GPR case study: How we used GPR survey methods to investigate the construction detail and understand this unique and somewhat complex Grade II listed monument.

Background history

The Wellington Monument is a triangular tower, 24 m wide at the base and 53.34 m high, located on the highest point of the Blackdown Hills, 1.9 miles south of Wellington in the English county of Somerset. It is a grade II listed building.

The monument is built of local stone, a Calcareous Grit Sandstone. The base has an Egyptian winged panel above the studded iron door surmounted by a coved dentil cornice. A counterweight hangs inside the top of the monument to help balance it in windy weather. An internal staircase ascends to a viewing platform with three circular windows, one on each face.

The monument was designed to commemorate the Duke of Wellington’s victory at the Battle of Waterloo. Construction of the original design commenced in 1817; a revised and cheaper design was eventually used, though, and the building was completed in 1854. It is now owned by the National Trust, which closed the monument to the public in 2005 because of falling stone debris. Surveys have shown that extensive renovation work will be needed to reopen the internal staircase to the viewing platform.

GPR survey

In May 2015, Sandberg used Ground Penetrating Radar to investigate the construction details and help identify weaknesses.

Mr Ken Evans, the trust’s building surveyor, said the GPR study was one of several being carried out to “understand this unique and somewhat complex monument. The GPR seeks to identify voids and gaps in the stonework under the surface but should also tell us more about the materials used to build the obelisk.”

The survey results will also be used to build a computer model of the obelisk and help develop a “more effective repair approach.”