Caractérisation hydromécanique et modélisation du comportement de la craie de Chateau-Landon (77)

International audienceCet article présente les résultats d’essais obtenus sur des échantillonssaturés visant à une caractérisation du comportement hydromécanique de la craie deChâteau-Landon (77). Un modèle de comportement élastoplastique de ladite craie, inspiréde la micromécanique est en cours de développement. Les premières simulationsassociées aux résultats expérimentaux vont permettre d’enrichir sa formulation

Hydromechanical characterization of Château-Landon chalk behavior

International audienceThe paper deals with the effect of water saturation degree on the stress–strain responseof a high-porosity and pure chalk, the Chateau-Landon chalk. A general experimental methodologyis presented, including hydrostatic and triaxial compression tests performed under drained conditionswith loading paths combining variations of stresses and water saturation degree to characterize thehydromechanical behavior of this porous material

Experimental investigation on the hydromechanical behaviour of a porous chalk

This paper deals with the impact of climate change on stability of abandoned subsurface cavities in chalk due to its indirect effect on ground water levels. It is the first part of a general work on the hydromechanical behaviour of a partially saturated soft rock (a porous chalk) and the effect of changes in water saturation degree. An experimental investigation including a laboratory-testing program is presented. Different degrees of saturation are imposed by controlled relative humidity conditions. Conventional hydrostatic and triaxial compression tests are performed under drained conditions for saturation degree up to 100% under low confining pressures. The obtained results have allowed to show up fundamental aspects of the chalk behaviour. The high sensitivity of the extracted material to water is described and a water induced plastic deformation is observed

Experimental Investigation of Saturation Effect on the Mechanical Behaviour of Château-Landon Chalk

International audienceAbandoned underground mines appear to be very sensitive to the variations in their environment. Due to seasonal environmental changes often related to climate and resulting in changes in the water table and hygrometry, the pillars are often subjected to cyclic variations of saturation. This could affect the short- and long-term stability of these abandoned structures. In this paper, a preliminary study on the behaviour of Château-Landon chalk has been carried out. Samples were extracted from pillars of the abandoned Royer chalk mine (Château-Landon, France). The mechanical behaviour of this chalk was then investigated by performing conventional hydrostatic, triaxial compression, and creep tests under drained conditions at different water saturation degrees and confining pressures. The obtained results show up fundamental aspects of this chalk behaviour. Its high sensitivity to water and confining pressure are described, and a water saturation-induced plastic deformation is analysed. The results presented in this paper provide some key mechanisms that can be used in the framework of back analysis and expertise in underground chalk mines, as well as the data required for the development of a specific constitutive model

An underground research laboratory at Château-Landon (France) to study the impact of climate change on the stability of abandoned mines

International audienceIn January 1910, a chalk mine at Château-Landon in the Paris basin brutally collapsed, causing 7 fatalities. This dramatic event was related to the centennial flood of the Seine River and one of its tributaries, the Loing River, which invaded the lower parts of the mine and eventually weakened the entire structure. To understand the conditions that triggered the disaster and anticipate other catastrophic event of this kind elsewhere, the Royer mine, located in the same area, was chosen to host an underground scientific observatory. Its goal is to study water–rock interactions and in particular water circulation and unusual ground saturation conditions on the behaviour of chalk. The Royer chalk mine is shallow, above the water-table, easily accessible and globally stable. It has been equipped with a high resolution multiparameter monitoring network in 2019; all the sensors are connected to The French National Monitoring Centre for Ground and Underground risks (Cenaris). Besides from in situ observations and monitoring, series of laboratory tests are carried out on samples to study the impact of hydraulic cycles on the short- and long-term behaviours of chalk. A hydromechanical model is also under development to analyse the results and better assess the overall stability of the mine in the context of climate of change. In this paper, we provide a brief summary on the challenges to assess geohazards from abandoned chalk mines, and then present in detail the observatory, its objectives and perspectives, as well as the first results after two years of activity