地震作用下黄土暗穴的稳定性分析

【作者】 陈立伟；

【导师】 范文；

【作者基本信息】 长安大学 ， 地质工程， 2004， 硕士

【摘要】 随着我国西部黄土地区基础建设的进行，发育在黄土浅层的暗穴对公路工程设施的危害日益明显和严重。黄土暗穴的稳定性不仅与黄土自身的工程地质特性有关，而且还与各种自然条件及人为因素有关。我国的黄土地区大部分处于地震多发区或受地震影响区，因此本文针对黄土暗穴可能遭受地震荷载的影响采用动力有限元方法进行了响应分析。 地震作用下黄土暗穴的动力响应分析可视为土体中无支护与无衬砌的空洞在地震作用下的动力响应问题。首先根据暗穴在黄土地区的发育特点，进行了地质模型的概化，并结合黄土暗穴的埋深、洞径大小、地层情况等实际特征建立了一系列相应的分析模型。考虑到实际洞穴形状及便于寻求计算结果的规律性，暗穴横断面的形状采用拱形，并按一定的宽高比建模。其次对野外调查中取得的原状黄土试样的动三轴测试结果进行了统计分析，给出了动力有限元的模型材料参数。动三轴试验数据处理结果表明黄土的动弹性模量随动应变的增加而降低，动应力-应变符合双曲线规律，而阻尼比随应力应变的变化关系比较离散。最后通过弹塑性动力响应分析，得出了地震作用下暗穴周围关键部位的应力、位移及加速度峰值，并给出了部分节点的时程曲线。 分析中主要考虑洞径及埋深两因素的影响，依据计算结果总结出了不同洞径及埋深的暗穴在地震荷载作用下的动力响应规律及其致塌机理。通过计算，认为：地震荷载作用下，处于同一水平位置土层的水平加速度峰值基本相近。暗穴的存在对水平加速度峰值有一定的放大效应；暗穴洞径大小或埋藏深浅对地表位移幅值的影响不大；地震荷载作用下，暗穴的周壁产生应力集中，这是造成暗穴顶板坍塌的因素之一；对比于相同洞径的暗穴，埋深越浅，在地面处引起的应力幅值越大；对于埋深相同的暗穴，则当洞径越大时在地面处引起的应力幅值越大，这说明暗穴直径大、埋深浅时在遭受地震作用时最不易于稳定；地震发生时，往往造成的是暗穴结构稳定性的丧失，是突发性的。更多还原

【Abstract】 With the development of base buildings in western loess area, the damages, which induced by the hidden holes, developed in the shallow loess layer on highway engineering facilities become increasingly obvious. The stability of loess hidden holes not only relates to the engineering geology characteristics, but to all kinds of natural conditions and human factors. The great masses of loess areas in our country come within the areas where earthquakes often take place. Considering the influence of earthquake load on loess hidden holes and by using the finite element method, the dynamic response has been analyzed in this paper.Dynamic response of loess hidden holes subject to earthquake can be seen as a hollow hole without any bracing. Firstly, according to the development characteristics of loess hidden holes, the geological models are summarized. And the corresponding geometrical mechanics models are established by integrating to the buried depth of loess hidden holes and the hole’s diameter dimension. The bottom of the model is regarded as an imaginary basement rock’s surface. Considering the thickness of the loess covering, the model’s border is decuple away from it to avoid the summation of the reflected wave. Considering the practical shape of holes, and to seek the regularity of calculation result, the arch with the same width and height is adopted as the cross section of hidden holes. Secondly, by analyzing the dynamic testing results of the primitive loess in Dingxi, the material parameters that used in the dynamic finite element method are given. The sine wave is used in dynamic test. The results evince that the dynamic elastic module become decline but the dynamic stress become rise. The curves of dynamic strain-stress confirm to hyperbola. But the curve of damping ratio is discrete. Finally, using the elastic and plastic dynamic analysis gets the stress, the displacement and the acceleration peak value of the hidden hole’s key sections with the influences of earthquake. And then the time interval curves of sectional nodes are given.The two factors, diameter dimension and buried depth of holes, are mainly considered in the course of analysis. The dynamic response of hidden holes with different diameters and buried depths are summarized based on the calculation results. Pursuantly, the collapse mechanism of loess hidden holes with the influence of earthquake can be got. By calculating, we submit the solutions as follows: The soil layers with the same level attitude have the same horizontal peak accelerations, and the hidden holes can make the horizontal peak acceleration bigger. The diameter andburied depth of holes have a minute effect on the sacrificial displacement. When earthquake take place, the stress concentration will appear in the hidden hole’s episporium. The stability of hidden holes with small diameter and deep-buried depth is relatively fine. The forfeit of hidden holes subject to earthquake is sporadic.更多还原