Tower YW42 Tower Stability, Halifax

Project Summary

At Sunny Bank Farm, Southowram, Halifax, National Grid noticed that one of their suspension multiphase transmission towers was deforming and twisting on it’s base.

Soil Engineering Geoservices were contacted by National Grid’s Consulting Engineer, WSP Parsons Brinckerhoff to carry out a geotechnical ground investigation of the area around the tower to establish the root cause of the deformation.

Soil Engineering Solution

The twisted tower was located some 40m up a grassed slope with a gradient of between 30 and 40°. The area to be investigated included the area immediately around the base of the tower and therefore beneath the live overhead power lines. A solution was required that would enable provision of high quality ground investigation data, acquired safely and efficiently whilst working under the very difficult conditions posed by the steeply sloping ground and overhead power lines.

Soil Engineering Geoservices opted to use a P60 slope climbing rig capable of dynamic sampling and coring to form the 11No. boreholes at the site, each of which were formed to rock head using dynamic sampling methods and then cored to 10mbgl. 5No. boreholes were further extended to 30mbgl using open hole drilling techniques. The choice of rig had the added advantage of having a mast with a total operating height of only 4.30m which allowed working directly under the transmission lines without danger of arc-over.

Due to the slope and slippy ground conditions caused by the grass at the site, the rig and mule configuration required a system of anchoring in the form of static ground anchors.

Soil Engineering Value

By using this innovative P60 slope climbing rig capable of dynamic sampling and coring, the investigation was able to be carried out safely and efficiently without the need to resort to costly civil engineering temporary works such as scaffolding and crane lifts or multiple mobilisation of and movement of separate units of plant for overburden boring and rock coring and drilling. The use of the mule working platform also minimised the risk of manual handling of drill tooling and casings up and down the slope.

The investigation was successfully completed within the four week programme.

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