Structural Performance of Immersed Tunnel Element at Flexible Joint. Jian Sun Tongji University August 4, 2015

Transcription

1 Structural Performance of Immersed Tunnel Element at Flexible Joint Jian Sun Tongji University August 4, 2015

2 Immersed Tunnel Fit for underwater transportation passage project Prefabricated tunnel tube floated to construction site, sank and connected Shallow buried Prefabricated instead of constructed in site, light field construction work, high quality 2

3 Immersed Tunnel Tunnel tubes prefabricated in dry docks Tunnel tubes floated and transported to construction site 3

4 Immersed Tunnel Tubes in place lowered one at a time into a trench pre-dredged and connected to the previous tube 4

5 Connection of Immersed Tunnel Rigid Joint, connect two adjacent tunnel tubes as a whole through construction measures, high rigidity, well transmit all interactions, high internal force, limited joint deformation, Fit for short distance immersed tunnel Flexible Joint, limited connection mainly to restrict relative displacement between tubes, offer considerable joint flexibility, low internal force, Fit for long distance immersed tunnel 5

6 Flexible Joint Extended shell GINA gasket Prestress Anchor Element tube Element tube OMEGA gasket Fire barrier Shear key Schematic Drawing of Flexible Joint Tube Shear key Extended shell Cross Section of Tube at Element Joint 6

7 Flexible Joint 7

8 Flexible Joint Characteristic Connected mainly by shear key, no rigid connection Mainly transmits vertical and longitudinal load Relatively low joint rigidity Better bear settlement or earthquake Vertical load transmitted through shear key Longitudinal load transmitted through tunnel end structure 8

9 Study on Flexible Joint Precise model as part of a total tunnel model, study the local structural performance under dynamic force. Liu et al. (2011), Anastasopoulos et al. (2007), Liu (2014) etc. Numerical model universal for immersed tunnel analysis, Yu et al. (2014), Liu et al. (2014) etc. 9

10 Extended Shell End of tunnel tube at element joint Weakened area for installation of water proof and other facilities Mainly transmits longitudinal load, transmits limited vertical load and moment 10

11 Extended Shell 11

12 Characteristic of Extended Shell Sectional dimension relatively small Poor rigidity Substructure Part of flexible joint Mainly transmit longitudinal load, transmit limited vertical load and moment (which are main interaction between tunnel elements). Mainly bears water pressure 12

13 Project Background Deeply buried (maximum 44m under sea level) Flexible joint Severe siltation condition (0.5m/month in 2010, maximum thickness 20m) 13

14 Analysis Case (1)The element sunk in place In this case, two adjacent elements are pulled together for joining. In the space between two bulkheads, there is a little water trapped, still at the pressure corresponding to depth. There is longitudinal water pressure on both sides of the newly submerged element. The GINA gasket is not compressed and cannot provide waterproof. The joint is unfinished. (2) Depressurize & Backfill In this case, the water trapped between two adjacent elements is pumped. The water pressure on the other side of the newly located element pushed the element towards the previous one, and the gasket is pressed in the joint. A layer of 2m thick gallet is then backfilled to provide protection. The construction of an element is completed. 14

15 Analysis Case (3)Service Condition When the whole tunnel is completed, no bulkhead is exposed in water, and there will be no longitudinal water pressure on elements. When the siltation terminates, the silt above the tunnel will be 20.53m thick. (4)Ultimate Condition The ultimate condition is set on basis of service condition, and considers all unfavorable loads, including waves, rising of sea level and sunken load. 15

16 Analysis Analysis Object:roof Software :ANSYS Load:Water pressure, etc. Interaction between tubes not included Analysis Method:Static 16

17 Schematic Diagram of Loading Accidental Load, Wave &Change of sea level Water pressutre & Earth pressure Water pressutre Live load Gravity Earth pressutre Water pressutre & Reaction of foundation 17

18 Analysis Result Horizontal Stress Characteristic The existence of extended shell does have influence on horizontal stress of tunnel tube. The top of H-shaped support and mid span of roof undergo more influence than other parts Horizontal Stress Result of Service Condition 18

19 Stress (MPa) X-component Stress (MPa) Analysis Result Horizontal Stress Element Joint Segment Joint Distance from Left End of Roof Slab (m) Comparison of Horizontal Stress on Element Joint and Segment Joint of Tube Mid span Support Longitudinal distance from element joint (m) Variation of Horizontal Stress along Longitudinal Axis 19

20 Analysis Result Principal Stress Characteristic The existence of extended shell does have influence on principal stress of tunnel tube. The top of H-shaped support and mid span of roof undergo more influence than other parts Principal Stress Pattern 20

21 Principal Stress (MPa) Analysis Result Principal Stress Characteristic The existence of extended shell does have influence on principal stress of tunnel tube. The top of H-shaped support and mid span of roof undergo more influence than other parts 0 Elemenr Joint Segment Joint Distance from Left End of Roof Slab (m) Comparison of Principal Stress on Element Joint and Segment Joint of Tube 21

22 Analysis Result - Displacement Vertical Displacement Pattern of Service Condition Characteristic Vertical displacement of extended shell coordinates with adjacent tube structure. Vertical displacement difference between extended end and adjacent tube structure is negligible. The existence of extended shell does have influence on displacement of tunnel tube. 22

23 Displacement (mm) Displacement (mm) Analysis Result - Displacement Element Joint Segment Joint Distance from Left End of Roof Slab (m) Longitudinal Distance from Element Joint (m) Comparison of Vertical Displacement on Element Joint and Segment Joint of Tube Variation of Vertical Displacement along Longitudinal Axis 23

24 Conclusion The extended shell at the joint is of low rigidity, but well supported by adjacent tunnel tube. Its deformation and stress are well controlled. The extended shell has limited influence on distribution of stress and deformation of the whole element. 24

25 Conclusion The existence of extended shell does have influence on stress and deformation of adjacent tunnel element, its adjacent tunnel structure bears about 10% more stress and deformation, especially on tunnel roof. 25

26 Suggestion & Prospect Consideration of the influence of extended shell on tunnel tube should be taken during design Structural performance of extended shell under interaction between elements under earthquake or settlement should be studied 26

27 Thank You 27