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