Guide för grundläggning av vindkraftverk i kallt klimat Study ... - Tyréns

Ex-jobbsbeskrivning
Anders Helander 0243-21 33 84 2010-04-08
Svensk titel
Guide för grundläggning av vindkraftverk i kallt klimat
Engelsk titel
Study of Wind Turbine Foundations in Cold climates
På uppdrag av det engelska vindkraftsbolaget RES och det svenska
dotterbolaget NV Nordisk Vindkraft ska Tyréns AB sammanställa en ”Guide för
grundläggning av vindkraftverk i kallt klimat” där delar av ”guiden”
är avsatt för att skrivas av en examensarbetare. Arbetet skall skrivas på
engelska.
Bakground
A number of foundation solutions are possible to support wind turbine foundations,
including reinforced concrete gravity bases, rock anchored concrete or steel bases and
piled reinforced concrete caps. The type of foundation appropriate to a particular
location is determined by the depth to competent bearing material, as well as other
factors such as concrete availability and delivery logistics. To date, NV has constructed
only reinforced concrete gravity base foundations in Sweden.
Where it is located at sufficiently shallow depth, gravity base foundations are founded
on sound bedrock at a depth of 2 to 3m below ground. If bedrock is found slightly
deeper, the foundation can be over-excavated and brought back to the required level
using compacted stone structural fill. This does not normally cause concern with
respect to ground frost penetration cold climates.
Where bedrock is relatively deep, it is often overlain by glacial till which can be a
suitable material in which to found the gravity base foundation, subject to adequate
bearing capacity and stiffness parameters. However, the presence of shallow
groundwater (or other source of water), combined with a silty till may lead to problems
of frost heave, thaw settlement or loss of strength during freezing and thawing events
associated with cold climate conditions. The specific loading conditions imposed by
wind turbines, such as cyclic loading may lead to particularly sensitive foundation
behaviour. In northern areas of Europe, including Sweden, foundations must be
designed to protect them against the risk of such frost action.
Scope of work
• Review available literature relating to design and construction of foundations in cold
climates
-The initial review shall document the available publically available
information from journal and conference papers, codes and standards
and existing design guidelines. Significant work has been undertaken in
Scandinavia, North America, Russia and Japan relating to the design and
construction of transport and oil & gas infrastructure in Arctic regions, as
well as more fundamental research which should be reviewed and
referenced as appropriate.
Beställare: Tyréns AB
Study of Wind Turbine Foundations in Cold Climates
c:\documents and settings\pil\local settings\temporary internet files\olk15e\exjobbsbeskrivning (nv).doc
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Ex-jobbsbeskrivning
Anders Helander 0243-21 33 84 2010-04-08
-A general discussion on the principles of soil and concrete response to
freezing and thawing events and the risks on wind turbine foundations
shall be provided as background, based on relevant extracts of the initial
review.
• Generate a map of ground temperature and ground frost penetration for Northern
Europe using available information from literature and/or design codes;
• Discuss and if possible quantify the effects of soil type, presence of groundwater,
snow cover, altitude, vegetation etc on frost penetration;
• Summarise the effect of frost penetration on foundation capacity and geotechnical
behaviour – frost heave, thaw settlement, liquefaction, effect of cyclic loading etc;
• Summarise the effect of frost action on reinforced concrete exposed to air or soil,
including core damage and scaling/spalling due to repeated freeze/thaw cycles;
• Document the frost susceptibility of different soil types and define suitable tests to
determine potentially problematic soil conditions;
-The susceptibility of soils to the action of frost penetration is significant to
the definition of risks to the foundations. Methods of assessing the
susceptibility of various soil types shall be documented, including
appropriate testing methodologies that are accepted and used in practice
in Scandinavia and elsewhere.
• Discussion of methods to address the effect of frost penetration into the ground;
Objectives of the study
1) To summarise the issues related to the construction of foundations in cold climates
and freezing ground;
2) To document the sensitive soil types and conditions in which ground frost needs to
be considered, along with methods used to evaluate soil properties;
3) To evaluate and identify potential methods of design and construction to address
the effect of freezing ground;
Beställare: Tyréns AB
Study of Wind Turbine Foundations in Cold Climates
c:\documents and settings\pil\local settings\temporary internet files\olk15e\exjobbsbeskrivning (nv).doc
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