The assessment of stress in an exploited rock mass based on the disturbance of the rigid overlying strata

Gravitational rules are used as the basis for the prognosis of vertical stress distribution in exploited rock masses. A decrease in stress in a worked-out area (decrease between the initial stress and the stress acting on the floor of the outmined seam) results in an increase in stress in the surrounding unworked area. The size of load in the floor of the worked-out area is determined by the degree of disturbance in the overlying strata rocks. An overall additional load in the surrounding rocks of the unworked area is determined based on the difference between the initial geostatic stress and the load in the floor of the worked-out area. The additional load, which is determined from the force of relieving the stress in the worked-out area divided by the periphery of the worked-out area, decreases per unit of length of the periphery of the worked-out area. Furthermore, the behaviour of stress in the direction of the worked-out area is calculated mathematically. In this way, the stress in the grid of points on the level of seams being mined can be calculated, and isolines of acting stress can be determined. As an example, we show calculations for a specific situation in a mine before rigid overlying strata failure and after the failure. After the rigid overlying strata failure, the additional stress decreased by approximately 40%.

► In this study, the stress caused by longwall mining is determined.
► Hard overburden disturbance is determined by surface subsidence monitoring.
► This disturbance provides force relief of the outmined area that is equal to the surrounding additional load.
► A mathematical formula for the stress coarse from the excavation is determined.
► Theoretical analysis is supplemented by a specific mine case.