| Tunnel project belongs to the underground covert engineering. When there are unknown geological conditions ahead of construction, such badness geological bodies as faults, underground rivers, soft interlayer, karst, can easily cause to unexpected geological disasters, such as collapse, water gushing, mud dashing, rock burst, etc.. All these unexpected geological disasters not only delay the construction schedule, but also bring about equipment easily buried, staff bereavement, which cause to heavy losses for the national economy, people's lives and properties. Tunnel detection is foundation of the geological disaster prediction and prevention, and rock mass classification is the basis for stability evaluation and treatment project for the geological disaster. But during tunnel geological hazards detection ahead of construction by reflected wave method, wave field is abundant, overlapped, and very complex, which cause it is difficult to effectively identify and separate. Conventional scalar wave field disposal methods are difficult to satisfy the requirements of high-precision and high-resolution. At the same time, for lack of an effective and rational system to determine the level of rock mass, traditional methods of rock mass classification cannot manifest the small difference of factors and guide the construction. So it is difficult to meet the requirement for the disposal of geological disasters in the tunnel. Aiming to these problems, under jointly funded research projects of the Ministry of Communication and Hunan province, the author studies and discusses the staggered-grid finite-difference simulation of elastic wave in tunnel situation, migration imaging for multi-wave and multi-component data of the reflected wave, and tunnel rock mass classification by dynamic F-AHP method. Then the paper develops the below works:(1)After deriving the first-order coupled elastic equations of 2D particle velocity and stress and any order accurate time and space formulation of staggered-grid finite-difference scheme, and discussing the stability condition of staggered-grid finite-difference method and seismic wave numerical dispersion, the author discusses the free boundary conditions and artificial boundary conditions detailed aiming at the special observation system for detection ahead of tunnel by reflected wave method, and then derives its finite-different format. All these work could set the foundation for the tunnel seismic wave field forward simulation and the according program compiling.(2)Combining with Visual C++ and MATLAB programme design language, the author compiles detection forward procedures for any complex model of tunnel disasters. Then by applied into the forward simulation calculation of typical project geological models in tunnel such as fault, karst whole, and get the wave field snapshot and seismic record of the according models. In these results, it could clearly observe the kinematics and dynamics characteristics of primary wave, reflection wave, transmission wave and multiple wave of reflection. By analysis these forward record and wave field snapshot, it could understand the propagation regulation of seismic wave field more profundity, improve comprehension to tunnel seismic wave field snapshot and provide the technology support to the inversion interpretation.(3)For the tunnel wave field is very complex and it is difficult to identify and separation effectively, in traditional wave field disposal methods, the scalar-wave field disposal methods would affect the low accuracy of disposal, and it could not satify the forecast of geological disaster. Then aiming at characters of multi-wave and multi-component by reflected wave methods detection in tunnel, the author adopts the vector wave field method and implements reverse-time migration based on full wave equation in complex tunnel condition. It could more adapted detection and interpretation for complicated geological structures in tunnel.(4) Considering the characters of tunnel engineering, the author proposes an integrated methods for the initial velocity model construction by making use of geology-geophysics data, well data, tunnel engineering data and seismic records. After deriving the staggered-grid finite-difference scheme for inverse time calculation, the author compiles procedures and realized the reverse-time migration arithmetic for tunnel wave field. Then it is applied into the geological models and tunnel engineering, and gets the more accuracy and clearly inversion imaging effect, which can improve imaging resolution and conducive geological interpretation for reflection wave data in tunnel condition.(5)After analyzing the limitations of traditional methods of rock mass classification, combined with of tunnel geological disasters detection and prevention, the author adjusts impact factors of tunnel rock mass classification dynamically by AHP method, calculates factors weights by fuzzy math theory, and compiles procedures for the rock mass classification by dynamic F-AHP arithmetic. Then it is applied into the tunnel engineering. The results show that the method is closer to the actual situation during tunnel excavation than traditional RMR, which raise the accuracy of rock mass classification and can supply more sufficient basis for the evaluation and disposal of the tunnel geological disaster.
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