Stability Of Underground Engineering Based On The Energy Release Rate

In recent years, with the rapid development of China's national economy, underground works gained rapid development in China, showing the emerging situation. The stability of underground geotechnical engineering has always been one of the academic focus of the studv. Before the excavation of underground engineering rock mass stress state in three-and rock excavation will lead to changes in rock stress field, making the excavation of rock stress in the unloading direction of relaxation. The past, the general stability of underground works is to use the load method to study rock mechanics, due to continuous loading and unloading has a completely different stress paths, which both caused by the deformation and failure characteristics of rock there is Big difference, so follow the continuous loading strength theory to predict rock mass under excavation unloading in the mechanical properties and stability, is clearly unrealistic. In this paper, theoretical analysis, numerical simulation, laboratory experiment for the approach, engineering applications for the purpose of adding by triaxial, unloading test of rock under unloading conditions, the mechanical and deformation behavior and failure mechanism, the use of energy release rate index analysis of different excavation on the stability of underground works, combined with field data to carry out the appropriate engineering inspection work. Overall, the main contents of this paper and results are as follows:(1) the use of TAW-2000 computer controlled servo axis of rock pressure testing machine, on the conventional triaxial compression test diabase and unloading confining pressure triaxial tests; which exceeded the long-unloading test with loading of rock mechanical means; conditions of loading and unloading characteristics of rock mass deformation and strength characteristics of brittle extension of conversion law and failure mode were compared, found that the strong expansion of unloading caused a sudden failure of rock deformation is the root cause, in addition to Canada contained mainly in the destruction of the main shear failure mode, while the unloading conditions, the rock samples showed a significant tension-shear compound destruction, and the failure of loaded unload more damage than violent, more sudden.(2) loading and unloading conditions, micro-structure inside the rock failure process and damage is not the same. Instability of underground rock was mainly due to excavation unloading produce damage caused deterioration of rock, rock damage to a certain degree of deterioration caused by the development of rock instability. Because the different stress paths under the same conditions in the mechanical behavior of rock under unloading conditions with continuous loading is not the same, therefore, the continued strength theory to predict the continuous loading in the rock mass under excavation unloading mechanical properties and stability, is clearly unrealistic. This experiment proved that the process of unloading rock mass deformation modulus "E" and Poisson's ratio "μ" decreased gradually increased, the elastic modulus "E" decreased by about 3.4% to 7.7%, while the lowest increase of approximately 13.5% "μ", The maximum increase of 65%, the change rate increases with increasing initial confining pressure and unloading larger degree of enhancement; addition, the relatively conventional compression tests, unloading rock mass friction angle "(?)" increases the cohesion "c" greatly reduced. These results show that the test will be obtained by means of unloading rock mass parameters for the calculation of more underground excavation engineering. (3) Test and conventional triaxial loading through unloading test of the rock sample confining pressure at different failure modes and damage levels, from the perspective of energy to explain the destruction of failure of loaded and unloaded belong to totally different stress path; indicating that the larger the unloading occurs, the more energy released, the higher the energy release rate, with the release of energy, rock damage increased degradation, stability gradually decreased to a certain extent, the sudden destruction. Based on the above experimental phenomena, proposed by different high-span ratio (H/B) to determine the Swallow Cliff tunnel excavation program, the energy release rate index used to optimize the results show that the excavation cross-section ratio is not high, the excavation around the circumference by The clip made the big rock, rock a certain extent unloading constraints, then the energy release rate is not high, are somewhat stable rock; In contrast, with the one-time increase in the amount of excavation, rock unloading more freely, energy release rate increases rapidly, reduce the degree of stability of surrounding rock and more apparent. Show a high degree of control excavation and excavation reasonable amount of makes sense to improve the stability of surrounding rock.(4) For underground projects, the excavation of rock energy release rate due to greater degradation of the more serious the injury of surrounding rock, the lower its stability, whereas the more stable. Text by Victoria-German highway tunnel cliff swallows the special geological conditions and construction environment as the background, using FLAC software for the tunnel excavation unloading simulation, comparative analysis of different wall rock excavation unit under the program of energy release rate, the use of The index assessing the stability of underground rock, and then optimized excavation scheme, and by the energy release, the average energy release rate and the traditional indicators of the plastic zone volume shows its scientific. Indicators of the final selection by the energy release rate in the excavation program II cliff swallows to get the actual tunnel construction applications, the paper further use of the surrounding rock of tunnel construction site level convergence and crown settlement amount of the value of the simulation results were compared with the measured results and simulation results in good agreement with simulation to obtain the maximum displacement value and the occurrence site and the site close to the actual situation.