Theoretical And Numerical Study On Dynamic Stress Path Induced By Obliquely Incident Seismic Waves

The dynamic stress path generated by the seismic actionis is the key issue for the study on evolution of the mechanical properties of the rock mass in the earthquake disaster. In soil dynamics,earthquakes are commonly simplified as vertically incident shear waves and the seismic stresses in soil are estimated based on rigid foundation model according Seed's simplified procedure. Strong earthquakes happened frequently in recent years. Characteristic of dynamic stress path is still not clear under seismic waves with significant oblique incidence and the great effect of P-waves should not be overlooked. Based on wave theory,the form of dynamic stress path induced by oblique incident P wave and SV wave and its influencing factors are analysed through mathematical derivation,parameter analysis and numerical simulation in this paper. The main work and conclusions are as follows:1. Analytical formulas of the seismic stresses and stress paths at any depth of semi-infinite elastic space under single obliquely incident P-waves or SV-waves are driven. The stress path proves mathematically an oblique ellipse in the plane consisting of two shear stress components(normal stress difference and horizontal shear stress). Under specific combination of parameters of seismic waves and Foundation material, the form of oblique elliptical stress path can be quite diverse, such as in shape of a straight line or a circle which can be regonized as a special case of oblique ellipses.2. Possible variation range of oblique elliptic stress path is systematically analyzed, which points out that incident angle, Poisson's ratio, and depth corresponding to unit wave length are the fundamental factors affecting stress path. Under oblique incidence, seismic stress level is likely to be higher. When incident angle of P-waves is in the range of 30 ? 60°, the amplitude of the seismic deviator stresses approach the largest value. When incident angle of SV-waves is between 20 ? 40°, the seismic stresses generated in the near saturated soil is the largest.3. Based on damping (quiet) artificial boundary of the FLAG finite difference software, the dynamic loads input of the oblique incident seismic wave is realized, and the dynamic responses generated by the P-waves or SV-waves in the layered foundation or one with underground cavern are simulated. And the influence of complex site conditions on dynamic stress response is discussed. The results show that the shape of elliptic stress path within the soft interlayer in corresponding layered foundation changes obviously from that in upper-soft and below-rigid foundation, tending to approach the horizontal ellipse, and interlayer possesses the highest possibility of liquefaction. The dynamic stress response of the foundation with underground cavern is very different from that without caverns, but the difference in the soil above the cavern is the smallest. The influence range of this difference is greater than the distance of the diameter of the cavern, and with the increase of stiffness of the foundation, this range will be expanded correpondly.