Support Parameter Design of Pre-Stressed Expandable Prop Group in Horizontal and Gently Inclined Thin-Vein Mining

A mechanics-based mathematical model is developed for the support-parameter design of a pre-stressed expandable prop group in horizontal and gently inclined thin-vein stopes. First, pressure-arch theory and equivalent-beam theory are combined to derive analytical expressions for the nonuniform roof-load distribution and roof deflection. The force method and deformation-compatibility conditions are then used to characterize the roof–support interaction and to compare the mechanical responses of retained rock pillars, conventional concrete pillars, and pre-stressed expandable props. The analysis indicates that pre-stressed expandable props establish roof contact earlier than conventional concrete pillars and require a lower reaction force than high-stiffness retained rock pillars while permitting controlled roof convergence. Subsequently, a coupled roof–prop group model is formulated using deformation-compatibility equations to determine the required support force at each prop location and to coordinate prop-group spacing with the number of steel pipes in each prop. The proposed model is applied to a field test at a gold mine in Dandong, China, and its predictions are evaluated against monitored support loads. For a 20 m stope span, the preferred center-to-center spacing is determined to be 5.0 m. The stabilized loads of the three monitored props are approximately 922, 1060, and 778 kN, compared with theoretical values of 841, 964, and 841 kN, corresponding to relative deviations of 8.8%, 9.1%, and 8.1%, respectively. All measured loads remain below the designed ultimate bearing capacities. The results demonstrate that the proposed model captures the nonuniform load-sharing characteristics of the prop-group system, particularly the higher support demand in the central part of the stope, and provides a mechanics-based basis for rational support-parameter design.