Fluidized soil-cement mixes for backfilling of flooded cavities

This paper deals with the development of flowable soil–cement mixes to be used for filling underground cavities flooded by sulphate contaminated water. The research started from the need to backfill a former gypsum mine which was excavated with the chamber-pillar technique. The dissolution of gypsum and anhydrite, consequent to the flow of water inside the abandoned tunnels, and the possible collapse of the pillars puts at serious risk of collapse the area above the mine. The paper describes the steps which led to the definition of a cement–soil mixture characterized by rheological properties adequate to be introduced in the tunnels from the surface and substitute the sulphate contaminated water. The relationships between the composition of the flowable soil–cement mixture and its properties in the fresh and hardened state are discussed.