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ROCK AND SOIL

SLOPE ENGINEERING

The developer on a residential project needed to solve the problem of what to do with a mudstone and sandstone rock face that would sit beside new homes on a site in the north of England.

A soil confinement product, new to the UK, has been used on an excavated rock face at the boundary of a development in Sheffield.

Ground investigation work on the brownfi eld site - the former home of a 19 th century steelworks -revealed a stable rock face made up of mudstone and sandstone.

Once the development is complete, some of the homes will stand close to the slope so contractor Thomas Ben needed a solution that would be acceptable to the future residents of the properties.

The company carried out the groundworks and decided to use PRS Geoweb's soil confinement solution following consultation with client Barratt Homes and design engineers Abatech International.

The contractor's director, Paul Mellins, says: 'The main aim for us was to provide a walling solution that would reduce erosion impact and be aesthetically acceptable, particularly as the wall would only be 1.2m from the houses at several pinch points along its length.'

'Traditional walling products such as crib-walling in timber or concrete and gabion walling were discounted, as the end result in such close proximity to a residential dwelling would have looked overwhelming, ' says Mellins.

Geoweb is a cellular confinement system made from high density polyethylene (HDPE). It was originally developed by the US Army to solve the problem of moving vehicles over soft terrain and was used to build access roads in the desert during the Gulf War. The material is generally used for slope stabilisation, earth retention and for providing load support, particularly in areas where soil conditions are poor.

A series of lengths of Geoweb cells were used at the Penistone development. Temporary frames helped with the installation by holding the cells apart until they were infi ed with topsoil. The frames were used again for subsequent layers. After installation, and over time, the cells will be vegetated.

In addition, much of the rock face to be concealed and stabilised consisted of a jagged excavated slope. Using Geoweb meant that it was able to successfully accommodate the many rough edges found along the surface.

Excavators were used to install the cladding. The structure is 6m high and 275m in length and provides a profi ed vegetated facing, using the Geoweb as cladding. This face butts up to the existing stable slope, consisting of clays overlying rock, which is excavated prior to installation. The fi nished slope is located along a site boundary and is visible from many of the properties.

'The large expanse of rock face that existed at the site would have been both unsightly and imposing. Once planting takes place in the spring it will look like a natural vegetated feature while also being a stable structure, ' claims PRS UK regional manager, Kiran Mistry.

'Contractor Thomas Ben was assigned to the project and approached us to deliver a solution that would work for them; be acceptable to client Barratt Homes and also acceptable to the end client, the house purchaser, ' says Mistry.

The rock face project was completed last December, within the specifi ed timeframe of eight weeks.

It came in at a cost of about £80,000, including installation.

'The end result is an appealing structure of a significant size for the future residents of the development, ' says Mistry. 'The soil confi ement solution demonstrates both its fl exibility and how well it can be applied on this project.'

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