Plug technique reduces noise and prevents migration
Pennine Vibropiling's innovative use of its vibro concrete plug technique has provided an alternative design solution for ground improvement at the new B & Q Superstore being built in Kidderminster.
The site was formerly occupied by carpet manufacturers. As a result of the
weaving and dyeing factories, boiler houses and several large fuel tanks, significant
ground contamination is present.
Pennine provided the main contractor, Watkins Jones, with an alternative method
of ground improvement based on stone columns installed using its vibrocompaction
Initially, the Environment Agency objected to this proposal due to concern
relating to the possible migration of contamination down the stone columns into
the underlying sandstone acquifer which is utilised by Severn Trent Water for
the public supply. Whilst this is rarely a problem in the long term, because
of the amount of hard cover over the site when the development is complete,
during construction the situation could arise where a sudden deluge might cause
However, based on its previous experience of similar situations, Pennine was
able to satisfy the Environment Agency that the introduction of lean mix concrete
plugs at the base of the columns would prevent the possibility of any transfer
In the right geology this type of plug prevents the aquiclude – the impermeable
clay layer covering the aquifer – being pierced while still enabling Pennine’s
ground improvement technique to be used even though aquifers are present at
Quality control is extremely important when using this technique and computer
monitoring is used to ensure that the plug is in the correct position. Over
2,000 stone columns and concrete plugs have been installed to support both the
floor and main foundations.
The use of a concrete plug to overcome the possibility of migration was pioneered
by Pennine who developed the technique. It is achieved by using a specially
adapted poker which enables a small charge of concrete to be pumped at a depth
controlled by use of on-board instrumentation. Stone can then be fed down the
flot using bottom feed equipment or conventionally from the top.
There is increasing concern by the Environment Agency about potential contamination
of the aquifer as more and more brownfield sites are developed. Depending on
the specific situation, this innovative technique can often be used to provide
a solution and safeguard the environment.
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