Stability assessment of a shallow abandoned chalk mine of Malogne (Belgium)

Abstract

The Malogne Phosphatic chalk quarry was developed by the rooms and pillars mining method within an area of 67 ha. The site is partially flooded and located in close proximity to important infrastructure as railway, highway, and residential houses. During and after its exploitation several significant ground collapses were registered. The last one, with an area of 1.2 ha and 3 m amplitude occurred in 2015 nearby the railway line. To assess the behavior of the underground openings a combination of in situ structural measurements and laboratory mechanical characterisation in dry and saturated state of the main lithology type in the quarry – white and phosphatic chalk, hard ground and calcarenites, are performed. The UCS of the chalk ranges from 4 to 10 MPa while its tensile strength is between 0.75 and 2.1 MPa. For the hardground, these values are over ten times higher. The results reveal significant influence of the water on the chalk properties by reduction of almost twice its strength. The data obtained was implemented in a conceptual geomechanical model, using the 2D FEM. Numerical results show a failure pattern that was confirmed from the in situ observations.

Keywords:

• Chalk
• shallow depth
• room-and-pillar
• stability analyses
• FEM

Acknowledgement

The authors thank the team of L’ASBL Projet Malogne for their support during the onsite work.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This research has been realized with the support of the European Fund for Regional Development in the framework of the Interreg “RISSC” project.