Jiaqi Wang

The stability of the gob-side roadway roof poses a significant challenge for safe mine production. To address this pressing issue, the gangue slurry utilization has emerged as a popular strategy to ameliorate the stress environment within gob-side roadways and bolster their structural integrity. Given the intricate nature of the internal structure of the collapse zone, this article investigates the various manifestations of key block structures within this zone, drawing insights from analogous simulation experiments. Mechanical models are established for both the key blocks and the gob-side roadway roof, meticulously analyzing the impact of the degree of slurry filling on the stability of these key blocks. Furthermore, the movement of the gob-side roadway roof is calculated, considering the shear forces exerted by the key blocks. The findings reveal that the gangue aggregate and fractured rock mass within the collapse zone collaborate to support the key blocks, effectively reducing the tangential force exerted by these blocks by more than 50%. As the filling degree of the gangue slurry gradually diminishes, the peak deflection of the basic roof gradually increases, with an average amplitude of 16.1%. These insights have been successfully applied in mine operations, demonstrating the feasibility of the gangue grouting filling method in the bottom collapse zone for controlling the surrounding rock of gob-side roadways. Specifically, when the elastic foundation coefficient of the slurry exceeds 0.11 × 10 ⁶ N/m and the width of the coal pillar exceeds 5 m, the gob-side roadway remains stable and secure. Highlights: Gangue grouting stabilizes gob-side roadways by controlling filling degree. 87% filling cuts roof stress 50% via key block stabilization. Slurry+pillar maintains 3D stress, prevents lateral peak overlap.

To solve the problem of floor water inrush in the process of coal mining on a confined aquifer and study the law of floor instability, a cemented filling mining method is proposed in the paper. Using river sand and cement as filling materials, the cementitious material with a concentration of 75% and cement content of 15% has the best flow and mechanical properties. Based on the elastic half-space theory and the bearing characteristics of the backfill, the mechanical model of floor stability is established, the critical criterion of floor instability is proposed, and the relationship between the failure depth of floor and the location and pressure of confined aquifer is obtained. The numerical simulation test scheme is designed, and the FLAC3D fluid-structure coupling element is used to explore the instability characteristics of the floor in the mining process. The research results show that the failure depth of the floor will gradually decrease with the increase of the strength of filling materials, the increase of aquifer distance, and the decrease of water pressure. The research results provide a useful reference for the study of safe mining of coal resources on a confined aquifer.

Many voids are produced in the mining process of ore-bearing strata. To explore the development law of voids after mining coal-bearing strata, a theoretical model was established to derive the overall distribution and shape of voids in the goaf. The above theory was verified using the numerical calculation method. The turning point of the void change was found. The research results show that the void in the goaf was widely distributed around the stope, and the overall void ratio was affected by the mining conditions, such as the mining height and face length. While advancing the working face, the dynamic development of the void first increased and then decreased. At first, the distribution of the void ratio in the goaf was between 0.293 and 0.889 under specific geological conditions, and then, with the advancement of the working face, a large void ratio was reserved at 0~40 m behind the working face. When the working face was advanced to the first roof collapse length, the void fractures continued to decline. Using the above voids, the backfilling of solid mine waste can be effectively realized, and the ecological environment can be protected.

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.

To resolve the problem of top mine instability and the consequent ecological damage caused by different grades of ore deposits in the layered mining process, layered filling‐pillar‐mining‐displacement method (LFPMD) is proposed using a potash mine as an example. Based on the operation principles of the tail salt filling system, the mechanical behaviours of the tail salt under initial tamping and overburden loading were obtained through compaction tests in the laboratory. In addition, the mining‐filling mass ratio of tail salt was derived. Based on the mining geological conditions of a potash mine in Laos and the compaction characteristics of tail salt, a mechanical model of top control by tail salt and a numerical model of top control by the pillars were established to discuss the stability of the upper‐layer top mine and the lower‐layer top mine. It was found that when the elastic foundation coefficient of the tail salt is greater than 550 MN·m⁻³, and the width of the retained pillars is 10 m, stability of the upper layer and the lower layer can be guaranteed. The results revealed that the LFPMD method can ensure stability of the overburden in the stope and reduce environmental damage while treating tail salt underground.

Aimed at the problem that the mining roadway is seriously affected by the repeated mining under the up-down successive cooperative mining mode, this paper takes Qiuci Coal Mine as the research background. Based on analysis of mining influence stage of A502 haulage roadway, the stress evolution and deformation law of surrounding rock of roadway are analyzed through similar simulation, the principle that the ratio of main stress affects the stability of roadway under the influence of repeated mining is obtained based on the plastic failure theory of surrounding rock of roadway, the roadway stability control method by periods and stages is put forward based on the principle of roadway stability control, and the numerical simulation scheme is designed to determine the reasonable coal pillar width and support mode of roadway. The results show that the coal pillar with the width of 8 m can reduce roof stress of roadway by 38.4% and 64.3% during the tunneling period and period after formation of roadway, and the principal stress ratio is reduced to 2; the stability of surrounding rock during and after excavation can be guaranteed by adopting φ20 × 2400 bolt and advanced hydraulic support. Through field measurement, the maximum deformation of A502 haulage roadway is only 60 mm, and the cumulative output of coal during the period of mining influence is 1,833,700 tons, thus the safe mining of coal mine is realized, and enormous economic benefits are generated.