InSAR assets in ground movements survey on abandoned coalfields

Abstract

Rising groundwater in abandoned mines may result in ground movements at the surface overlying underground works. Feedbacks on several abandoned coalfields show that ground uplift is generally observed, reaching in some cases several centimetres or more. Although such ground movements, slow and associated with slight slopes, are not expected to generate surface damages, the survey of potential ground movements on abandoned coalfield is necessary, especially to confirm the end of mining-induced subsidence. The most common used method for this mission is levelling. A retro-analysis of ground movements, based on Interferometric Synthetic Aperture Radar (InSAR) technique, covering more than 20 years after mine activity ceasing, has been realised on the French abandoned coalfield of Nord-Pas de Calais. This analysis aimed to extend ground movements detection capabilities in areas not covered by levelling as well as compare InSAR analysis to levelling data for evaluating the robustness of satellite-based displacement measurements. InSAR analysis was able to highlight ground movements of a few millimetres per year, with the same order of precision than classical levelling methods. The observed ground displacement patterns expand well beyond the coalfield, indicating the influence of non-mining-induced phenomena, such as local geology and surface morphology. Our findings underline the operational capability of space-borne InSAR for monitoring abandoned coalfields.