非饱和黄土动力特性及其对场地地震动参数的影响
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摘要
针对宁夏西吉地区不同含水率非饱和黄土进行动三轴试验,在分析含水率对黄土动力特性影响的基础上,采用土层地震反应分析方法研究地表黄土层含水率变化对黄土场地地面运动强度和特征的影响规律。研究表明,随着含水率的升高,土的动剪切模量逐渐减小,阻尼比逐渐升高,当含水率达到塑限时,含水率变化对其影响明显减弱;总体上,随着输入地震动强度的增大和含水率升高,黄土场地地表地震动PGA和反应谱值呈现增大的趋势;而含水率对不同场地的地面运动强度和特征的影响差异性较大,对于覆盖层较薄的场地,在含水率达到20%时,当输入加速度峰值大于50 gal时地震动放大倍数开始减小,随着输入地震动的增大,减小程度增大,而反应谱长周期分量上谱值增大;覆盖层较厚场地在输入加速度峰值300 gal时,20%含水率土层的放大倍数有所降低,但反应谱值在0.3 s之后明显增大。
The dynamic triaxial tests on the unsaturated loess in Xiji region of Ningxia under different water contents are carried out. Based on the analysis of the influences of water content on the dynamic characteristics of loess, the influences of water content of soil on the surface motion intensity and characteristics of a loess sites are studied by using the method of soil seismic response analysis. The results show that with the increase of water content, the dynamic shear modulus decreases and the damping ratio increases. When the water content reaches the plastic limit, the influences of change of water content are obviously reduced. On the whole, with the increase of input seismic motion and the increase of water content, the PGA and the values of reaction spectral in the loess site increase. And the influences of water content on the ground motion intensity and characteristics are different in different sites. For the thinner site, when the water content reaches 20%, and the input seismic motion is greater than 50 gal, the magnification begins to decrease, and with the increase of the input seismic motion, the decrease amplitude increases, while the value of the long period component of the reaction spectrum increases, and when the input seismic motion of thicker covering site reaches 300 gal, the magnification decreases when the water content reaches 20%,but the value of reaction spectra increased obviously after 0.3 s.
The dynamic triaxial tests on the unsaturated loess in Xiji region of Ningxia under different water contents are carried out. Based on the analysis of the influences of water content on the dynamic characteristics of loess, the influences of water content of soil on the surface motion intensity and characteristics of a loess sites are studied by using the method of soil seismic response analysis. The results show that with the increase of water content, the dynamic shear modulus decreases and the damping ratio increases. When the water content reaches the plastic limit, the influences of change of water content are obviously reduced. On the whole, with the increase of input seismic motion and the increase of water content, the PGA and the values of reaction spectral in the loess site increase. And the influences of water content on the ground motion intensity and characteristics are different in different sites. For the thinner site, when the water content reaches 20%, and the input seismic motion is greater than 50 gal, the magnification begins to decrease, and with the increase of the input seismic motion, the decrease amplitude increases, while the value of the long period component of the reaction spectrum increases, and when the input seismic motion of thicker covering site reaches 300 gal, the magnification decreases when the water content reaches 20%,but the value of reaction spectra increased obviously after 0.3 s.
引文
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[3]骆亚生,田堪良.非饱和黄土的动剪模量与阻尼比[J].水利学报,2005(7):830-834.(LUO Ya-sheng,TIANKan-liang.Dynamic shear modulus and damping ratio of unsaturated loess[J].Journal of Hydraulic Engineering,2005(7):830-834.(in Chinese))
[4]王志杰,骆亚生,王瑞瑞,等.不同地区原状黄土动剪切模量与阻尼比试验研究[J].岩土工程学报,2010,32(9):1464-1469.(WANG Zhi-jie,LUO Ya-sheng,WANF Rui-rui,et al.Experimental study on dynamic shear modulus and damping ratio of undisturbed loess in different regions[J].Chinese Journal of Geotechnical Engineering,2010,32(9):1464-1469.(in Chinese))
[5]王兰民,蒲小武,吴志坚,等.地震和降雨耦合作用下黄土边坡动力响应的振动台试验研究[J].岩土工程学报,2018,40(7):1287-1293.(WANG Lan-min,PU Xiao-wu,WUZhi-jian,et al.Shaking table tests on dynamic response of loess slopes under coupling effects of earthquakes and rainfalls[J].Chinese Journal of Geotechnical Engineering,2018,40(7):1287-1293.(in Chinese))
[6]宋丙辉.兰州黄土的动力特性及其场地地震动反应[D].兰州:兰州大学,2017.(SONG Bing-hui.Study on the dynamic properties of Lanzhou loess and associated site response analysis[D].Lanzhou:Lanzhou University,2017.(in Chinese))