GSHPA Workshop 16 November 2011 - Renewable Heat...Current research projects at Cambridge • Field...
Transcript of GSHPA Workshop 16 November 2011 - Renewable Heat...Current research projects at Cambridge • Field...
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Soil‐structure interactions for thermal piles/walls; Fundamentals; Design
considerations; Future research needs Kenichi Soga
Professor of Civil EngineeringDepartment of Engineering
GSHPA Workshop16 November 2011
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Acknowledgement
• Former and current researchers: Binod Amatya, Echo Ouyang, Ray Yi, Denis Garber, Yi Zhang, He Qi, Maria Canellas
• Peter Bourne‐Webb• Cementation Skanska – Peter Smith, Rab Fernie, Martin Pedley, Andrew Bell
• Geothermal International – Tony Amis, Chris Davidson• Arup – Duncan Nicholson, Anton Pillai, Paul Bailie
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Current research projects at Cambridge
• Field study on long‐term behaviour of thermal piles• A pile‐raft‐structure interaction code for thermal piles
• Thermo‐Hydro‐Mechanical finite element code for thermal piles/tunnels/walls
• Interaction modelling of building performance and GSHP (boreholes, thermal piles/tunnels/walls)
• Capacity of GSHP systems at city‐scale• Thermal response testing
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4
1200 kN1200 kN1200 kNHeat Pum pHeat Pum p
ColdHot
ColdHot
Main Pile
Heat Sink Pile
Heat Sink Pile
Main Pile
May 2007
July 2007
30m
24m
Mechanical Load Tests coupled with thermal loading
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External Loading – Building load
Internal Loading – Thermal load
Greater stress –more strains No strainNo stress
Heating Cooling
Free expansion(soft base, pile groups)
Expansion Shrinkage
End constraints(hard base, stiff structure)
Heating Cooling
Compression Tension
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Check 1: Is the stress in the concrete smaller than the strength?
Thermal stress in heating > Thermal stress in cooling. Why?
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Measurement of radial strain
Cooling
Heating
Pile Pile
A bigger diameter pile will have more radial displacement
What is the effect on heat transfer and shaft resistance?
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Check 2&3: Are the mobilised shaft friction and the end bearing pressure smaller than the design limits?
CoolingHeating
Original
But….
No change in ultimate strength?
Cyclic heating and cooling will damage the clay?
Short term test (with excess pore pressure) versus long-term performance (excess pore pressure dissipation)
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2400 kN load at the base is about 3 MPa
Laloui and Donna (2011)
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Check 4: Is the pile movement acceptable?
Laloui and Donna (2011)
Lambeth College
EPFL Lausanne
No building
Full building
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Thermal pile design software
max
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Results
M (VWSG)M (Model)M+T (VWSG)M+T (Model)T (VWSG)T (Model)
M (VWSG)M (Model)M+T (VWSG)M+T (Model)T (VWSG)T (Model)
Cooling: Es = 450 * Cu; Heating: Es = 600 * Cu
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Finite Element Analysis of Thermal Pile
Pile & Soil Pile Interface
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2.0 0 -2.0 -4.0 -6.0 -8.0 2.0 0 -2.0 -4.0 -6.0 -8.0
End of Cooling End of Heating
Stress (MPa) Stress (MPa)
Dep
th (m
)
Dep
th (m
)
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Summary for Thermal Piles• Check 1: Stress in the concrete is less than the allowable limit.
– Extreme – assume that the pile is fully restrained.
• Check 2: Mobilised shaft friction is less than the design limit.– Assume that the pile can fully expand at both ends but no movement at somewhere in the middle?
• Check 3: End bearing pressure is less than the design limit.– Extreme – assume that the pile is fully restrained. But end movement will reduce the thermally applied load.
• Check 4: Pile movement is less than what the superstructure can tolerate.– Need to do pile‐soil interaction analysis
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Thermal Walls – extracting heat from “hot” station
Wall bending?
Soil expansion – increase in earth pressure? Strut loads?
Tottenham Court Station
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Thermal Tunnels – extracting heat from ‘hot’ tunnels
Whole Model
Tunnel Segment
Pipe
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Air
Pipe
Soil
Summer
Air
Pipe
Soil
Winter
Heat extraction: 31W
Heat extraction: 47W
36 ˚C 29 ˚C
28 ˚C
17˚C16 ˚C
13 ˚C
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ArupArup
Lining stresses?
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Final remarks• Appreciation of the difference between “External” loading versus “Internally” generated thermal loading.
• We now know better, but more questions to be answered because of this.
• Opportunities and Challenges in thermal walls and thermal tunnels.
Thank you.