Numerical Simulation And Separation Of Seismic Waves Based On Reformulated TSP Observation System

Abstract:In the process of tunnel excavation, geological hazards are very likely unexpected due to unknown geological conditions ahead of construction which could not only delay the construction schedule, but may also cause casualties and other security issues for the practitioner. Technique of tunnel detection forms the basis of the geological hazards prediction and plays an important role in preventing these hazards. Thus, the study of their theory and practice is of great significance. Among the tunnel geology prediction methods, the tunnel seismic prediction is the most widely used method.The following fundamental research works were carried out in this thesis with respect to the improved TSP measurement system.1. Firstly, the drawbacks of the conventional TSP geometries are illustrated, the author proposed a modified TSP observation device which is easy to implement, has little effect on tunnel construction and can obtain full-wave field information. Moreover, this device can easily acquire the observations of multiple coverage, which is quite useful in improving the signal-to-noise ratio of the material and accurately imaging and interpreting of complex geological medium.2. Combining the constitutive equation of elastic wave with Cauchy equation and Navier equation, the first-order rate-stress elastic wave equation was deduced. By using staggered grids, any even-order accurate time and space formulation of staggered-grid finite-difference formulae used in the forward modeling was also deduced.3. To study the algorithm and the geometry, two artificial geological models are constructed vertical fault and a single hollow. The author then developed MATLAB codes of forwarding simulation of wave field and single shot records for the models. The simulation results clearly show the characters of direct wave, reflected wave and the converted wave.4. The up-going and down-going, P-and S-wave fields were separated using3different ways:F-K filtering, τ-p filtering, P-and S-wave separation method based on polarization properties. I analyzed the effects of these methods. The result shows that F-K filtering, τ-p filtering are both capable to separate up-going and down-going wave fields. But they cannot separate P-and S-wave effectively. The method based on polarization properties has its unique advantages, especially outstanding for S-wave separation and applicable S-wave field extraction under complex geological conditions.Through improving the TSP observation device, implementing the forward modeling algorithm, and studying the separation methods of up-going and down-going, P-and S-wave fields, I demonstrate the great potential value of further application of this new device and related imaging methods in tunnel excavation.