| The complex internal structure of sedimentary mesomorphic rock mass is one of the important factors causing the instability of surrounding rock mass and rock burst and other engineering disasters,and the engineering excavation effect has an important influence on the mechanical properties of rock mass around the roadway and tunnel.Therefore,it is of great significance to study the relationship between mechanical properties and energy evolution and acoustic emission parameters of anchor combined rock mass under unloading.Exampled by a certain coal mine of Zaozhuang coal and rock combination as the research object,using rock similar material made of cement mortar,through different cementation Angle to make the combination of the rock mass,then into the anchor rod and anchor standard specimens,for real excavation under triaxial unloading confining pressure test and the characteristics of acoustic emission testing,explore and anchor combination in unloading rock mass failure under the action of mechanical characteristics,The failure law is explained from the energy evolution and acoustic emission parameters to further understand the influence of bolt on the characteristics of rock mass with different contact surface dip angles.In this paper,through the research method of laboratory test,a large number of mechanical tests are carried out on the rock mass combined with anchors.The main research work is as follows:(1)Based on the test results,the strength failure law of anchor combined rock mass under loading and unloading is analyzed,and the influence of anchor bolt on mechanical parameters of combined rock mass is studied.The test results show that the mechanical properties of rock mass are greatly improved and the anchoring effect is more obvious under the condition of large dip Angle and low confining pressure.Compared with the conventional triaxial test,the rock mass with anchor is more prone to failure under the condition of triaxial confining pressure unloading,especially under the condition of higher confining pressure unloading rate.Under the influence of confining pressure,the strength of rock sample increases with the increase of initial confining pressure,and the results can be better fitted by Mohr-Coulomb criterion.The dip Angle of contact surface is also an important factor affecting the mechanical properties of rock mass.With the increase of the dip Angle of contact surface,the strength of rock mass decreases gradually,and the minimum value is obtained at 60°.According to the evolution law of stress and strain curve of unloading failure of anchored composite rock mass under different unloading confining pressure rates,the nonlinear constitutive relation of unloading failure of anchored composite rock mass is established.(2)Based on the first law of thermodynamics,the energy calculation formula is used to calculate the energy index of rock mass with anchor combination under loading and unloading conditions,and the instability failure law is explained from the perspective of energy.The results show that with the increase of confining pressure unloading rate,the energy values of the peak point of the combined rock mass with anchor decrease on the whole.The reason is that the fracture development and expansion of the rock sample are not complete and the energy consumption is less at the high unloading rate.Under the influence of confining pressure,various energy indicators show an increasing trend with the increase of initial confining pressure,and the more energy is released and consumed during instability,and the more severe damage is caused.With the increase of the contact Angle,the energy of the combined rock mass decreases as a whole,and the minimum value is at 60°.(3)Based on the acoustic emission characteristic test,analyze the evolution law of acoustic emission parameters when the rock sample is unstable and fail,and study the influence on the acoustic emission ringing count rate and amplitude under loading and unloading conditions.The results showed that with the increase of the unloading confining pressure rate,the maximum value of the ringing count rate of the anchored rock mass increases gradually,but the cumulative ringing count rate decreases,the amplitude has a tendency to increase,and the peak "lag" time shortens which rock samples are more easily damaged.With the increase of the initial confining pressure,the more energy accumulated in the rock mass,the active period of acoustic emission increases,and the accumulative ringing count rate increases gradually.Rock samples with larger contact surface inclinations are affected by the fracture mode and slide along the contact surface,producing a small amount of acoustic signal.The acoustic emission count rate will be extremely active when the rock sample is damaged,and the amplitude will increase in intensity which are used as precursors for the instability and failure of the rock mass combined with anchoring. |
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