Study On Forming Mechanism And Anchorage Character Of Zonal Disintegration In Rock Mass Of Deep Tunnel Under High Geostress

In recent years, with the rapid and stable development of the national economy, the utilization and developing of the underground cavern have been getting to deep embedded area. In the condition of complex geological environment such as high geo-stress, high osmotic pressure, high temperature and excavation induced disturbance, there appears special engineering response character, such as the large deformation, great rheology, etc. Among which the zonal disintegration phenomena is the most attractive problem. Specialists both home and abroad carried on much research on this, but there isn't a uniform conclusion on the forming mechanism yet.Under the financial support of National Natural Science Foundation of China (Grant No.40772173) and taking the deep tunnel which the embedded depth is 910m in Dingji coal mine of Huainan mine area as the background, the in-situ monitoring method, the true triaxial geomechanical model test, theoretical analysis and numerical simulation method are jointed together to research the forming mechanism and anchorage characteristic under high geostress entirely. Take the theoretical analysis and engineering practice tight coupling, the work in some aspect have been finished and listed below:1) Through the in-situ monitoring, the zonal disintegration phenomena is proved to be existed, and the displacement law of wave crest and trough distributed alternately during the forming procedure which is different the shallow embedded tunnel is got. The results showed that the fracture shape of zonal disintegration are related to the radius of the excavated tunnel.2) through the model test of the axial compression on the cavern obligated, it is found that the axial high geo-stress is the important factor which lead to the zonal disintegration.3) The zonal disintegration phenomenon is first reappeared in laboratory through the geomechanical model test. And the displacement and radical strain changing law of wave crest and trough distributed alternately during the forming procedure which is different the shallow embedded tunnel is got. The fracture shape and displacement distribution law is accord with the in-situ observations.4) The self-developed high geo-stress true 3D loading model test system can be used to apply triaxial high stress synchronization and independently.5)the crack propagation trajectory in surrounding rocks are got based on research. First, the computing method of crack extension under compression is established, and then takes it into the computing of crack extension trajectory through the XFEM. The numerical result shows that the crack will intend to form the circle fracture when the crack propagates to some length.6) Through the research on the stress field and energy field of deep tunnel surrounding rocks, the forming mechanism of zonal disintegration was established, there exists the discontinuity of strain and crest value of tangential stress and energy aggregation in the elasto-plastic zone, which make the crack propagation and forming circle fracture. After the formation of the circle fracture, the surrounding rock mass will unloading, which make new stress redistribution and the new plastic zone's forming. The process list up will repeat in the new plastic boundary and induce the forming of the zonal disintegration phenomena. The reason of changing laws of alternation of crest and wave displacement and radical strain in surrounding rocks was revealed, which is the constant formation of newly plastic zone make the strain and displacement break in the newly formed plastic zones.7) Through the research, it is found that the geo-stress character of zonal disintegration forming is that the axial geo-stress is the first or second principal stress, and the fractured zones formed one by one. When the geo-stress is not enough to the criterion, the zonal disintegration formation will stop. The fractured shape of zonal disintegration is related to the radius of excavated cavern and mechanical parameters of surrounding rocks, and the radius of all fractured zones are equal ratio, which explains the phenomenon observed in test and in-situ monitoring.8) The initiation criterion of zonal disintegration is established. Fist, the sliding crack model in polar coordinates system is established, and when propagate to some length it is equivalent to the circle crack. The stress intensity factor is computed through the complex variables functions, and the zonal disintegration start to form when it is larger than the fracture toughness.9) The forming criteria of zonal disintegration are established based on the energy balance theory:first, the strain energy released through excavation and unloading is regarded as the energy resources of surrounding rocks damage, and the releasable strain energy was computed. Then, Take it to compare with the energy dissipatation during the formation of the circle fracture, the energy criteria of zonal disintegration is got.10) Make the zonal disintegration initiation criteria programmed and implant it into XFEM platform of Abaqus, the zonal disintegration phenomena is simulated. The fracture shape and fracture zones of zonal disintegration got from simulation are fit with the zonal disintegration phenomenon observed in test.11) Through the geomechanical model test of anchorage character of deep tunnel rock mass, the suppress impact of anchor on the zonal disintegration was found. The compression-tension alternation phenomena in rock bolt is got, which reflects that there exists the trend of forming zonal disintegration in deep rock mass.12) through the research on the energy of the anchorage can absorbed when it is entirely yield, the criteria of suppress the zonal disintegration based on the energy balance theory is got. The rock bolts arrange pattern to suppress the zonal disintegration phenomenon is researched preliminary.