| With the depletion of shallow mineral resources,China has gradually entered the deep mining stage.The frequency and intensity of spalling,rockburst,large deformation and other disasters are significantly increased than those in shallow mines,which have become problems that must be solved in the construction of deep underground engineering.The deep engineering disasters are caused by the mechanical properties of rock itself,the complex geological environment and the dynamic response of excavation disturbance.The increase of depth leads to the increase of in-situ stress,so spalling,rockburst and large deformation caused by high in-situ stress are the key factors for restricting the design and construction of deep shaft.The mechanical characteristics and engineering response of deep rock under high in-situ stress are obviously different from that of shallow rock,which leads to the frequent and sudden underground engineering disasters.Therefore,it is of great significance to study the stability of surrounding rock under high in-situ stress.This paper is supported by the national key research and development program-the key technology for shaft construction and lifting of deep metal mine.Aiming at the scientific problem of stability analysis and control of surrounding rock in shaft excavation of deep metal mine,this paper takes deep shaft excavation in Shaling Gold Mine as the engineering background.Based on the in-situ stress distribution characteristics,mechanical experiments of rock in different depth,numerical simulation and theoretical analysis,the variation law of rock mechanical properties,energy evolution and engineering response characteristics with depth is studied.At the same time,combined with acoustic emission monitoring technology,the disaster mechanism of hard brittle rock under high in-situ stress is analyzed,and the corresponding control measures are proposed.The related research results provide theoretical support for the stability analysis of surrounding rock and excavation support in deep shaft construction.The main research results are as follows:(1)On the basis of stratum integrity in shaft construction area of Shaling Gold Mine,the variation law of in-situ stress field in 560-1532m range is obtained by means of hydro fracturing in-situ stress measurement in main shaft,auxiliary shaft and return air shaft.The direction of maximum horizontal principal stress between engineering construction area and coastal area in Shandong Province was revealed.The formation mechanism of the maximum horizontal principal stress direction is explained from the perspective of plate motion,and the complex geological environment of rock in different depth is clarified.(2)Taking metagabbro and granite as the main research objects,the types,mineral composition and microstructure of rock matrix were detected by X-ray diffraction(XRD)and binocular transmission and reflection polarizing microscope;Then,the rock mechanics experiments under static and dynamic loading are carried out,and the variation of rock mechanical behavior and brittle failure characteristics with depth is analyzed from the mechanical characteristics,failure modes,acoustic emission signals and instability failure evolution process.At the same time,the micro morphology of fracture surface was obtained by scanning electron microscope(SEM),and the brittle failure mechanism of hard rock was elaborated.Finally,based on the multi-criterias rockburst criterion,the impact proneness of deep rock is evaluated,and the impact risk and impact potential are used to characterize the possibility and strength of rock impact failure in deep strata.(3)Rock energy storage capacity is an important index for energy criterion of rock burst disaster.Based on the theory of ultimate energy storage,the variation law of rock energy storage capacity with depth is studied.The influence of confining pressure on progressive failure of rock is revealed by studying the variation of characteristic stress and energy in two stages.Through the triaxial cyclic loading and unloading experiments,the evolution law of mechanical parameters in the loading process is analyzed,and double effects of strengthening and damage on rock strength parameters under cyclic loading and unloading are revealed.The evolution law of mechanical parameters also indirectly reflects the relationship between rock energy storage and dissipation.On the basis of above research results,a modified CWFS(cohesion weakening and friction strengthening)model is proposed;Meanwhile,the evolution and distribution law of total energy density,elastic strain energy density and dissipated energy density in the process of rock failure under loading and unloading are systematically analyzed.The energy evolution law that the accumulation of elastic strain energy is predominant and dissipation energy is the auxiliary before peak stress is further revealed.At the same time,the energy evolution and distribution law have significant confining pressure effect;Finally,the relationship between damage and stress level is analyzed from the angle of energy dissipation.Based on the development law of dissipative energy,the failure energy criterion of surrounding rock is established,and the damage energy mechanism of deep surrounding rock is revealed.(4)Based on the theory that the energy dissipation is mainly used for the generation of cracks and mutual friction in the failure process of brittle materials such as rocks,dynamic mechanical experiments of deep granite under different impact velocities are carried out by Separate Hopkinson Pressure Bar(SHPB).The relationship between dynamic compressive strength and impact velocity of deep rock is obtained.The relationship between dynamic compressive strength,fracture morphology and impact velocity were obtained,and the results of static loading tests were compared and analyzed.The evolution law of dissipation energy density,transmission energy density,incident energy density with impact velocity were analyzed.The fractal dimension characteristics of fractured rock samples after impact failure were revealed,and the internal mechanism of sudden instability failure of surrounding rock in deep stratum was explained.(5)Combined with acoustic emission(AE)monitoring technology,the relationship between AE signals and stress level in the loading instability process of deep rock is systematically studied by using characteristic parameters(count rate,energy rate,cumulative count,cumulative energy)and wave(amplitude and peak frequency).The stability of rock under different stress levels is calculated,and the AE precursor characteristics for predicting rock failure are put forward,so as to provide theoretical basis for AE field application.Through cyclic loading and unloading experiments,the irreversible characteristics of rock are analyzed.The change characteristics and rules of AE signals in different stress and deformation stages are obtained,and the nonlinear aggravating process of rock damage is revealed.Finally,evolution law of AE b value during loading/unloading is obtained,which provide theoretical basis for further inversion of rock damage and failure mechanism.(6)The wave velocity,rock quality,water,in-situ stress distribution characteristics and laboratory rock mechanics experiments were considered comprehensively,and the Hoek-Brown strength criterion is used to reasonably obtain the rock mass mechanical parameters in different depth.The variation law of stress field,deformation field and plastic yield zone with depth in main shaft is analyzed systematically by numerical simulation software(FLAC3D),and the space-time evolution law and characteristics of surrounding rock mechanical response are summarized.The relationship between the damage range and the failure degree of surrounding rock and depth is analyzed by damage approach index,and the range of the minimum support depth and the safety support depth are determined;Based on the energy accumulation characteristics of surrounding rock after deep shaft excavation,the energy accumulation range of surrounding rock is determined,the occurrence position and strength of surrounding rock spalling and rock burst are reasonably predicted,and the corresponding support measures are also proposed.The main shaft strata of Shaling Gold Mine are divided into different dangerous areas according to various factors affecting the stability of surrounding rock.The relevant research results can provide theoretical basis for risk analysis and control of deep shaft construction in metal mines. |
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