The long term stability of room and pillar workings in a gypsum mine

Abstract

The factors influencing the long term stability of mine workings at Sherburn-in-Elmet have been isolated and studied through laboratory experimentation and theoretical studies. A series of physical models were constructed and tested in order to appreciate the behaviour of the strata overlying the gypsum deposit in the event of a single or multiple gypsum roof beam failure. The effect of water on the long term stability of gypsum pillars was investigated through long term creep testing of gypsum specimens submerged in mine water. The time-dependent deformation of submerged gypsum was appraised mathematically and an empirical equation was developed for the description of creep behaviour. A procedure for the prediction of failure time of submerged gypsum specimens under a constant load was developed and graphical and computerised versions of solutions are presented. The influence of the satinspar bands on pillar degradation was investigated through servo-controlled testing of simulated pillars. A possible roof structure, a linear arch, was modelled photoelastically and the presence of tensile stresses in the structural elements was proved. Finite element modelling studies were carried out to demonstrate separately the change in the state of stress around the workings due to a roof beam failure and in the pillars due to the presence of satinspar bands.