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Landslide - Blaina, South Wales
Ward Jackson Associates have investigated and monitored the moving hillside above Westside, Blaina, in Gwent from the winter of 1991 to the present day. At the request of the local authority, Blaenau Gwent County Borough Council, WJA looked into and costed a number of alternatives for stabilising the one million tonne landslide and in early 2001, prepared a detailed design and tender documents for a major earthworks and drainage solution (value circa £3m) to stabilise landslide.
Work
commenced on site in September 2001 and continued through the unusually
dry winter of 2001-2002. Halting the movement was successfully achieved
by the end of that winter by the construction of a series of deep drains
to intercept major groundwater flows. Earthworks to reshape the landslide
and reduce the out of balance forces were completed during summer 2002.
Close behind the earthworks was the installation of an extensive system
of
rock-filled counterfort drains and horizontally-bored groundwater relief
drains. Further work to peripheral areas of the hillside and completion
of the excess earthworks disposal site on the industrial estate on the
far side of the A467 Brynmawr to Newport trunk road, was completed during
the summer of 2003.
In
his 1927 paper to the South Wales Institute of Engineers, Professor Knox
recorded that failure of parts of the Inkerman Tip had taken
place in Blaina, demolishing in the process a row of houses half way up
the slope, known as Alma Row. Inkerman Tip was a colliery spoil tip that
sat on the northern half of the current landslide. Over the following
70 years, the Ordnance Survey maps
show
that other properties in Westside, just to the south, had been similarly
lost due to landslide. In recent winters,
running up to the winter of 2001-2002, periods of wet weather brought
accelerating rates of ground movement reaching in excess of 3 metres per
month. Following completion of the stabilisation works, precise monitoring
of the main landslip to June 2008 detected no significant movement.
WJA
also acts as Planning Supervisor for the project, administering the health
and safety requirements of the Construction (Design and Management) Regulations
1994.
WJA
have helped Clients deal with a number of difficult instability problems
since the Practice was set up in 1991.
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