The influence of relative humidity on the rate of convergence in an underground gypsum mine

Pillars of gypsum from the underground mine located at Grozon (Jura region, France) reveal degrees of instability that vary depending on the mining period. Observations carried out with a scanning electron microscope (SEM) shed light on the dissolution of gypsum, especially on the walls of pillars and in older zones. The time-dependent behavior of the gypsum is thus investigated in the laboratory and found to be a result of forced relative humidity. Variations of relative humidity have an influence on convergence values that are measured in situ. The analysis of this data reveals seasonal developments that are a function of variations in relative humidity.