Preservation orders for Perco

Perco's trenchless approach to sewer installation made sure there was no damage to property or protected trees in recent works near the village of Darley Dale, in Derbyshire.

The project took place at St Elphin's Park, an historic house, which later became a Victorian spa and then a boarding school.

Baggaley Construction, based in Mansfield, is converting the property into an Audley retirement village of 126 homes.

Although invisible on the surface, trenchless technology played an important part in preserving the site's architectural and environmental heritage.

Perco was called in because a groundworks team could not risk excavation to upsize a sewer serving the building.

The mature, deciduous trees in the 44-acre grounds are a fully protected part of the site and any damage to their root systems had to be avoided.

The trenchless engineers were able to solve the problem, using two separate techniques, over short but crucial distances.

Negotiating the building foundations, Perco dug a 1.5m-square pit inside the building and drove out a 10m, timber-built heading to connect with a new 2m-diameter shaft in the grounds.

New sewer pipes were then installed and the heading back-filled using structural foam.

The 2m shaft, also installed by Perco, provided the launch point for a guided auger bore to an existing manhole.

The auger encountered some very old, unrecorded foundations but succeeded in installing 55m of Naylor Denlock clayware drainage pipes at 225mm diameter.

A blank end on the pipe kept the new pipe clear until the main contractor could complete the sewer connection at a later date.

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