GeoCorner

Author: Jaakko Sainio

Supervisor: Sanandam Bordoloi

Advisor(s): Matias Napari, Ramboll Finland Oy

Funding: City of Helsinki 

Abstract: 
The utilization of timber piles has decreased over the years. The shift towards
materials such as concrete and steel is justified by their strength properties and
wood’s susceptibility to biological degradation. In addition to the typical load-bearing
foundation application, timber piles were previously utilized in ground improvement
applications such as slope stabilization and embankment piling. Timber pile-specific
suggestions in Finnish design guidelines are limited to essential requirements and
restrictions on their use as a load-bearing foundation. However, there are no such
restrictions for ground improvement applications, which provide greater freedom for
innovation and design.

One cubic meter of wood will store approximately one ton of carbon dioxide.
Installing timber piles permanently below the groundwater table seizes the decaying
process and stores the carbon for hundreds of years. The ecological advantages have
sparked interest in reviving the ground improvement applications of timber piles.
With correct design and suitable conditions, timber piles can provide a technically,
economically, and ecologically functional alternative to the most common ground
improvement methods. This thesis aims to support the utilization of timber piles in
ground improvement applications by examining the advantages, disadvantages, and
potential of different methods.

The thesis was conducted through a literature review, by assessing design methods
and possibilities, as well as case reviews of three constructed projects and two design
projects by the City of Helsinki. The results indicate that embankment and slope piling
are both promising methods. Both end-bearing and cohesion piles can provide a stable
foundation for embankments. Slope piling projects are yet to be conducted, although
the method is promising, and the availability of computational methods increases the
attractiveness of the solution. Additionally, studies have shown that timber piles not
only enhance soil conditions in friction soils by compaction, but also improve soil
properties in the surrounding cohesive soils.