Research On Rockburst Characteristics,process And Mechanism Of Deep Gold Mines In The Northwest Of Shandong Peninsula

Metal mineral resources are the foundation of industrial development.In recent years,the rapid development of social productivity has consumed a large number of mineral products.Shallow surface resources are no longer sufficient to meet the demand,and underground mining of deep resources has become the mainstream.The deep ore body is under three-dimensional high stress conditions,with a complex rock mass environment.The mining process generally encounters rock burst problems,which is one of the biggest challenges to safety production in deep mines.Therefore,understanding the characteristics of rock burst occurrence in deep mines under high stress conditions and exploring the mechanism of rock burst occurrence can provide assurance for the safety production of deep mines.Relying on the national key research and development plan(2018YFC0604606),this paper takes the deep gold mine in the northwest of Shandong Peninsula,the second largest gold resource occurrence place in the world,as the engineering background,from the perspective of the occurrence law and formation mechanism of deep gold mine rockburst,adopts the method of machine learning algorithm,finite element discrete element numerical analysis and theoretical analysis to carry out the rockburst characteristics,rockburst driving force(crustal stress field),rockburst prediction Research on the process and mechanism of rock burst.The main research content of this article is as follows:(1)Revealed the rock burst characteristics of five deep hard rock gold mines in the northwest region of Shandong Peninsula,ranging from 500 m to 1100 m in depth.The types of rock failure include rock ejection,multilayer detachment,large caving,and large deformation.The characteristics of rockburst include rupture at the intersection of the roadway floor and two sides,multi-layer cracking and peeling of the roof and side walls,multiple ejection of sheet-like rock blocks from the surface of the side walls,fragmentation of rock blocks from the center of the excavation face,and large-scale ejection of large blocks of rock from the roof,mainly caused by stress control.As the burial depth increases,rock burst events become increasingly serious.(2)The size and azimuth distribution of the deep 3D crustal stress field in the northwest of Shandong Peninsula are obtained.The maximum horizontal principal stress dominates,with a direction of northwest,approximately 110 °.The ore-forming fault zone controls the deep crustal stress field of each gold mine in the northwest of Shandong Peninsula,with the strike of NNE.The direction of the maximum horizontal principal stress in the mining area is approximately orthogonal to the strike of the ore-forming fault zone.The NW compressive movement brought by the Eurasian plate and the NEE tectonic stress of the Tanlu fault zone are the external factors for the formation of the crustal stress field in the northwest of Shandong Peninsula.The results of crustal stress inversion of five gold mines show that the maximum principal stress in the same horizontal fault zone is less than the maximum principal stress of surrounding rocks on both sides,and stress concentration occurs in the footwall of the fault bend.(3)The Random Forest Model based on Bayesian Optimization(BORF)is developed for the intelligent prediction of deep rockburst in.the northwest of Shandong Peninsula.The BO-RF model achieved 100%prediction accuracy in rock burst event evaluation.Compared with the performance of the BO-RF model and seven other machine learning models in rock burst prediction,BO-RF has the best performance in both the training and evaluation datasets.The SHAP(Shapley Additive ex Planations)theory analysis shows that the greater the burial depth,tangential stress index and elastic strain energy index,the greater the possibility of strong rockburst.(4)The coupled Finite–Discrete Element Method(FDEM)was used to calculate the rock burst process caused by excavation unloading of the deep stress field in the northwest of Shandong Peninsula.It was found that the plastic damage zone occurred before macroscopic cracks,and the "V" shaped damage zone guided the "V" shaped failure after rock burst.The damage to trapezoidal tunnels,rectangular tunnels,straight wall arched tunnels,and circular tunnels becomes more severe as the burial depth increases.The degree of damage is the smallest in circular tunnels with the same burial depth,followed by straight wall arched tunnels,and the greatest in trapezoidal and rectangular tunnels.The rock burst events observed deep in the northwest of Shandong Peninsula indicate that the use of FDEM method effectively explains the unloading rock burst process of high stress hard rocks in the northwest of Shandong Peninsula.(5)The relationship between the grade of deep rockburst and the crustal stress field and burial depth in the northwest of Shandong Peninsula is established.The principal stress index rock burst criterion,principal stress difference index rock burst criterion,and maximum tangential stress index rock burst criterion have been optimized to be more suitable for rock burst evaluation in the northwest of Shandong Peninsula.In addition,the large deformation criterion of deep rock mass based on strain recovery and the energy criterion of deep rockburst based on strain energy release are proposed.The influence of excavation size and lateral pressure coefficient on strain energy release is further analyzed,the formation mechanism of deep rockburst in the northwest of Shandong Peninsula is revealed,and the support method of energy absorbing materials absorbing strain energy release is explored.