Report reveals Undercliff issues

By Martin Neville

Published on Wednesday, September 03, 2014 - 10:37


Report reveals Undercliff issues

Undercliff Drive following a landslip in February. Picture by Peter Boam.

IT WAS hailed as the stabilisation scheme which would finally provide a lasting solution to the highway problems in the Undercliff Drive area.

The major repair project at Undercliff Drive was only ever intended to address issues on the surface and never designed to deal with the underlying landslide on which the road sits.

However, despite Island Roads' claims it would provide a road solution that would last for years to come, a report produced a month before work started, by engineering consultants Ramboll, said it was impossible to state how long the repairs would last because of the risk of landslips.

Undercliff Drive following the February landslip.
Undercliff Drive following the February landslip.

The report, presented to Island Roads and released following a resident's Freedom of Information request, said the risk of geological failures overwhelming the proposed works was deemed very high with no mitigation measures proposed.

It added: "The proposed works do not stabilise the landslide complex.

"Movement rearward, forward and beneath the works will continue and are considered geological mechanisms; this ongoing movement will impact the proposed works."

It also stated: "The expected life of the works is dependent on geological mechanisms, primarily driven by rainfall; as a consequence it is not possible to provide a defined operational life for the works."

But in April last year, Paul Herbert, Island Roads service director had claimed the project — described by Island Roads as ground stabilisation designed to repair and maintain the road for years to come — would provide a lasting solution to the road's problems.

He said: "Undercliff Drive has seen highway movement over a long period of time and the affected areas have only received short-term repairs using available resources at the time. "The PFI investment will now provide an opportunity to develop a lasting solution to the highway problems experienced in this area."

Homes along Undercliff Drive had to be evacuated.
Homes along Undercliff Drive had to be evacuated.
The scheme — one of 18 geotechnical schemes taken on by Island Roads as part of the Island’s multi-million pound highways PFI — was brought forward last November, following increasing land movement.

It involved 'anchoring’ the highway using 25-metre steel cables driven through the clay strata into a more substantial layer of rock.

At the time, Island Roads said the solution was designed to protect the highway from movement but would not prevent the surrounding area being subject to further ground movement.

Work started in November, but before they could be completed, residents were evacuated from their homes when a giant landslip in February made it too dangerous for them to stay.

In a statement this week, the council’s head of planning, Bill Murphy, said the geological problems in the Undercliff area were well known.

He said: "At present there are no proven realistic solutions available that experts can agree would address the underlying ground conditions in the geological risk area.

"The Undercliff is the largest inhabited rotational landslip in Western Europe and over the last two centuries over 300 reported incidents of ground movement have occurred there, usually following wetter inclement weather."

He said the scheme was designed to address surface conditions at the time and pre-dated the landslip.

"The risks highlighted in the risk matrix referred to this broader geological risk, namely the potential failures downslope and upslope of the geotechnical schemes. The comments in the matrix that no mitigation was proposed reflects the fact the schemes are not designed to deal with the wider geological failure at Undercliff."

The scheme was signed off by independent experts Mott MacDonald.



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