ROTTING TIMBER supports in British tunnels from World War I are believed to be the cause of collapsing houses in Belgium, academics revealed this week.
So far one house has collapsed and up to 50 more are threatened in the Flanders town of Nieuwpoort.
The cause is thought to be a 1.5km labyrinth of forgotten tunnels which lie under the main streets of the town. These were built in 1917 by British, French and Australian troops to escape some of the most ferocious bombardment of the Western Front.
Both handmined and cut and cover tunnels were hastily constructed in the sands, silts and clays during the third battle of Ypres, at depths of 3m-6m. The town was completely flattened, and then rebuilt on the rubble after the war without backfilling the tunnels.
'The tunnels were lined with wood and after 85 years this wood is starting to rot, ' says Professor Mike Rosenbaum of Nottingham Trent University, part of the British team which is conducting investigations. Recent fluctuations in the groundwater level have accelerated the rotting process. Wooden supports are now collapsing and the settlement is migrating to the surface.
This has prompted claims against the local water company from residents whose houses have serious subsidence cracks.
So far the full extent of the tunnels are not known, though they are being mapped from incomplete military records. This will be followed by geophysical and borehole surveys.
The results may show that other towns built on WWI fortifications in the area are in danger of collapse, said professor Peter Doyle from the University of Greenwich.