The Research Of Stress Wave Propagation Through Heavily Defected Rock Mass Based On Numerical Manifold Method

Natural rock masses usually contain discontinuities such as joints and micro-fractures.In the area of geotechnical engineering,the dynamic load would generate and propagate through rock mass as the form of stress wave.The joints and micro-fractures may propagate because of the propagation of stress wave and the growth of fractures would lead to the destruction of rock mass and further induce geotechnical instability.In addition,the wave attenuation and wave dissipation occur when the stress wave propagating through defected rock mass.The research of stress wave propagation characteristics is of great importance to evaluate the stability of rock mass.Basing on the fact that there are large quantities of micro-fractures or joints in rock mass,it is necessary to study stress wave propagation through defected rock mass.Due to the existence of discontinuous structural plane,the rock mass is neither completely continuous medium nor completely discontinuous medium.The numerical manifold method(NMM)has its advantages on solving both continuous and discontinuous problems;therefore it is a suitable way to simulate the wave propagation through defected rock mass.This paper based on the research of domestic and foreign scholars,combined the theoretical analysis and numerical simulation,and gave a detailed study on the dynamic mechanical behavior of heavily defected rock mass and stress wave propagation characteristics.The detailed scopes of present research are outlined as follows:(1)By reading relevant literatures,the research status of dynamic mechanical behaviors of the defected rock mass and common numerical simulation methods by domestic and foreign scholars were summarized;the application of the numerical manifold method in the rock mechanics was especially emphasized.The key difficulties of stress wave propagation in defective rock mass were proposed.Based on the basic theory of stress wave propagation and numerical manifold method,the one-dimensional wave equation in viscoelastic medium,the displacement jump equation and the loop updating process of crack propagation were derived.(2)Aimed at the working condition that the discontinuities in the far field would not propagate,the numerical modeling of stress wave propagation though rock mass containing micro-fractures was carried out.Two parameters of micro-fractures(length and quantity)and one parameter of incident wave(frequency)were selected and the attenuation rate and effective velocity during stress wave propagation process were defined.By analyzing the numerical results of incident wave and transmitted wave,the influence of the micro-fractures and the incident wave parameters on the attenuation rate and the effective velocity was revealed.(3)The Fourier transform theory is introduced to calculate the analytical solution of attenuation coefficient and wave number in the frequency domain,which is used to analyze the strength of defected rock mass under dynamic loading.The influence of the length and quantity of micro-fractures,the frequency of incident wave and the frequency of harmonic wave on the attenuation coefficient and wave number were obtained-The results showed that the attenuation coefficient and wave number are the constitutive parameters of the rock masses,which are only related to the properties of rock masses but would not change with the change of external loading.(4)Aimed at the working condition that the discontinuities in the neighbor field may propagate,the research on the micro-fracture propagation in rock masses caused by stress wave was carried out.The influence of the dynamic propagation of stress wave on the stress field around the micro-fractures before the growth of micro-fractures was analyzed.The variation of stress distribution in the rock mass before and after the micro-fractures propagation was compared.According to the actual geometrical shape of underground caverns,a cavity blasting model with a pre-existing crack in surrounding rock was established.The visual result of crack propagation caused by blasting stress wave was obtained.Subsequently,the effect of new-existing crack on wave attenuation and displacement was analyzed.In this paper,the numerical simulation method was used to study the dynamic mechanical properties of the heavily defected rock mass under stress wave propagation,and this research provides a reference for safety evaluation of the geotechnical engineering.