Dynamic properties of champlain sea clays

众所周知，在加拿大东部地震活跃的地区，由于软土和基岩之间的巨大阻抗对比，尚普兰海沉积物(或‘Leda Clays’)特别容易产生放大的地面运动。然而，目前对乐达粘土的动力特性随频率或其循环阻力比的变化的了解是有限的；因此，这些影响对中到大应变水平下的地震波的衰减或放大以及这些细粒土的循环软化敏感性的重要性是不确定的。 这项为期3年的联合研究的目的是研究与乐达粘土中的阻尼、剪切波速和循环剪切强度有关的一些重要问题。该项目包括：1)详细的现场和实验室调查来自三个包括冰后细粒(粘土和粉土)的试验场的乐达粘土沉积的小应变和大应变的动力学性质；2)通过钻井、取样和对尚普兰海沉积物中的大量钻孔进行测试，确定在现场和实验室测量阻尼值的最合适的方法；3)研究现场阻尼值随土壤性质和地层边界的变化，以及实验室中的阻尼值和速度随应变水平的变化；4)用非共振的实验室方法评估这些性质的频率依赖程度；5)简单剪切荷载下循环抗力比的表征及其对加载方式和深度的依赖关系；6)与地震数据的比较，以查看这些阻尼值是否与实际地震数据的实测土岩谱比相匹配；7)如何通过使用这些动力参数和各种软件程序来最好地模拟软土的反应。

It is well-known that, in seismically-active regions of Eastern Canada, Champlain Sea sediments (or 'Leda Clays'), are particularly prone to amplified ground motions due to large impedance contrasts between soft soils and bedrock. However, the current knowledge on the variation of the dynamic properties of Leda Clays with frequency or their cyclic resistance ratios is limited; thus, there is uncertainty on how important these effects may be on both the seismic wave attenuation or amplification at moderate to large strain levels and the cyclic softening susceptibility of these fine-grained soils. The purpose of this 3-year joint study is to investigate a number of important issues surrounding damping, shear wave velocities and cyclic shear strength in Leda Clay. The project includes: 1)a detailed in situ and laboratory investigation of the dynamic properties at small and large strains of Leda clay deposits coming from three experimental sites involving post-glacial fine-grained (clay and silt); 2) a determination the most appropriate method of measuring damping in situ and in the laboratory through drilling, sampling, and testing of numerous boreholes in Champlain Sea sediments; 3) a study the variation of damping in situ with changing soil properties and stratigraphic boundaries, and variation of damping and velocity in the lab with changing strain levels; 4) an evaluation the level of frequency dependence of these properties using non-resonant laboratory methods; 5) a characterization of the cyclic resistance ratio under simple shear loading, and evaluation of its dependency on loading modes and depth; 6) a comparison with earthquake data to see if these damping results match measured soil-to-rock spectral ratios of real earthquake data; 7) how best to model soft soil response through use of these dynamic parameters and various software programs.