Water build-up blamed for Ludlow Town Walls collapse
High water pressure, possibly caused by blocked drains, may have caused the dramatic collapse of part of Ludlow's historic town walls, a leading geologist has claimed.
First, a 30ft section of the wall at Upper Linney, behind St Laurence's Church, fell to the ground and crushed a parked car in the middle of the night, then 10ft more fell as council workers were surveying the site a couple of days later
Professor Mike Rosenbaum, a geologist, has written to Shropshire Geological Society to explain his thoughts on what may have caused the collapse.
He said the use of cement rather than mortar on the wall could also have been a contributory factor – and it was unlikely that tree roots or the impact of recent minor earthquakes were responsible.
Investigations to determine the cause of the collapse are still ongoing.
In the letter, Professor Rosenbaum said: "Why did the wall collapse?
"It is still to early to explain precisely why, but such collapses are usually caused fundamentally by too high a pressure acting on the back of the wall.
"It is usually the result of high water pressure or by high earth pressure when compaction was uneven and the material settles through time dragging down the back of the wall. High water pressure can develop where drainage has not been allowed for, or the drains have become blocked.
"Aggravating causes include the use of Portland cement rather than lime mortar, which makes the wall too rigid, causes the siltstone to decay, and inhibits drainage.
"This can cause localised collapse which removes support from the surrounding wall, which then collapses.
"Tree roots and earthquakes can also add to adverse forces but their impact here is unlikely to have been great, although two minor earthquakes have indeed shaken this site in the last ten years.
"The trees in the memorial garden are rather small and set back from the wall, so their impact may well have actually been beneficial, as their roots bind together the relatively loose and weak made ground."
Professor Rosenbaum said the walls were a 'most interesting example of engineering geology'. He added: "The wall can be reconstructed and good drainage will certainly be incorporated, and possibly also buttresses to help support the new wall."
See also:
800-year-old Ludlow Town Walls collapses
Garages destroyed as Ludlow Town Walls sees second collapse
