| The development and utilization of underground space is an inevitable choice for the development of human society,economic construction and national security strategy.As a kind of non-linear,discontinuous,heterogeneous and anisotropic natural geological body,rockmass is randomly distributed with discontinuous structural planes of different scales,such as joints,fissures,weak interlayers,and faults,after a long geological process.In underground engineering,openings are usually built in the rock mass with complex discontinuous joints.The existence of joints will seriously deteriorate the integrity and bearing capacity of the surrounding rock of the openings,leading to instability and failure of the openings after being disturbed by external forces.In addition,joints will change the stress distribution mode in the surrounding rock of the openings,which will lead to different failure modes of the surrounding rock of the openings,increasing the complexity and unpredictability of the mechanical behavior of the surrounding rock of the openings.Therefore,the mechanical behavior and stability control of surrounding rock of openings in jointed rockmass have become one of the key scientific problems that are paid close attention to and urgently need to be solved in the field of rock mechanics.In this thesis,starting from the key scientific problem of stability control of surrounding rock of openings in jointed rockmass in underground engineering,based on physical simulation test method,the static mechanical properties,energy evolution and distribution law,mesoscopic mechanism of acoustic emission(AE)performance variation,and progressive instability failure process and its mechanism of granite samples with an opening,parallel jointed granite samples with an opening,and cross jointed granite samples with an opening under static loading were systematically studied combining the acoustic emission monitoring and digital image correlation methods.Meanwhile,the effects of parallel and cross joint angles on the above research objects were comparatively analyzed.On this basis,the dynamic mechanical properties,stress wave fluctuation characteristics,energy dissipation characteristics,and sudden instability failure mechanism of the granite samples with an opening,parallel jointed granite samples with an opening,and cross jointed granite samples with an opening were further investigated,and the influences of parallel and cross joint angles on the above research objects are compared and analyzed.Moreover,the mechanical response behaviors under static and dynamic loads were compared.Finally,discrete numerical simulation method was used to study the instability and failure characteristics of surrounding rock of a roadway in jointed rockmass in Sanshandao gold mine of Shandong Province under different working conditions,the instability and failure mechanism of the surrounding rock of the roadway in jointed rockmass was analyzed,and then the corresponding instability control theory and technical measures were proposed.The main research results are as follows:(1)The strength and deformation characteristics and anisotropic properties of the granite samples with an opening,parallel jointed granite samples with an opening,and cross jointed granite samples with an opening under static loading were investigated,and the variation of strength and deformation parameters of the jointed granite samples with an opening with joint angle were revealed.In addition,according to the rock energy theory,the evolution process and laws of total energy,elastic strain energy,and dissipated energy of the jointed granite samples with an opening during the deformation and failure process were studied,and the effects of parallel and cross joint angles on energy storage capacity,energy consumption,and energy distribution were analyzed.The damage and failure energy criterion of surrounding rock of underground openings in jointed rockmass was established based on the elastic energy consumption ratio,and the corresponding damage-failure energy mechanism was revealed.The results show that the three types of energy change curves of the jointed granite samples with an opening appeared "step" shape gradual mutation.The existence of joints weakened the energy storage capacity of the jointed granite samples with an opening,and the increase of the number of joints reduced the energy accumulation efficiency of the samples.The continuous mutation of elastic energy consumption ratio could be used as a criterion for crack initiation and propagation of the surrounding rock of underground openings in jointed rockmass,and the subsequent sharp mutation could be regarded as a criterion for its instability and failure.(2)The variability characteristics of AE timing parameters(i.e.,AE event rate,cumulative event number,energy rate,cumulative energy and b value)and frequency domain parameters(i.e.,AE frequency and amplitude value)of the granite samples with an opening,parallel jointed granite samples with an opening,and cross jointed granite samples with an opening during the deformation and failure process were systematically studied based on AE monitoring system,and the interrelation between the above AE parameters and the influence of parallel and cross joint angles on the evolution characteristics of those AE parameters were analyzed.AE parameters that could be used for identifying precursor information of failure of surrounding rock of underground openings in jointed rockmass were discussed,and the corresponding microscopic mechanism of AE performance variation was revealed.The results show that the evolution characteristics of different AE parameters were different,and there were precursors of surrounding rock of underground openings in jointed rockmass failure.The peak AE event rate and the most concentrated stage of AE energy release of the jointed granite samples with an opening did not necessarily occur at the stress peak point.The AE event rate decreased obviously when the jointed granite samples with an opening were damaged.The AE energy was accelerated and the critical energy release existed.The b value generally fluctuated between 0.1 and 0.9,showing a downward trend overall,and dropped rapidly before the jointed granite samples with an opening failure.The low frequency-high amplitude and the high frequency-low amplitude signals were sensitive to the changes of the stress state of the jointed granite samples with an opening and could be used as the main signal source for its failure prediction.