The Formation And Evolution Mechanism Of Excavation Damaged Zone Under Deep Tunnel Excavation

The formation and evolution of excavation damaged zone (EDZ) under deep buried tunnel of surrounding rock has been the complex scientific problems of the rock mechanics, experimental mechanics, damage mechanics, fracture mechanics and structural geology and other multi-disciplinary cross each other. With the further development of rock engineering constantly, geological disasters, to conduct deep buried under high stress, much attention has been paid to the breeding mechanism of geological disasters and geological disasters with the excavation process of tunnel, especially the characteristics of microscopic and macro damaged evolution for the deep rock mass under the condition of excavation unloading, the comprehensive in-situ test method of the excavation damaged, zone, the influence of excavation depth, the size of the tunnel, the excavation way rate to excavation damage zone formation and evolution mechanism, and the damage of rock mass and supporting time sure have been the key issues to be resolved in the deep underground engineering excavation. Based on these, this article follows the route from phenomenon to essence research, the mechanism of drilling and blasting method and tunnel boring machine (TBM) excavation method under the damage characteristics of rock mass and rock mass response of test parameters will be analyzed, the main research is as follows:(1) For the in-situ test of the excavation damaged zone under deep buried tunnel, the complementary advantaged and integrated in-situ test method based on the excavation damage zone is proposed of using elastic wave test technology, digital borehole camera technology, sliding micrometer deformation monitoring, seismic and acoustic emission signal positioning micro burst technology, the testing principle of the excavation damaged zone is illustrated. The experiment site selection principles, experiment platform construction method, drilling layout basis, test process, test equipment installation and debugging, and data processing methods are given. These design procedures make up for a single test methods not guaranteeing the validity of the test results, the construction way of diversity, and the complex and deep rock mass mechanics response of completeness of rock mass mechanics response of the completeness of information. Then, the in situ test design of deep buried tunnel excavation damaged zone of the Jinping secondary hydropower station was take for example to illustrates the in-situ test methods of EDZ.(2) Formation of disk-shaped rock cores is the process of cores damaged evolution with the local stress relieving under the deep buried rock mass. Based on the core macroscopic fracture morphology types summarized, the quantity and thickness of discs along the direction of distribution are given. What is more, the buried depth, geological structure, rock mass excavation damaged, the hole of diameter size and direction, and the drilling speed impact on rock discs were further explained. Simultaneously, by applying scanning electron microscope technique for different diameter, different thickness and concave and convex surface and different positions of rock cores, the micro-damage mechanism was discussed.(3) For the evolution and formation mechanism of excavation damaged zone drilling and blasting method under deep buried tunnel, based on understanding the mechanism of rock blasting, the failure mode and damaged cause of cave walls were summarized during the excavation of scientific research tunnels in the auxiliary tunnel by drilling and blasting method. Considering different buried depth, the size of the tunnel and the excavation method, through the digital borehole camera, the paper analyzed the damage of rock mass fracture characteristics and fracture occurrence before and after the excavation, and the change rule of crack width with the evolution law of the excavation process, and as well as the new crack along the drilling axial distribution rule with time. Wave velocity of rock mass under different time is obtained by acoustic testing, along the drilling direction of distribution, and the average wave velocity in the bottom of the bore is given along with the change of constraints. By sliding micrometer deformation test, the relationship of rock deformation with time and speed of change were presented. By micro seismic monitoring, seismic index, time, energy according to the relationship between footage changes over time, as well as the micro seismic events as constraints on the evolution of the law were given. Based on the analysis method of the above information, the evolution and formation mechanism of excavation damaged zone for drilling and blasting method was formed. At last, the axial and radial impact range, and time effect are respectively given, supporting design advice for the deep buried tunnel by drilling and blasting method excavation.(4) For the evolution and formation mechanism of excavation damaged zone TBM method under deep buried tunnel, based on understanding the mechanism of TBM. Through the digital borehole camera, the paper got the structure characteristic of the original rock mass, analyzed the damage of rock mass fracture characteristics and fracture occurrence before and after the excavation, and the change rule of crack width with the evolution law of the excavation process, and as well as the new crack along the drilling axial distribution rule with time. By acoustic emission testing, acoustic emission incidents and energy according to the relationship between footage changes over time were given. Through single-hole acoustic test, drilling damaged depths of some holes have been achieved. Based on the analysis method of the above information, in combination with surrounding rock stress state and stress strain curve, the evolution and formation mechanism of excavation damaged zone for TBM method was formed. In addition, the axial and radial impact range, and time effect are respectively given, supporting design advice for the deep buried tunnel by TBM.(5) Based on the numerical simulation method, the influence of the confining pressure on tunnel initial damage and critical damage condition were analyzed, and the influence of tunnel size on the deformation of surrounding rock as well. Making use of in situ test and other test results for surrounding rock parameters inversion, applying degradation of strength damage constitutive model, the deep buried tunnel numerical calculation model is established. Comparing the results of numerical simulation with field of surrounding rock mass, the rock damage degradation mechanical constitutive model (RDM), the mechanical parameters and FAI evaluation method are effective.