A Research Of Physics Experiments In Model Scale Effects

Rayleigh surface wave has widely used in shallow engineering geological exploration and engineering quality testing, and other fields, and achieved good exploration results. Laboratory physical simulation research is to recognize and transient whether more to the development of surface wave is one of the main means of the theory and method.In the transient surface wave in laboratory studies, often encounter the following two questions.1, Laboratory commonly used limited scale model of the excitation of the acoustic wave field and the actual dielectric semi-infinite space is quite different. Model to the transient whether more limited scale surface wave seismic record pick dispersion curve caused a great disturbance.2, For complex wave field distribution model which is not yet clear, will complicate the research problem, easy for the research question, the three-dimensional geological model often simplified as two-dimensional model to deal with, in order to reduce the difficulty to analyze the problem and save cost modeling. However, the conventional laboratory two-dimensional physical model is difficult to achieve. Research whether the three-dimensional model of a certain condition can replace two-dimensional model, and have similar wave field characteristics will have higher practical value.In view of the question 1, based upon the three-dimension numerical modeling by Finite Element Method, this article simulates the acoustic wave field excited in finite size models, and analyzes the characteristics of Rayleigh wave field in the sized models and the effects to picking up the dispersion curve. The researches show that the reflected Rayleigh waves from the both side interfaces of a model along with the observation layout are main interference factors to picking up the dispersion curve, and if the half wideness of the model is close or large over an order of magnitude (5-10 times) of the main wavelength of Rayleigh wave approximately, the interference could be deleted by the conventional processing method for Rayleigh waves. Moreover, the article also presents a method to reduced the interference based on the wave separation with τ-P translation without the need to enlarge the model size. Finally, an experiment case is given to verify the interference problem and the flexibility of the solution scheme illustrated in the article.In view of the question 2, based on the acoustic wave field finite element numerical simulation model for the numerical models of different thickness of excitation to simulate, study and analyze the three-dimensional homogeneous half space and lateral heterogeneity model with different thickness of Fresnel zone radius R Rayleigh surface wave field and dispersion characteristics, and the corresponding numerical simulation of 2D results were analyzed. Studies have shown that the model is less than the minimum thickness of the first Fresnel zone radius R condition, three-dimensional physical model test results are consistent with the experimental results of two-dimensional numerical simulation model. Therefore, in the actual physical simulation, available in a thickness less than the minimum three-dimensional physical model of the first Fresnel zone radius R approximate two-dimensional model. Finally, the numerical simulation of reasonable thickness of the model to determine the production of physical model experiments verify the feasibility of the proposed problems and solutions.