Feasibility Assessment of Cavity Detection Using Geophysical Modelling

Old mine workings and natural cavities represent potential hazards before, during and after construction on such sites, and add further complication to subsurface parameters.Geophysical techniques can be used to detect cavities but the associated subtle signals mean that site conditions must be considered when choosing techniques and survey parameters. Here we propose the use of theoretical modelling to calculate the feasibility of cavity detection using a range of geophysical techniques. Typical cavity shapes are modelled and the use of site specific parameters increases reliability. We show examples of the limitations of cavity detection as a range of associated variables are altered. Three dimensional modelling allows assessment of optimum survey parameters in the survey design stage. This approach aids discriminate choice of technique and technique survey parameters at the desk study phase of survey design. The calculation of the minimum cavity detectable at any given depth gives precise information about the limitations of any geophysical survey undertaken. This analytical and accurate technique of survey design will increase openness about the limits of particular geophysical techniques in given site conditions and also optimise a geophysical survey to any specific site.