Dans le sud de la Belgique se situent les principales sources d'eaux minérales et carbo~gazeusesde la Belgique. Leurs caractéristiques résultent de l' histoire géologique particulière de cette région.

A case history illustrating an innovative application of borehole radar tomography to foundation problems in a karstic area is presented. The principles of the method and the geotechnical interpretation of the results are discussed. It is shown that, although ground conditions may be considered as very unfavourable for reflection radar techniques, good results were achieved in the crosshole mode, giving valuable information on both the geometry and the characteristics of the subsurface.

In Wallonia, spoil heaps are an important element of the landscape and of the patrimony. They are sometimes worked for recovering the residual coal or as filling material. The spoil heaps instabilities occur mainly during their construction and the causes and mechanisms are well known. A less frequent instability type comes from the spontaneous combustion of the residual coal which induces some heterogeneity in the spoil heap mass and lead sometimes to instantaneous and more or less important slides. After a short recall of the spontaneous combustion phenomenon, the paper presents three recent case histories of unstable burning spoil heaps. The geological, hydrogeological and geotechnical surveys performed and. in case of need, the stability studies and the proposed solutions.

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