Phase recently had a busy weekend surveying a car park which was due to be redeveloped. Prior to carrying out an intrusive site investigation and finalising their development plans the client wanted the entire 0.8 ha site surveyed to locate sub-surface structures, trace the buried utilities and, if possible, to determine the depth to bedrock. We were given the narrow window of a single weekend when the car park would be temporarily closed during which the survey had to be carried out.
A radio frequency location (RFL) survey and a ground penetrating radar (GPR) scan were carried out to locate the buried utility apparatus. A magnetic and electromagnetic (EM) survey was undertaken to identify buried structures and metallic features. A detailed GPR survey was also carried out in several areas where the EM and magnetic surveys identified anomalies and GPR was also used, in conjunction with a low frequency antenna, to try and determine the depth to bedrock.
By combining several different techniques a range of survey objectives could be met. The entire site was covered by the EM and magnetic techniques and by analysing the data from these techniques on site we were able to target specific areas for detailed GPR survey.
The location of metallic pipes, cables and drainage routes was confirmed. The geophysical survey clearly identified several areas where in-situ structural remains were present and also a number of areas where there appeared to be concentrations of rubble. One such area may have indicated an infilled cellar or basement. The targeted GPR survey was able to provide information on the depth of these features. Several horizons were identified in the low frequency GPR data; one of which was believed to be either the top of the bedrock or the base of the made ground.