Influence of relative humidity on the non-linear failure and stability of gypsum mines

A cusp catastrophic model was developed for the pillar-and-roof support system based on the simplified mechanical model of the support system and the improved stress-strain relationship for gypsum. Then, the catastrophic failure mechanism was investigated for the gypsum support system by considering the influence of relative humidity (RH). Meanwhile, the failure criterion for catastrophic instability in the gypsum support system was deduced, and the expression for the safety factor of the pillars was improved by considering the shape and size effects on the strength of gypsum. The results indicate that the RH exerts a significant influence on the catastrophic control parameters for the gypsum support system: with the increase of the RH, the catastrophic control parameters are more prone to cross the bifurcation set and meet the conditions of catastrophic instability for this system. For the input parameters used in the failure criterion, the RH mainly degrades the uniaxial compression strength and then causes catastrophic instability. According to the stability analysis for the mined-out area of the Jingmen Gypsum mines, the lower limit (about 1.60) of the value of factor relating the size effect to the uniaxial compression strength was obtained.