Stress evolution in floor strata beneath remnant coal pillars and mechanical response of roadway surrounding rock

To address the limitations of fully characterizing floor stress distributions under disturbance induced by remnant coal pillars using a single stress indicator, this study systematically investigated the stress evolution in floor strata beneath coal pillars and the mechanical response of the roadway surrounding rock through theoretical analysis, numerical simulation, and field monitoring. A load-bearing stress distribution function for coal pillars was derived based on the Mohr–Coulomb yield criterion, and a stress superposition model for multiple coal pillars was established. The stress concentration coefficient, stress gradient, and lateral pressure coefficient were introduced to quantitatively characterize the floor stress distribution in terms of stress level, spatial gradient, and stress state. The results showed that ① floor stress was markedly nonuniform under disturbance induced by remnant coal pillars. The stress disturbance was intense in shallow floor strata and decayed rapidly and nonlinearly with increasing depth. The stress disturbance induced by the coal pillars was mainly concentrated within a depth range of 20–30 m. ② The stress concentration coefficient, stress gradient, and lateral pressure coefficient all had marked regulating effects on the peak stress and peak displacement of roadway surrounding rock. As the stress concentration coefficient increased, the peak stress increased approximately linearly, while the peak displacement increased at an accelerating rate. As the stress gradient increased, the peak stress increased linearly, while the rate of increase in peak displacement also increased. When the lateral pressure coefficient exceeded 1.0, the peak stress and peak displacement increased rapidly and nonlinearly. High values of both the stress gradient and lateral pressure coefficient markedly intensified stress concentration and deformation in the roadway surrounding rock. The peak displacement was more sensitive to parameter changes than the peak stress.