小应变剪切模量附加衰减对场地地震动力响应影响研究
发布时间：2018-08-19 10:47
【摘要】：小应变剪切模量Gmax是场地地震响应分析中的重要参数。在以往的场地地震响应有效应力分析法中,通常假定循环振动作用过程中土体的Gmax等同于相同有效应力静力状态下的Gmax,采用Hardin公式计算Gmax。而Hardin公式是根据土体静力状态下的试验所得到的,只考虑了有效应力和孔隙比等参数对Gmax的影响,未考虑循环振动历史这一重要因素。但已有的研究表明,在地震动中大应变幅振动将导致Gmax附加衰减,即地震过程中Gmax要比相应有效应力下Hardin公式计算得到的Gmax还要低,这部分由于地震振动导致的Gmax与静力状态下Gmax的区别,被称为附加衰减。目前,尚未有人探讨这种由于地震振动作用而产生的Gmax附加衰减给场地地震响应带来的影响。 本文在回顾前人对各类土体Gmax受大振幅振动影响研究的基础上,得到了对应于强结构性土和弱结构性土的两种不同Gmax附加衰减模式。将附加衰减模量值GmaxⅡ与相同有效应力下静力状态的小应变剪切模量值GmaxⅠ之比作为参量进行分析发现,弱结构性土和强结构性土的模量比GmaxⅡ/GmaxⅠ与有效应力比σm'/σm0'。的关系可分别用两段式和三段式来表示,文中拟合得到了不同衰减模式对应的数学表达式。 通过编制可考虑Gmax附加衰减影响的一维场地地震响应分析程序,对典型场地地震响应进行了分析对比。结果发现：Gmax附加衰减对场地加速度和剪应力响应均有较大影响,并将加速场地液化、扩大场地最终液化范围。地表加速度谱分析表明,考虑Gmax附加衰减后土体更加软化,对地震波短周期部分有减震作用,对长周期部分有加震作用。此外,文中还考察了场地条件和输入波卓越周期的影响,发现Gmax附加衰减对场地地震响应的影响程度随地下水位下降而增强,随场地土层厚度的增加无明显变化；强结构性土场地受到的影响比弱结构性土场地更大；不同卓越周期输入下均表现出由于Gmax附加衰减加快场地液化的现象。 为进一步考察Gmax附加衰减对场地地震响应的影响,采用该程序模拟分析了饱和砂土场地的离心机振动台模型试验。为获得离心机振动台试验所采用福建砂的孔压模型参数,进行了排水条件下等剪应变幅扭剪试验和压缩回弹试验,得到应变型孔压模型中计算体应变增量Δεvd和土体回弹模量Er的试验参数。通过对不同幅值地震加速度输入下模型场地动力响应的数值模拟,并和试验结果比较,两者所得加速度响应吻合得很好,孔压响应存在数值模拟中孔压增长慢于试验实测结果的现象,认为可能是由于离心机振动台试验模型边界和确定孔压参数的试验中空心圆柱试样边界不同造成的；两者所得土层液化深度及各层达到液化的时间均较为相符。考虑Gmax附加衰减对模型场地的影响,得出：当输入峰值加速度较小时,Gmax附加衰减对场地地震响应有显著影响；当场地输入峰值加速度较大时,由于场地迅速发生液化,Gmax附加衰减对场地地震响应影响减弱甚至无影响。
[Abstract]:Small strain shear modulus Gmax is an important parameter in site seismic response analysis. In the past effective stress analysis of site seismic response, it was assumed that Gmax of soil was equivalent to Gmax of the same effective stress static state in the process of cyclic vibration. Hardin formula was used to calculate Gmax. Hardin formula was based on the static state of soil. However, previous studies have shown that large strain amplitude vibration during earthquake will lead to additional attenuation of Gmax, that is, Gmax is calculated by Hardin formula under the corresponding effective stress than under the corresponding effective stress. The difference between Gmax caused by seismic vibration and Gmax under static state is called additional attenuation.
On the basis of reviewing the previous studies on the influence of large amplitude vibration on Gmax of various soils, two different additional attenuation modes of Gmax corresponding to strong structural soils and weak structural soils are obtained. The ratio of the additional attenuation modulus Gmax II to the small strain shear modulus Gmax I under the same effective stress is taken as a parameter. It is found that the relationship between modulus ratio Gmax II/Gmax I and effective stress ratio_m'/_m 0'. of weak and strong structural soils can be expressed by two-stage and three-stage formulas respectively. The corresponding mathematical expressions of different attenuation modes are obtained by fitting.
