【作者】 丁浩；

【导师】 黄博； 陈云敏；

【作者基本信息】 浙江大学 ， 岩土工程， 2010， 硕士

【摘要】 室内试验对地震作用的模拟通常采用Seed的简化分析法,该方法仅考虑S波垂直向上传播的剪应力作用,并可用单向动三轴或动单剪仪来进行模拟,基于此,在工程上已经得到广泛的应用。近年来,地震频发,在大城市周边发生的强震亦是屡见不鲜,此类地震俗称城市直下型地震,研究发现,该型地震往往震源较浅,若仍采用Seed简化法来模拟此类地震,已不再合理,而应考虑地震波斜入射,且同时应考虑P波的影响。对此,本文根据波动理论对地震波斜入射情况下场地某深度处的土单元应力响应进行了分析,进而对斜入射地震波作用下饱和松砂的动力特性进行了室内试验研究。根据弹性介质波动理论推导了一组平行地震波斜入射时弹性场地中任意单元体的应力状态,并由此得到了地震波作用下在土单元体中产生的动应力路径,通过对动应力路径的分析研究,发现：P波、S波单独斜入射时,应力路径均表现为倾斜的椭圆,垂直入射时,则表现为一条直线；两者同时入射时,仅当两者的入射频率f不相同时,动应力路径较为复杂,其余情况仍为斜椭圆；入射波的入射角、入射频率及单元体所处深度对动应力路径的形状有较大的影响。其次,本文重点对Kc固结条件下,地震波作用下饱和砂土的动力特性进行了试验研究,结果表明：地震波垂直入射与斜入射时饱和砂土的动力特性存在一定的差异,主要表现在动强度上,不管是P波入射还是SV波入射,随着入射角的增加,饱和砂土的动强度均呈现出先减小、后增大的发展趋势；P波垂直入射时,动应力路径为一条水平直线,动强度最大,SV波以入射角12°-15°入射时,动应力路径近似为一个圆,动强度最小,而SV波垂直入射时,动应力路径为一条垂直直线,动强度介于上述两者之间,表明若采用Seed简化法来模拟地震荷载,在某些情况下,结果可能不安全。更多还原

【Abstract】 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.更多还原