Application of ground penetrating radar for locating buried impediments to geotechnical exploration and piling

Geotechnical exploration in strata containing boulders pose problems leading to wear and tear of equipment and time and cost over-runs due to the inability to foresee their presence. In addition, piling through such strata, particularly on hill slopes, is also a vexing problem, especially in the case of large diameter piles, which are commonly used for high-rise buildings. In locations, where buildings had already existed and are now demolished for redevelopment, there could also be buried impediments like old foundations or active utilities and other objects. Ground penetrating radar (GPR) could help in locating the buried objects and obstructions to drilling, excavation, and piling. The study described here deals with the instance of a site, admeasuring 21 m by 30 m, of a demolished building where a high-rise is being planned. Owing to unavailability of plans of the forty-year old building, which was demolished, GPR scanning has been used successfully to locate several of the buried footings and some boulders. The available antennae had central frequencies of 80 and 200 MHz. It was possible to get adequate information through these for carrying out exploration and preliminary selection of the locations of the pile foundations for the new building. Apart from visual interpretation of the radargram, digital classification using support vector machines (SVM) has been carried out. The inputs for the classification have been derived through the application of Hilbert transform to the signal amplitudes after post-processing of the radar data.