Study on the bearing characteristics of random lumpiness gangue from a gob roof

The final publication is available at Springer via http://dx.doi.org/10.1007/s10064-022-02927-1.The bearing characteristics of random lumpiness gangue formed by rock fragmentation in gob roofs are important to ensure roadway stability in the new nonpillar mining approach. In this paper, the bearing characteristics of gangue are divided into bulking and compaction characteristics. Bulking characteristics mainly depend on the lumpiness and bulking coefficient of randomly lumpy gangue (KRAFT). This paper proposes a method to invert KRAFT of gangue samples with a small amount of lumpiness, and a random subset of 30% of an experimental sample of broken rocks is selected for analysis. The lumpiness distributions of the subset of samples and all the samples are normal, and the average lumpiness error of the subset is 0.54–2.86%. The ratio of average lumpiness to rock before breakage (KASB) is introduced as a parameter for analysis. The results show that KASB and KRAFT have a log-normal functional relationship, and KASB can be used to infer KRAFT from laboratory and field monitoring data. Compaction characteristics show that the relationship between KRAFT and the supporting force of gangue (sGB) is a power function, and sGB in gangue during different stages of compression in a gob can be obtained from the value of KRAFT obtained from experiments or field monitoring.This work is supported by the Open-end Research Fund of State Key Laboratory for Geomechanics and Deep Underground Engineering (SKLGDUEK2024), the National Key R&D Program (No. 2016YFC0600900), the National Natural Science Foundation of China (No. 52074295, 52074299, 41941018, 52074300), the Excellent Youth Fund of the Education Department of Hunan Province (21B0487) and China Scholarship Council (CSC NO. 202006430081), which are gratefully acknowledged.Peer ReviewedPostprint (author's final draft

Discrete Element Simulation Analysis of the Bending and Toppling Failure Mechanisms of High Rock Slopes

The high rock slope situated in the Southwest stope of Taiping Mining, Inner Mongolia, is subject to dumping failure due to its instability. The dumping body rock layer of this stope shows obvious bending and lowering of the head. The overturning angle of the rock strata can reach 46°, and tension dislocation along the rock joint can be observed in exposed sections and at the bedding and lithologic interface. The sliding surface also displays a broken line morphology. Through evaluation of regional rock integrity parameters and rock soft and hard parameters, rock-mass strength based on Hoek Brown strength estimation criteria can be developed. Based on the discrete element method, the geological model of layered excavation of the thin layer slope can be constructed. Combined with indoor and outdoor assessments, the characteristics of toppling deformation of the thin layer open-air slope can be studied and summarized. In this study, simulation analysis showed that under first excavation conditions, a crack-, dump-, and antislip zone was formed. The rock in the crack zone formed a “<”-shaped fracture along the slope surface that was squeezed towards the bottom of the slope. In the lower dumping area, the deflection angle gradually increased with excavation, and the deformation range and levels in the antislip area increased with excavation. Following the third excavation, the antisliding zone disappeared and the toppling line changed from a broken line to a straight line. In the final state, the slope collapsed as a whole, with the collapse of the dumping body penetrating the top to the foot of the slope