Wspólnotowy Serwis Informacyjny Badan i Rozwoju - CORDIS

General overview of the European situation

The significance of bacterial decay for piling constructions became obvious after 1990 in the Netherlands and in the last decade a general impression was achieved of the actual state of the Dutch foundation constructions. It became clear that within 100 years piling constructions, which were always underneath the groundwater table could be severely degraded and that some cities are more susceptible than others. Although wooden foundation constructions are well known in Sweden and Venice, the problems appear to be not so prominent in both areas. In Sweden bacterial decay in wooden piles was already recognise in 1970 but it was regarded as of minor importance for the quality of the buildings. However Venice has to deal with severe settlement problems, but bacterial degradation was not seen a possible cause of this problem.

In Great Britain and Germany wooden piling construction are of less importance, although some locations are known with buildings on wooden piles. Beside some fundamental research was carried out on archaeological wood, bacterial degradation is not an item in the archaeology, in any of the five countries. However all available information shows that bacterial degradation is the major threat to the wooden cultural heritage stored under water or in soils. As under fungal and animal activity wood is degraded fast and if the environment allows these types of degradation no wood is conserved after 100 years and no archaeological wooden remainders will be found. There are records of wooden remaining over a long period of more then 2000 years. For archaeologists the state of the wood sample is important and is related to the possibility to recognise the original sample shape and size. In wooden remains degraded by bacterial, the outline of the original sample is often intact and although it is soft its wood quality is regarded as good. It is known that after drying the wood structure will collapse and specify treatments are developed to remove the water and retain the original sizes.

Based on all experiences and fundamental research the following statements on bacterial degradation can be made:

In general
If wood is well conserved (no bacterial degradation appears) it can last for centuries and retain its strength properties;
It is believed that in combination with fungal activity, bacterial wood degradation is more aggressive;
The significance of bacterial degradation for piling constructions and archaeological wood is underestimate in Germany, Great Britain and Italy.

Related to wooden foundations:
All wooden foundation piles that have been in service for about 100 years and that are situated under the groundwater level show bacterial decay at least in their outermost layer;
The degradation process starts from the out-side and gradually decreases towards the centre of the pile;
Spruce seems to have a higher resistance against bacterial degradation than pine sapwood and alder. Pine heartwood seems to be quite resistant;
In contrast to the general trend, situations were recorded where 100 years old Spruce piles were severely degraded and in other situations 100 years old Pine piles were without any degradation;
The degree of bacterial degradation depends on the location. There are Dutch cities were the sapwood of the pine piles is fully degraded in a period of 70 years. Whereas in other cities the pine sapwood is less degraded in the same period. The degraded peal in Spruce piles is much more limited and in about 100 years this peal is less than 5mm in some cities or can be as wide as 20m in other cities.
Polluted environment with nitrogen / phosphorus seems to increase the degree of degradation and a clear relationship was found between the degree of degradation and nitrogen / phosphorus concentration in the wood;
Oxygen levels around the piles are supposed to be low;
Severe bacterial attack seems to appear more in permeable soils (such as sand), whereas the attack is less in non-permeable soils such as clay and peat;
Boron treatment is used to conserve piles but no result is available on its efficiency.

In the archaeology Pine and oak are regard as most durable species in contrast to alder, willow, beech, birch, and lime.
In contrast to the situation around piles, archaeology wood underneath the groundwater surface, degradation seems to be less fast in sandy soils than in peat or clay soils.
In archaeological wood there seems to be no relation between degree of attack and age;
With increasing excavation depth the degree of decay seems to be decreasing.
Although excavated wood seems often sound, this is not case because precautions are almost always necessary in order to avoid collapse of the wood structure and excavated wood seems to be susceptible for fungal attack.

It can be concluded that the impact of bacterial wood degradation in Europe is underestimated especially in the archaeology.

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