The prehistoric pile dwellings in upper Lake Zurich, Switzerland originated 4000 years ago and were awarded the status of a UNESCO World Heritage Site in 2011. These unique sites provide essential insight into Alpine European communities the in the Neolithic and Bronze Age. The pile dwellings around Lake Zurich represent 10% of all known sites of this nature through Europe. When natural erosion and shipping-related turbulence endangered these unique structures in the shallow water zone, geotextile filter and protection sand mats were brought in to secure the pile dwellings for posterity.
GEOSYNTHETIC SAND MATS ON LAKE ZURICH
Prehistoric buildings are an irreplaceable source for research work. At Lake Zurich, it became clear that only if we are successful in protecting these sites in the long term will future researchers also have a chance of using new technologies to shed greater light on the history of mankind.
The archaeologists of the Canton of St. Gallen were therefore looking for ways to secure the pile dwellings over an area of 1,400m². They needed a long-term solution that would not damage delicate objects in the lake mud.
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After numerous investigations and loading tests were conducted, SYTEC Bausysteme AG provided the solution: Terrafix® sand mats from NAUE. This geocomposite material, with its geotextile components and a sand ballast layer, could be easily placed directly from a roll over the areas to be protected. It could then be covered with 20cm of gravel in a safe manner that would preserve the underlying historical objects.
HOW THE SAND MATS WORK
Terrafix® is a fibre-reinforced, polypropylene sand mat which is mechanically bonded over its entire surface area. The sand is entrapped between two nonwoven geotextiles and held firmly in place by the fibres.
The high specific weight of the encapsulated sand layer helps efficiently sink the large panels, enabling a fast, finely controlled installation process under water while ensuring high positional stability. Additionally, the Terrafix® sand mat has excellent filter characteristics. This geocomposite was originally developed to prevent the underwater erosion of slopes and of river, lake, and sea beds. The geocomposite was engineered for performance in turbulent flow conditions.
PILE DWELLINGS PRESERVED
The sensitive project adopted the solution proposed by SYTEC and site works progressed as planned. The geosynthetic approach to preserving these essential sites for European history proved to be a highly effective long-term solution and one that was provided economically. It was not a typical project for geosynthetics, but it further showed the ease of adaptability and suitability of these materials throughout infrastructure.
For more information on the use of these sand mats in infrastructure, visit www.naue.com.
Location: Pile dwellings at Rapperswil-Jona
Client: Archaeology Section of the Canton of St. Gallen
Project Management: HSR University of Applied Sciences, Rapperswil Competence centre for plastics in construction KIB
Contractor: Kibag Bauleistungen AG
Geosynthetic(s): Terrafix®sand mats from NAUE