Filling of a flooded gypsum mine with a flowable soil-cement mix

This paper describes the use of a fluidized soil-cement mix to fill a former gypsum-anhydrite mine located in the village of Santa Brigida in Northen Italy. The mine was excavated with the chamber-pillar method on four different levels and it was abandoned several tens of years ago. Two lower levels are flooded and the dissolution of gypsum and anhydrite, consequent to the flow of water inside the tunnels, puts under serious hydro-geological risk the area above the mine. Geological and geotechnical studies found as the most adequate solution to the problem the complete filling of the tunnels with a material with mechanical and physical properties comparable to common properties of soils. Nevertheless, the presence of water with significant concentration of sulfate ions inside the tunnels has required a specific study in order to define both an appropriate filling material and the technology to introduce it in the tunnels. The results of laboratory studies to develop and characterize the flowable soil-cement are summarized and a pilot work is described.