SYNOPSIS:

The present paper deals with climate change impact on stability of underground cavities due to its indirect effect on ground water levels. In France, several back-analyses have confirmed that variations of underground water tables play a key role in the genesis of surface disorders above shallow mine workings. The paper presents the forecast impacts of climate change on the behaviour of underground water tables as well as the consequences of those variations on the stability of disused underground cavities. A particular collapse that affected the Paris Basin during a major flood of the Seine River, one century ago (January 1910), with dramatic consequences, illustrates the importance of water variation impacts on the rock mass behaviour. The high sensitivity of the extracted material (very pure chalk) to water as well as the dynamics of the mine flooding process are described. The most realistic mechanisms and scenario enabling to explain massive failure of the underground workings are then discussed.

1. INTRODUCTION

The existence of a global warming process of the global climate is now well admitted by the scientific community. The rise of the average temperatures of air and oceans, as well as the observation of the de-icing of ice caps and the rise of mean sea level constitute some clear indicators. The various studied prospective scenarios, depending on the efficiency of prevention policies engaged by governments show that, up to 2100, the average rise in temperature on the surface of the Earth could vary between 1,5 and 6 °C [1]. Such a temperature increase would be likely to generate serious disturbances on climatic parameters (e.g. modification of rainfalls, disturbances of water tables). Numerous international studies are being performed in order to make progress in the understanding and prediction of the consequences of the presumed climate change. Among these studies, very few relate to the matter of underground cavities. The paper deals with the impact of climate change on stability of underground cavities. This topic may become a serious problem in France due to the existence of very numerous (hundred of thousands) shallow underground cavities, natural or manmade, well known or totally unlocated, undermining French territory. Several recent examples have confirmed that, among those, the level and variations of underground water tables have a key role in the genesis of surface disturbances. Major trends concerning the forecast impacts of climate change on underground water tables as well as the consequences of those variations on the mechanical behaviour of shallow underground workings (impacts on strata and discontinuities) are thus briefly presented. Among others, the specific case of a ground collapse (with dramatic human consequences: 7 deaths and 7 severe injured persons) that affected the Paris Basin during a major flood of the Seine River, one century ago is then described, as a perfect illustration of the importance of water variation impacts on rock mass behaviour. The chalk mine of Lorroy (city of Chateau-Landon), collapsed in January 1910, in direct connection with the flood of the Seine River.

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