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

Abstract

In 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 behaviors of chalk. A hydromechanical model is also under development to analyze 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 details the observatory, its objectives and perspectives, as well as the first results after two years of activity.

Experimental investigation on the hydromechanical behaviour of a porous chalk

“…It was observed that the saturated sample (under zero suction) and low confinement had a low resistance which shows the high sensitivity of this chalk to water saturation degree. In the Royer mine, the state of the pillars is stable even with a very high saturation degree (around 95%) [2]. Those better characteristics are related to the quasi-saturated state under suction in which the pillars are, due to surface evaporation.…”

“…There are a few numbers of previous experimental results available on this chalk [2][3][4][5][6][7][8] so the new results obtained in this work will complete and compare with the previous ones to give a more extensive database.…”

“…The degree of saturation going from 90% at the surface of the pillar to 98% towards the core as indicated by [2], the surface area created by the desaturation of the chalk probably ensures a confinement that allows it to be maintained thanks to the suction generated. A total resaturation without confinement of the sample would lead to its collapse [10].…”

“…Due to the seasonal environmental changes (water table, hygrometry) the pillars of mines in chalk are often submitted to variations of the degree of water saturation. These changes could affect the short-and long-term stability of pillars in the underground quarries [2].…”

Influence of geology and topography on the occurrence of mine massive collapse—back-analysis of a historical collapse of chalk mine (France)

“…From a hydrogeological perspective, the two main aquifers are the Loing alluvial aquifer and the regional chalk aquifer which join together at the edge of the valley, perpendicular to the old Beaulieu mine. Near the site, the chalk water table currently fluctuates between 67 and 73 m asl (Conil et al, 2023), while the alluvial water table, close to the level of the Loing, is around 65-67 m asl. Wells which were present inside the Beaulieu mine, attest that the water table was located at a depth of around 2 m during exploitation of the mine.…”