9–1:8
sand: cement clinker ratio
1:0.05
radius of sand deposit (minimum)
7.5 m
Tab.3
Fig.7
Fig.8
Fig.9
element
1
2
3
4
accumulated settlements
left-6.2
left-6.7
left-4.3
left-5.1
from September 2006 to October 2009 (mm)
right-5.8
right-3.0
right-2.3
right-2.9
Tab.4
Fig.10
Fig.11
Fig.12
Fig.13
section
western island section
western slope section
middle section
eastern slope section
eastern island section
elements
open and buried section
E33-E30/S4
E30/S4-E6/S2
E6/S2-E1
open and buried section
treatment method
PHC pile and HJG pile composite foundation
SCP composite foundation
gravel bedding foundation
SCP composite foundation
PHC pile and HJG pile composite foundation
Tab.5
Fig.14
project
Outer Ring Tunnel
Changhong Tunnel
Yongjiang Tunnel
Zhujiang Tunnel
purchasing method
D&B
D&B
traditional
traditional
construction duration
4 years
2 years
8 years
3 years
hydrogeology
serious siltation and soft ground
serious siltation and soft ground
serious siltation and soft ground
intermediary weathered rock ground
foundation type
sand flow
pile
grouting
sand flow
accumulative settlement
23 cm
2 cm
8.84 cm
3 cm
foundation cost (million RMB Yuan)
13.5
20
2.29
5
contract sum (billion RMB Yuan)
0.11
0.372
0.16
0.173
foundation/contract ration
1.22%
5%
1.40%
2.89%
Tab.6
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