The seismic response of a typical site is analyzed and compared by compiling a one-dimensional seismic response analysis program which can consider the effect of additional attenuation of Gmax. The results show that the additional attenuation of Gmax has great influence on the site acceleration and shear stress response, and will accelerate the site liquefaction and expand the final liquefaction range of the site. It is shown that the soil softens more after considering the additional attenuation of Gmax, which can reduce the short-period part of seismic wave and increase the long-period part. In addition, the influence of site conditions and the predominant period of input wave is also investigated. It is found that the influence of additional attenuation of Gmax on the seismic response of the site increases with the decrease of groundwater level and with the site. The increase of soil thickness has no obvious change; the influence of strong structural soil is greater than that of weak structural soil; the liquefaction of site is accelerated by Gmax additional attenuation under different predominant period input.
In order to further investigate the effect of Gmax additional attenuation on the seismic response of the site, the centrifuge shaking table model test on saturated sand site is simulated and analyzed by using the program. The test parameters for calculating the increment of volume strain______________ The phenomena of the measured results may be due to the difference of the boundary between the centrifuge shaking table test model and the hollow cylindrical specimen in the test to determine the pore pressure parameters. When the peak acceleration is small, the additional attenuation of Gmax has a significant effect on the seismic response of the site; when the input peak acceleration is large, the impact of the additional attenuation of Gmax on the seismic response of the site is weakened or even no effect due to the rapid liquefaction of the site.
【学位授予单位】：浙江大学
【学位级别】：硕士
【学位授予年份】：2013
【分类号】：TU435
本文编号：2191436
[Abstract]:Small strain shear modulus Gmax is an important parameter in site seismic response analysis. In the past effective stress analysis of site seismic response, it was assumed that Gmax of soil was equivalent to Gmax of the same effective stress static state in the process of cyclic vibration. Hardin formula was used to calculate Gmax. Hardin formula was based on the static state of soil. However, previous studies have shown that large strain amplitude vibration during earthquake will lead to additional attenuation of Gmax, that is, Gmax is calculated by Hardin formula under the corresponding effective stress than under the corresponding effective stress. The difference between Gmax caused by seismic vibration and Gmax under static state is called additional attenuation.
On the basis of reviewing the previous studies on the influence of large amplitude vibration on Gmax of various soils, two different additional attenuation modes of Gmax corresponding to strong structural soils and weak structural soils are obtained. The ratio of the additional attenuation modulus Gmax II to the small strain shear modulus Gmax I under the same effective stress is taken as a parameter. It is found that the relationship between modulus ratio Gmax II/Gmax I and effective stress ratio_m'/_m 0'. of weak and strong structural soils can be expressed by two-stage and three-stage formulas respectively. The corresponding mathematical expressions of different attenuation modes are obtained by fitting.
The seismic response of a typical site is analyzed and compared by compiling a one-dimensional seismic response analysis program which can consider the effect of additional attenuation of Gmax. The results show that the additional attenuation of Gmax has great influence on the site acceleration and shear stress response, and will accelerate the site liquefaction and expand the final liquefaction range of the site. It is shown that the soil softens more after considering the additional attenuation of Gmax, which can reduce the short-period part of seismic wave and increase the long-period part. In addition, the influence of site conditions and the predominant period of input wave is also investigated. It is found that the influence of additional attenuation of Gmax on the seismic response of the site increases with the decrease of groundwater level and with the site. The increase of soil thickness has no obvious change; the influence of strong structural soil is greater than that of weak structural soil; the liquefaction of site is accelerated by Gmax additional attenuation under different predominant period input.
In order to further investigate the effect of Gmax additional attenuation on the seismic response of the site, the centrifuge shaking table model test on saturated sand site is simulated and analyzed by using the program. The test parameters for calculating the increment of volume strain______________ The phenomena of the measured results may be due to the difference of the boundary between the centrifuge shaking table test model and the hollow cylindrical specimen in the test to determine the pore pressure parameters. When the peak acceleration is small, the additional attenuation of Gmax has a significant effect on the seismic response of the site; when the input peak acceleration is large, the impact of the additional attenuation of Gmax on the seismic response of the site is weakened or even no effect due to the rapid liquefaction of the site.
【学位授予单位】：浙江大学
【学位级别】：硕士
【学位授予年份】：2013
【分类号】：TU435
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