GPR case study: How we used GPR survey methods to investigate and survey Platforms 1-8 and the concourse area of Paddington Station.

Survey objectives

The investigation aimed to undertake a train station platform survey and concourse area investigation to identify areas of voiding, variations in construction detail, general features and anomalies. This information enabled others to undertake a strength assessment of the surveyed areas.

Survey method

GPR was used for the survey because it could provide the required information non-intrusively, and the survey could be conducted at night when the station was closed, therefore causing no disruption to the public.

The different penetration depths and resolutions required and the large area to be scanned made this survey ideal for a multi-channel GPR survey. By using a custom-built multichannel system based on the GSSI SIR-30, we were able to scan with multiple antennas, including different frequencies (an array of two 900 MHz and two 400 MHz antennas was used), to collect all the required GPR data with a single pass. The area was scanned on a 0.5 m orthogonal grid to provide detailed coverage.

Survey findings

The construction of the platforms and concourse varied considerably. Large areas of the platforms and concourse are constructed of precast planks (from the GPR data, we were able to identify twelve different types of precast planks). The construction was mass or reinforced concrete or vaulted arch construction where precast units were not found.

Numerous other features, such as possible voids, layer interfaces, linear features (possible services), column foundations and anomalies, were also detected and reported.

Results were presented in CAD drawings showing the location and extent of the different construction types and other detected features.