Sandberg used GPR survey methods to investigate Platforms 1-8 and the concourse area of Paddington Station.
The purpose of the investigation was to identify areas of voiding, variations in construction detail, general features and anomalies. This information was to enable others to undertake a strength assessment of the surveyed areas.
The different penetration depths and resolution required, as well as 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 2 900MHz and 2 400MHz antennas was used), to collect all the required GPR data with a single pass. The area was scanned on a 0.5m orthogonal grid.
The construction of the platforms and concourse varied considerably. Large areas of platform and concourse are constructed of precast planks (we were able to identify twelve different types of precast planks). Where precast units were not found, the construction is mass or reinforced concrete or vaulted arch construction.
Numerous other features such as possible voids, layer interfaces, linear features (possible services), column foundations and anomalies were detected.
Results were presented on CAD drawings showing the location and extent of the different construction types and other detected features.