Research On Controlling Deformation And Instability Of Slopes Induced By The Movement Of Overlying Strata In Underground Mining Of Coal Underlying Slopes

Open-pit mining,due to geological conditions,technology,safety,and stripping ratios,often results in a significant amount of slope retained coal.The slope retained coal becomes permanently lost as internal disposal and reclamation processes conclude,leading to substantial waste.This issue is widespread in various regions of China,including Inner Mongolia,Xinjiang,Shaanxi,Shanxi,and Yunnan.To minimize the waste of slope coal resources,underground mining methods are increasingly utilized.However,the stability of the slopes surrounding these underground mines is a major concern.These slopes typically exhibit deformation,damage,and instability under the disturbance of underground mining,posing significant safety hazards and limiting efficient resource recovery.Therefore,understanding the mechanisms of slope instability and slippage caused by underground mining of the slope coal,as well as developing effective control measures,is a critical issue facing the fields of geotechnical and mining engineering.Addressing this challenge is not only of theoretical significance but also holds practical value in ensuring the stability of slopes affected by mining activities.In light of the aforementioned issues,this paper takes the geological occurrence and production technical conditions of an open pit in Pingshuo Mining area as the background,adopts a comprehensive approach.This approach includes indoor mechanical experiments,physical and numerical simulations,mechanical analysis,on-site industrial measurements,and applications.The focus is on the deformation,damage,and instability slippage of slopes affected by mining activities.Through this research,the research has identified patterns and characteristics of overlying rock movement,slope deformation,damage,and instability slippage under the conditions of edge coal underground mining.It also reveals the mechanisms by which the movement of overlying strata induces slope instability and slippage,identifying the primary causes of slope instability and slippage under underground mining conditions.Based on these findings,the study has developed a system for controlling the stability of slopes affected by mining activities.By implementing control methods to manage the severity of deformation and damage to the slopes,the research has established a stable control system for slopes during slope coal underground mining.This system ensures slope stability while achieving high-yield and efficient recovery of slope coal.The research concludes with a series of principal conclusions and innovative results:(1)Mechanical and acoustic emission tests have been carried out on major rock formation media,revealing the relationship between their mechanical behavior and the evolution of acoustic emissions,as well as the characteristics of their ruptures.This research has yielded mechanical parameters for the main rock layer media and detailed information on their macroscopic and microscopic rupture characteristics and types of damage.These findings provide data support and a scientific basis for conducting similar physical and numerical simulation experiments.(2)Starting from the sudden nature of slope deformation and damage,along with the complexity,discontinuity,and zonation of the damage modes,a physical model of the miningaffected slope was constructed.The evolution law,formation mechanism and the coupling failure relationship between the "horizontal three-zone" and "vertical two-belt" of mining slope in side coal mining are revealed.The moving mode of mining slope along longitudinal settlement and sliding and transverse horizontal sliding,as well as the characteristics of the primary and periodic movement stages of "vertical two-belt" are expounded.Findings show that the initial movement leads to the formation of a collapse zone,while periodic movement results in a fracture zone.In conjunction with the evolution patterns of acoustic emissions,the research identifies a coexistence of step collapse and tensile and shear fractures as characteristic damage features of miningaffected slopes.(3)A numerical model for dual-coal layer mining in slope coal underground mines was established.This model analyzes the patterns of instability and slippage of mining-affected slopes under various underground mining disturbances.It reveals the dynamic evolutionary mechanism of slope instability and slippage under underground mining conditions and identifies the key issues that make downslope mining more favorable than upslope mining.The study finds that mining the coal layer beneath the overlying goaf area can lead to the formation of "arc-shaped" slip surfaces,shear slip zones,and localized instability and slippage in the mining-affected slope.A critical factor in the preference for downslope over upslope mining is the difference in the collapse angles at the cutting eye and the end of the working face.(4)A "masonry beam" mechanical model was established,the dynamic evolution law of "masonry beam" of mining slope and the relationship between the rotation mechanism of key rock block B and the instability slip of mining slope are revealed.It was found that the main reasons for the instability and slippage of the mining-affected slope are the repeated movement of the "masonry beam" structure,the continuous forward progression of the "horizontal threezone" structure,and the rotational instability of key rock block B,which generates a horizontal thrust force.(5)A mechanical model was developed for calculating the depth of horizontal sliding in the slopes affected by slope coal underground mining.This model derives formulas for calculating the depth h and length L of the sliding surface under conditions of near-horizontal and inclined(dip and counter-dip)rock layers.Based on the actual conditions of the rock layers in the mine,calculations were performed for the sliding depth h and the length of the sliding surface L.The results obtained from theoretical calculations were found to be consistent with those from simulation experiments,it provides a theoretical basis for determining the depth and length of sliding instability of mining slope in Pingshuo Mining area.(6)Through simulation experiments and mechanical analysis,the study reveals the relationship between the stage-by-stage damage characteristics of mining-affected slopes and their instability and slippage.It was found that the "superficial transformation" and "structural transformation" stages are key phases causing deterioration in slope stability and leading to deformation and instability.The sliding mechanism of "goaf cave-bedding creep-slope instability" of mining slope in side coal mining is put forward,and the control methods of "partial filling in counter-dip mining" and "backfill toe pressuring" for controlling the key rock B of "masonry beam" are put forward.A comparative analysis of these methods showed that both can effectively control the stability of mining-affected slopes,but "backfill toe pressuring" is superior to "partial filling in counter-dip mining".Based on these findings,engineering applications and validations were conducted,providing a guarantee for high-yield and efficient recovery of slope coal.