Experimental Study Of The Dynamics Of Saturated Sand Subjected To Incident Seismic Waves

The simulation of seismic effects in indoor test frequently adopts the "simplified procedure for evaluating soil liquefaction potential" advanced by Seed. This simplified procedure only considers the shear stress due to the upward propagation of shear waves which can be simulated by one-way dynamic triaxial test or dynamic simple shear test. The result based on it has been widely used in project. Recently, more and more strong earthquakes have been occurred around the large cities. This type of earthquake is called earthquekes occurring directly beneath large cities. It is found that the source of this earthquake tends to be shallow. If the simplified procedure is still used to simulate the loading of earthquake, it would be unreasonable. Under this condition inclined seismic waves should be considered, and also including the effects of P wave. For this, this paper analyzes the stress response of the soil elements due to inclined seismic waves based on the wave theory. Further, experimental study on the dynamics of saturated sand subjected to the inclined seismic waves is performed.Based on the wave theory of elastic medium, the stress of the soil elements in the field subjected to the seismic wave has been derived, and the dynamic stress path obtained at the same time. It is found from analyzing the stress path that the shape of the stress path is a inclined oval due to inclined incident P wave or SV wave, and is a line subjected to the normal incidence of P wave or SV wave. When the incident frequencies of the two body wave is different if the incidence of them simultaneously, the stress path would be complex, but still be a inclined oval in other case. There is great influence of the incident angle,the incident frequency and the depth of the soil element on the shape of stress path.Secondly, the dynamics of saturated sand subjected to seismic waves is tested, the results show that there are some differences on the dynamic of the saturated sand when the normal incidence and oblique incidence of seismic waves, mainly in dynamic strength. Subjected to the vertical incidence of P wave, when the dynamic stress path is a horizontal line, the dynamic strength of sand is maximum. Subjected to the incidence of SV wave with incident angle 12°-15°, when the dynamic stress path is approximately a circle, the dynamic strength is minimum. Subjected to the vertically incident SV wave, when the dynamic stress path is a vertical straight line, the dynamic strength is between the two above, indicates that if the simplified procedure is still used to simulate the seismic loading o, in some cases, the result may be unsafe.