Study On Mechanism And Risk Dynamic Prevention And Control Of Strainburst In Deep Cavern

In the context of the national "double carbon" and the deepening of the "Belt and Road" international strategic framework,the demand for major transportation infrastructure construction is growing and world-class projects are emerging.At the same time,with China’s "14th Five-Year" development plan and the vision of the 2035 proposed,more and more underground construction projects in deep buried complex geological environment.Rockburst disasters caused by high ground stress in deep are becoming more and more frequent,which has seriously threatened the construction progress and safety of deep engineering.Under the influence of complex terrain,geological conditions and high stress environment,the response characteristics and disaster-causing mechanism of multi-disaster information of rockburst will be more complicated,and prevention and control will be more difficult.Based on this,this paper systematically conducts research on the inoculation mechanism of strainburst and collaborative prevention and control technology in deep cavern by using literature research,theoretical analysis,numerical simulation and laboratory tests.The primary results are as follows:(1)Under the true triaxial condition with single face unloading,the rockburst ejection failure process can be summarized into four stages: local particle ejection,rock splitting into plates,rock plate breaking into blocks and overall block ejection.Among them,rock spalling into plates is an unavoidable failure phenomenon during the generation of strain rockbursts.The stress-strain pre-peak curve of rock samples has an obvious yield platform,and the corresponding failure phenomena are the splitting failure on the unloading face of rock samples and the shear failure within the potential rockburst pit.The mass of rockburst ejection fragments are mainly coarse grained,medium grained and fine grained fragments.The effective precursor information warning chain on the eve of hard rock strainurst is established.It is revealed that the formation mechanism of strainburst in hard rock is three progressive processes: tensile failure,shear failure and tensile-shear composite failure.(2)Under the true triaxial condition with single face unloading,the total energy conversion rate is greater than the elastic strain energy conversion rate is greater than the dissipation energy conversion rate.And the higher the elastic strain energy conversion rate,the lower the dissipative energy conversion rate,resulting in rockbursts occurring in higher intensity levels.There is an obvious energy competition evolution mechanism between elastic strain energy and dissipation energy during the energy evolution process of rockburst.That is,the elastic strain energy curve shows a sharp increase followed by a rapid release,and the dissipative energy curve shows a gentle increase followed by a linear rise.A multi-parameter criterion of rockburst energy is established,which has clear physical connotation and can coordinate physical factors,energy factors and integrity factors of surrounding rock mass.The application and verification of engineering cases show that the criterion has good validity and engineering applicability.(3)Based on the multi-parameter rockburst energy criterion,three-dimensional discrete element theory and polycrystalline modeling technology,a three-dimensional polycrystalline discrete element nonlinear dynamic-static coupling numerical analysis method is developed to accurately simulate the whole process of "inoculation-occurrencedevelopment-failure" of strainburst.The NEPER-DEM data interface calculation program and the strainburst tendency analysis program were independently developed.A3 D crystal scale fine simulation model is established.A three-dimensional failure criterion that can reflect the effect of intermediate principal stress and fully consider the tensile and shear failure modes of rock is proposed.It overcomes the limitation that the traditional numerical study of rockburst is only suitable for simulating the single failure mode of rock micro-element.The application and verification of engineering case show that the criterion and numerical method are reasonable and feasible.(4)Based on the multi-parameter rockburst energy criterion and the dynamic-static coupling three-dimensional polycrystalline discrete element nonlinear numerical analysis method,it is found that the displacement,stress,energy and rockburst tendency of surrounding rock increase with the increase of buried depth under the same lateral pressure coefficient.And the displacement,stress and energy of the vault,arch bottom and the midpoint of the two side walls are the largest.The trend of increasing displacement with the increase of burial depth is more significant.The evolution of strainburst in deep caverns can be summarized as four processes: stress adjustment,energy accumulation,crack formation and block ejection.With the core idea of reducing energy aggregation,pre-releasing and transferring energy and absorbing energy,the mechanism of deep cavern strainburst is revealed mainly based on the triggering causes,formation conditions,catastrophic processes and mechanical mechanisms of rockburst.(5)Based on the main line of "risk characteristic factors→risk dynamic assessment→risk prevention and control system",a multi-factor integrated rockburst risk assessment index system is constructed.The evaluation standard of rockburst risk assessment index is established.The superposition considers the loss severity of rockburst.A dynamic assessment method of rockburst risk level based on multi-level deep participation and multi-information integration is established.With the help of risk matrix method to determine the level of rockburst risk,the formation of a deep cavern strainburst macrocontrol strategy(strategic type)and hierarchical collaborative prevention and control technology system(tactical type).Taking Erlang Mountain Tunnel and Micang Mountain Tunnel as examples,the relevant research results of this paper are verified.