Car parking at the Gibside Estate

THE PROBLEM

Unexpected low strength ground conditions discovered on site presented the project team with the potential for additional excavation and delayed construction which would result in increased costs. Even gaining access to the area was proving difficult as CBR values less than 0.5% were encountered across the site.

THE SOLUTION

A Tensar MSL incorporating layers of Tensar TriAx geogrid was installed to allow safe and stable access onto the soft ground with further assessment made to provide a stabilised foundation to the final car park construction.

PROJECT DESCRIPTION

Work had commenced on constructing an additional car park at the National Trusts’ picturesque Gibside Estate on the outskirts of Newcastle-upon-Tyne when site operations had uncovered areas of existing formation soil with significantly lower strength soils than had been anticipated. Formation CBR values as low as 0.4% were measured in the exposed soils.

Following the discovery of these extreme ground conditions, Tensar International was approached by the project team to provide proposals to enable construction to continue and avoid unnecessary delay.

Tensar’s engineers proposed a Tensar MSL to provide safe and stable access over extremely soft soil conditions and ultimately to provide a stabilised foundation for the car park when construction had been completed. A locally sourced recycled granular fill was used along with layers of Tensar TriAx geogrid to stabilise the granular layers.

The Tensar proposal reduced the amount of additional excavation into the soft soils as well as minimising the amount of imported stone required in the construction phase. As a result, a cost saving of around 10% was achieved compared to that for the original construction depths envisaged.