To solve the problems of surface deformation and destruction of buildings caused by urban mining and realise the coordinated development of mining cities, the solid backfilling method was used to extract coal resources beneath the buildings of Tangshan. Based on surface deformation monitoring data of the continuously operating reference station (CORS) system for the past 5 years, the surface deformation process caused by solid backfilling was analysed. The final results revealed a maximum surface subsidence of 66 mm in the T zone coal area and 31 mm in the F zone area. Furthermore, the surface control effects of the caving method and the solid backfilling method were compared and analysed, and it was shown that solid backfilling could meet the surface building setup requirements. Moreover, based on the probability integral method, the effects on surface deformation due to the surface length of the F zone, compression ratio, and coal pillar width were analysed, and the effects on the prediction results due to the subsidence factor, tangent of the major effective angle, and offset distance of the inflection point were studied. The results showed that the compression ratio is the main factor controlling the surface deformation and that it should be kept above 80% for solid backfilling of urban mines. The subsidence factor should be 0.82, and the tangent of the major effective angle should be 2.15 when the surface subsidence of solid backfilling is to be predicted. This paper provides a technical reference for the realisation of urban mining with solid backfilling.

With the gradual increase in mining depth of coal resource exploitation, deep backfilling mining has effectively solved the impact of strong deep mine pressure and strong mining disturbances. However, after deep backfilling mining, the backfilling material is subjected to high stress for a long time, and its viscoelasticity has a significant impact on the roof control effect. This paper uses a large-scale bulk confinement test device to analyze the viscoelastic properties of gangue, establishes a high-precision fractional viscoelastic creep model, and identifies the gangue parameters. The established fractional viscoelastic model was used as the foundation model of the beam, and the roof model based on the fractional viscoelastic foundation was solved. The top deformation characteristics of elastic foundation and fractional foundation were compared and analyzed, and the time effect, viscoelastic effect, and order effect of the fractional order viscoelastic foundation beam were discussed. The results show that the viscosity of gangue increased under the action of deep high stress. As time increased, the roof deformation also increased. In order to more effectively control the long-term deformation of the roof, the viscosity coefficient of the backfilling material should be greater than 20 MPa. This research provides relevant guidance for the requirements of backfilling materials for deep backfilling mining and the prediction of long-term dynamic deformation of the roof in underground excavations.

When a coal mining district enters its final mining stage, the coal resources in boundary areas usually present irregular shapes, and the width of section coal pillars varies with the working-face dimension. Therefore, the stability of section coal pillars under unequal-length working faces is critical for roadway maintenance and working-face mine-pressure control. At present, most international studies on remnant-coal-pillar mining focus on regular-shaped section pillars and mainly concentrate on mine-pressure control, while few investigations concern the high-efficiency mining design for remnant coal pillars. Taking an irregular occurrence area in a Xinjiang mining area as the engineering background, this paper analyzes the geological and mining conditions from the perspective of working-face mining design and establishes a collaborative roof-control model for unequal-length working faces. The distribution law of main roof load under unequal-length working faces is revealed. It is identified that the coal pillar adjacent to the room-and-pillar goaf is the key object for roof mine-pressure prevention and control. A discriminant formula between the ultimate strength and height–width ratio of unequal-width coal pillars is derived. Combined with the load distribution characteristics of the stope, the theoretical reserved width for unequal-width section coal pillars is proposed. Field practice shows that the actual pillar width in situ is basically consistent with the theoretical calculation result. During mining, the maximum dynamic pressure coefficient of the working face is only 1.12, and the maximum roadway surrounding-rock deformation is less than 300 mm, which realizes effective stope mine-pressure control.