Presented by Liu Kejin
Research team: Chu Jian, Liu Kejin, Li Mangyuan, Guo Wei,
Wu Shifan, Yan Jun
Centre for Infrastructure Systems, NTU
Feb 08, 2012
Use of suction caissons for foundations for underwater infrastructure and underwater city of the future
Outline
• Suction caisson
• Feasibility
• Advantages of suction caisson
• Challenges of suction caisson
• Lab investigation
Outline
• Suction caisson
• Feasibility
• Advantages of suction caisson
• Challenges of suction caisson
• Lab investigation
Suction caisson
A typical caisson in site
and its half profile (Maniar, 2004)
Outline
• Suction caisson
• Feasibility
• Advantages of suction caisson
• Challenges of suction caisson
• Lab investigation
Part of the City of New Orleans is below sea level and is protected by levees
(after Andersen et al. 2007)
Feasibility
A underwater city in Bulgaria. Diameter = 459 m and depth = 22 m
http://www.techeblog.com/index.php/tech-gadget/underwater-city)
A underwater Hotel in Japan
http://images2.sina.com/english/life/p/2009/0108/U137P200T1D210354F12DT2
0090108194534.jpg
Troll A Condeep platform
http://www.hrc-
usa.com/images/projects/Trolls.jpg
Snorre tension leg platform(North Sea 1991)
(Andersen 2007)
http://www.freepatentsonline.com/6685396-0-large.jpg
http://www.offshore-technology.com
Deep water anchoring system
http://cdn.venturebeat.com/wp-
content/uploads/2009/10/wind-turbine.jpg
Offshore Wind Power Structure
Offshore Concrete oil tank
Outline
• Suction caisson
• Feasibility
• Advantages of suction caisson
• Challenges of suction caisson
• Lab investigation
• No ground treatment is required;
• Settlement is very small and developing very slowly;
• As it relies on shaft friction, it resists both compressive and tensile load which is important for underwater structure;
• Relatively easy and reliable to estimate the bearing capacity of the foundation;
Advantages of suction caisson
Outline
• Suction caisson
• Feasibility
• Advantages of suction caisson
• Challenges of suction caisson
• Lab investigation
• Soil plug during installation
Challenges of suction caisson
Seabed
Suction
• Soil plug during installation
Challenges of suction caisson
Soil surface
Suction
• Soil plug during installation
Challenges of suction caisson
Seabed
Suction
• Soil plug during installation
Challenges of suction caisson
Seabed
Suction
• Soil plug during installation
Challenges of suction caisson
Seabed
Suction
Ideal condition Actual condition
• Soil plug failure: Much more soil is
running into the caisson compartment
and further penetration is impossible.
Challenges of suction caisson
Seabed
Soil flow
Δu
Challenges of suction caisson
seabed
Soil flow
Keep the underpressure less than the
allowable underpressure
• Soil plug heave makes the final penetration depth of the suction caisson less than the target depth.
• Soil plug failure keeps suction caisson from further penetration thus cause installation failure.
Challenges of suction caisson
Outline
• Suction caisson
• Feasibility
• Advantages of suction caisson
• Challenges of suction caisson
• Lab investigation
Research Studies
• Model tests: Different types of soil and different caisson designs are/will be tested and loaded to failure to develop the suction caisson method, study the soil-caisson interaction and failure mechanisms, and provide data for the development and verification of the theoretical predictions and numerical models.
• Analytical and numerical tools: Based on the improved understanding through the model and pilot tests, theoretical and numerical models will be developed for the design of suction caisson and for foundation analysis.
Laboratory model tests Small scale model: (finished)
Intermediate scale model: (in progress)
Large scale model: (incoming)
Caisson(Unit: mm) Tank(Unit: mm) Soil Test type
Diameter Length Wall thickness Diameter Length
Small 70 250 7 300 500
Clay Installation;
vertical load Intermediate 205 400 25 1000 1000
Large 1000 2000 100 4500 4500
Andersen,
Jostad et al.
2008(NGI)
557 320 8* 1600 850 Sand Installation
Zhu, Kong et
al. 2010 1000 500 5* 5000 6000 Sand
Horizontal
load
Laboratory research on suction caissons
Intermediate scale test
Laboratory model tests
Small scale test
300mm
1000mm
Large scale test
Laboratory model tests
Small scale test
Intermediate scale test
Property Kaolin
Specific Gravity 2.61
Liquid Limit, LL (%) 61
Plastic Limit, PL (%) 38
Initial Water Content, w ~80%
After consolidation, w ~43%
• Vane shear test:
• Su=9.9kPa~16.6kPa
• Sensitivity: 1.69~1.81
1. Soil Sample
2. Model caisson
Highlight:
(1)Made of concrete
and steel
(2) Fully instrumented
(3) A piston: monitor
soil plug
Diameter: 205 mm;
Length: 400 mm;
Wall thickness: 22.5 mm;
Self weight: 255N(25.5kg)
2. Model caisson
Measure soil plug
Soil surface
Suction
Soil surface
Suction
Measure soil plug
Soil surface
Suction
Measure soil plug
Soil surface
Measure soil plug
Step 1 Consolidate kaolin
Step 2 Take off plates. Put caisson on the surface of kaolin. Apply suction.
Intermediate scale test
Model caissons
Thank you