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Drilled pile technology in retaining wall construction and energy transfer
Application de la technologie des pieux forés à la construction des murs de soutènement et au
tranfert d´énergie
Lehtonen J.
D.Sc.(Tech.), Turku University of Applied Sciences, Finland
ABSTRACT: The use of steel piles has grown substantially in the Nordic countries during the last few decades. The growth has been
supported by active research and development contributing a versatile collection of pile types and applications. Open section drilling
is an example of new micropile inventions. Drilled pile walls and energy transfer applications extend the use of drilled piles to sites
where conventional piling has previously not been seen as an option and where the drilled piles can be seen as hybrid structures
functioning partly as vertically loaded piles, partly as lateral capacity of the retaining wall, or a heating/cooling distribution system.
RÉSUMÉ : L'utilisation des pieux en acier a connu une forte croissance dans les pays nordiques au cours des dernières décennies.
Cette croissance a été soutenue par beaucoup de recherche et de développement en contribuant une collection variée de types de pieux
et d'applications. Le forage à section ouverte est un exemple de nouvelles inventions des micropieux. Les parois de pieux forés et les
applications pour le transfert d'énergie étendent l’utilisation des pieux forés à des sites où les pieux conventionnel n'ont pas été
considérés auparavant et où les pieux forés peuvent être vus comme des structures hybrides qui fonctionnent en partie comme des
pieux chargés verticalement, et en partie comme la capacité latérale du mur de soutènement ou comme une installation pour la
distribution de chaleur /refroidissement.
KEYWORDS: steel pile, micropile, open section drilling, energy pile, drilled pile wall.
1 INTRODUCTION
Development of drilled micropiles and versatile micropile
applications have been subjects of extensive international
cooperation since the 1990s. As a regular meeting, the
International Workshop on Micropiles IWM has been held
eleven times from 1997 until 2012. Since 2006, the IWM has
been organised by the International Society for Micropiles (ISM
2013).
In Northern Europe, micropiles are commonly end bearing,
in diameter 75…300 mm, drilled or impact driven, sometimes
jacked, screwed or vibrated piles (Lehtonen 2011). Use of
micropiles has grown significantly since 1980s; in Sweden, for
instance, from 150.000 m/a (1991) to 687.000 m/a (2011) when
the total market varied from 1.620.000 m (1991) to 2.200.000
(2001) (Swedish Commission on Pile Reseach 2012).
Micropiles are in common use mainly for following purposes:
(i) Underpinning.
Hundreds of houses - detached or multi-storey houses - have
been underpinned in Scandinavia by impact driven, steel
micropiles. The main reason for underpinning is decay of
existing wooden piles, which were an acceptable ground
engineering method for houses up 1970s. Typical applications
are driven or drilled piles of type RR115 (114,3x6,3) or RD140
(139,7x10) giving a service load about 300…1000 kN.
(ii) Light load on soft soil.
Typical load under a structural wall of detached or semi-
detached houses is 20…30 kN/m giving a service load to a pile
about 100…200 kN. A common application is a slender driven
steel pile, as type RR90 (88,9x6,3) or RR115 (114,3x6,3).
(iii) Industrial construction.
There are a great number of manufacturing buildings in
Scandinavia locating on very soft soils. Additional construction
– between existing buildings and production machinery – is
Figure 1. Drilled pile wall.
continued typically with driven micropiles of type RR140 or
drilled RD170 (168,3x10), a service load respectively about
500…1400 kN.
The latest innovations in steel pile technology cover mainly
drilling. There are several new methods for concentric and
eccentric drilling developed in Finland since 1990s. Drilled
piles have been used for new applications contributing hybrid
techniques where the steel pile can be a part of a drilled
retaining wall (Fig. 1) or energy transfer distribution system.
2 OPEN SECTION DRILLING
Traditionally, the drilled piles have been made of hollow steel
sections and the drilling methods are often originally developed
for oil or water well drilling. Drilled piles are embedded using
either top hammer or down-the-hole (DTH) techniques. Drilled
piles can be grouted or non-grouted; grouting can be done
simultaneously during embedding or after drilling, using gravity
of pressured grouting.
