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首页> 外文期刊>Soil Dynamics and Earthquake Engineering >Monofrequency in situ damping measurements in Ottawa area soft soils
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Monofrequency in situ damping measurements in Ottawa area soft soils

机译：渥太华地区软土中的单频原位阻尼测量

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摘要

In Ottawa, Canada, unusually high amplification ratios have recently been measured in clayey silts (called 'Leda Clays') at low levels of earthquake-induced ground shaking. However, the contribution of seismic Q, or material damping (E = 1120), to the overall ground motion at soft soil sites across the city is not well understood. This research investigates attenuation measurements in soft soils (Vs < 250 m/s) for ongoing seismic hazard evaluation in the Ottawa area. The work focuses on in situ measurements of damping in two deep boreholes drilled into Leda Clay. To investigate the possibility of frequency-dependent dynamic properties of these materials at low strains, a new approach to the spectral ratio technique has been developed for the measurement of Qs in the field using a mono-frequency vibratory source (generating signals between 10 and 100 Hz), and two identical downhole 3-component geophones. Monofrequency signals also allowed for the measurement of dispersion (variation of velocity with frequency). Analysis of the data show that dynamic properties are, for the most part, independent of frequency in the homogenous silty soils, yielding negligible variation in shear wave velocity (<2m/s) across the frequency test band, and small strain Qs's ranging from 170 to 200 (damping of 0.25-0.30%) over soil thickness intervals ranging from 10 to 60 m. At intervals within 20 m of the ground surface, laminated silt and clay beds of elevated porosity are found to have slight influence on the frequency dependence of damping for frequencies greater than 70 Hz (damping increase to 0.6%).
机译：在加拿大渥太华，最近在低水平的地震引起的地震动下，在粘土质粉砂（称为“ Leda Clays”）中测得了异常高的放大率。但是，人们对地震Q或物质阻尼（E = 1120）对整个城市软土场地整体地面运动的贡献还知之甚少。这项研究调查了软土（Vs <250 m / s）的衰减测量，以进行渥太华地区的地震危害评估。这项工作着重于现场测量在Leda Clay中钻出的两个深井眼中的阻尼。为了研究这些材料在低应变下随频率变化的动态特性的可能性，已开发出一种新的频谱比技术，用于使用单频振动源在现场测量Qs（产生10至100之间的信号）。 Hz）和两个相同的井下3分量地震检波器。单频信号还允许测量色散（速度随频率的变化）。数据分析表明，动态特性在很大程度上与均质粉质土壤中的频率无关，在整个频率测试带上，剪切波速度（<2m / s）的变化可忽略不计，并且小应变Qs范围为170在10至60 m的土壤厚度范围内达到200至200（阻尼为0.25-0.30％）。在距地面20 m的间隔内，发现孔隙率升高的层积粉砂和黏土层对大于70 Hz的频率的阻尼频率依赖性影响很小（阻尼增加至0.6％）。

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