(3)The deformation and failure process of the granite samples with an opening,parallel jointed granite samples with an opening,and cross jointed granite samples with an opening under static loading were studied combining the digital image correlation method.The evolution law of deformation field and the crack initiation,propagation and coalescence law of those samples were analyzed quantitatively and qualitatively,and the corresponding progressive failure mechanism was revealed.The results show that the local deformation concentration phenomenon was the macroscopic manifestation of microcrack initiation and propagation in the jointed granite samples with an opening,and the evolution of the local deformation concentration zone was a significant nonlinear process.The existence of joints changed the stress distribution mode in the jointed granite samples with an opening,and high stress concentration was formed at the tip of prefabricated joints and around the opening,which interacted and jointly dominated the initiation and propagation mode of new cracks.The change of parallel and cross joint angles had different effects on the crack initiation position and propagation path of the new cracks.The interaction between the tips of the same set of cross joints formed through cracks,which led to the relatively complex evolution mode of the deformation field and high damage degree of the cross jointed granite samples with an opening.The failure of the jointed granite samples with an opening was mainly caused by tensile cracks induced by the opening and joint tips,accompanied by local shear failure.Two typical types of white patches(i.e.,linear and diffuse white patches)appeared in the failure process of the jointed granite samples with an opening,and microcrack nucleation was considered as the microscopic formation mechanism of the white patches.(4)The dynamic mechanical characteristics,stress wave fluctuation characteristics,energy dissipation characteristics,and crack propagation law of the granite samples with an opening,parallel jointed granite samples with an opening,and cross jointed granite samples with an opening under different impact gas pressures were studied using Splitting Hopkinson Pressure Bar device,and the corresponding sudden failure mechanism was revealed.The results show that under the same impact gas pressure,the dynamic compressive strength and elastic modulus decreased firstly and then increased with the increase of parallel and cross joint angles,and the dynamic compressive strength increased with the increase of impact gas pressure.The dynamic compressive strength and elastic modulus were significantly greater than corresponding static compressive strength and elastic modulus.The incidented wave amplitude was positively correlated with the impact gas pressure,and the transmitted wave amplitude was smaller than the incidented wave amplitude.Under the same impact gas pressure,the transmitted wave amplitude decreased firstly and then increased with the increase of parallel and cross joint angles,and the change trend of reflected wave amplitude was approximately opposite to that of transmitted wave amplitude.The parallel and cross joint angles and impact gas pressure had significant effects on the changes of transmitted energy ratio,reflected energy ratio,and absorpted energy ratio.Under the same impact gas pressure,the transmitted energy ratio decreased firstly and then increased with the increase of parallel and cross joint angles,while reflected energy ratio and absorpted energy ratio increased firstly and then decreased with the increase of the joint angles.When the joint angle in the jointed granite samples with an opening was constant,the transmitted energy ratio and the absorpted energy ratio increased with the increase of impact gas pressure,while the reflected energy ratio decreased with the increase of impact gas pressure.Under impact load,white patches of tensile cracks presented on the jointed granite samples with an opening generally parallel to the loading direction appeared around the opening and/or near the joint tip near the transmission bar,then gradually evolved into macro tensile cracks,and finally the overall tensile failure occured.In summary,the failure modes of jointed granite samples with an opening had obvious strain rate effect and joint structure effect.(5)Taking a typical deep underground roadway of Sanshandao gold mine in Shandong Province as the engineering background,a numerical model of jointed roadway considering the actual in-situ stress state and the spatial distribution of dominant joint planes was established using 3DEC software,and the instability and failure of the surrounding rock of the roadway in jointed rockmass under impact disturbance was studied.Then,the deformation and failure characteristics of surrounding rock of a roadway in jointed rockmass under different burial depths,impact stress wave peak values,and impact stress wave delays were further studied,and the influence laws of various factors on the stability of the surrounding rock of the roadway in jointed rockmass were compared.The results show that the displacements of the two sides,the roof,and the floor of the roadway increased gradually with the increase of the action time of the impact stress wave.The damage degree of the two sides was greater than that of the roof and floor of the roadway,and the deformation damage of the two sides was more serious overall.The tensile-shear failure mainly occured in a small area adjacent to the roof and floor and the two adjacent free surfaces of the roadway,the tensile failure occured locally in this area,and the shear failure mainly occured along the joint surface outside the area.Burial depth and stress wave peak value had great influence on the dynamic stability of the surrounding rock of the roadway in jointed rockmass.With the increase of burial depth/stress wave peak value,the inward extrusion deformation of both sides,the roof subsidence and the floor heave of the roadway gradually increased,and the corresponding damage degree intensified.The effect of stress wave delay on the dynamic stability of the surrounding rock of the roadway in jointed rockmass was small,but complex.(6)Based on the results of physical simulation test and numerical calculation,the instability and failure mechanism and deformation control measures of the surrounding rock of the roadway in jointed rockmass were discussed.The instability control theory of surrounding rock of underground openings in jointed rockmass was proposed:"consolidating surrounding rock joints,improving surrounding rock strength,restoring and improving stress state,and weakening the strength of dynamic disturbance source";and then,the corresponding instability control technical measure system of "grouting reinforcement+full-face anchor(net)spray combined support+local reinforcement support+construction of impact buffer structure+reduction of engineering blasting disturbance" was constructed. |
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