Network Rail – Installation of GSHP Test Loop

Project Summary

In January 2010 Soil Engineering were appointed by Network Rail to carry out a structural and geotechnical investigation at London Bridge Station. The works were in anticipation of the redevelopment of the station as part of the Thameslink Programme. As works progressed over a two year period Soil Engineering were requested to undertake additional works at the station.

Phases One, Two and Three of three works comprised an array of investigation techniques to ascertain the engineering properties of the ground and underlying strata and the constituent make-up of the existing structures of the station and five bridge structures associated with the station lines. Phase Four, instructed in February 2012, comprised an archaeological survey and the formation of a deep borehole to install a geothermal loop.

Soil Engineering Solution

The geothermal loop borehole was formed within one of the arches located beneath London Bridge Station. The limited headroom within the arch required the mobilisation of a specialist low headroom rotary drilling rig. The rig was set up within a bunded area and the walls and roof of the arch covered with protective sheeting to guard against drilling arisings. The borehole was commenced using 10” diameter tools and casing to 10m below ground level. Aquifer protection was installed to prevent downward migration and cross contamination within the Chalk Aquifer. The borehole was competed using Geobore “S” drilling techniques to a depth of 150m below ground level.

A 40mm diameter, 150m long loop was installed into the borehole with centralising spacers and the annulus backfilled with a specially designed thermal grout. The borehole and loop design was specified by Consulting Engineer WSP Environment and Energy. A Thermal Conductivity Test was carried out over a 48 hour period.

Value

The results of the Thermal Conductivity Test will be used to design the Ground Sourced Heat Pump well field to meet the anticipated heating and cooling requirements of the new London Bridge Station. The bulk of the works have been undertaken using in house labour and resources and this has aided achievement of a defect, incident free phase of works.

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