This thesis evaluates some methods for the measurement of stiffness parameters of soils, with an emphasis on the use of bender element technology in obtaining the shear modulus. The experimental program consisted two primary stages. The beginning part of the experimentation was concerned with evaluating the behavior of bender elements, both free-standing and when applied to soil. For this case, experiments were performed on dry Ticino sand. It was concluded that the bender element tip geometry has a much greater impact than previously perceived, in particular with long, slender geometries sometimes creating directly-propagating compressional waves that interfere with the shear wave arrival detection. To reduce the uncertainty in signal interpretation, a specimen aspect ratio of 1 was adopted, with a minimum wavelength ratio of 2. The second part of the experimentation consisted of using bender elements on Boston Blue Clay, both intact samples as well as Resedimented Boston Blue Clay, created in the laboratory from processed powder. The results obtained from loading normally consolidated specimens were generally consistent and in good agreement with the literature. The unloading portion was observed to behaves differently as a function of maximum consolidation stress, with the shear modulus decreasing less during unloading as higher stress ranges are reached. In addition to the testing performed on soils, a parametric study was conducted on common materials including steel, aluminum, acrylic, and rubber in order to evaluate the results for stiffness parameters measured using extensometers, accelerometers, and ultrasonic P-wave transducers. With the conclusion of these experiments, the accelerometers were shown to have highly variable results, especially for shear wave velocity, while the other methods yielded relatively consistent, reliable results as compared to published values. Finally, a new design for a triaxial setup that enables integrated measurements of compressional and shear velocities in soil over a wide stress range is presented as groundwork for the characterization of the complete stiffness matrix of BBC.
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机译：本文评估了一些用于测量土壤刚度参数的方法，重点是使用弯曲元件技术获得剪切模量。实验程序包括两个主要阶段。实验的开始部分是关于评估弯曲器元件的性能，包括独立式和应用于土壤的弯曲器。对于这种情况，在干燥的提契诺州沙子上进行了实验。得出的结论是，弯曲元件尖端的几何形状具有比以前认为的要大得多的影响，特别是对于细长的几何形状而言，有时会产生直接传播的压缩波，从而干扰剪切波的到达检测。为了减少信号解释的不确定性，采用了1的样品长宽比，最小波长比为2。实验的第二部分包括在Boston Blue Clay上使用弯曲元素，包括完整样品和Resededmented Boston Blue粘土，是由实验室加工粉末制成的。从加载正常固结试样获得的结果通常是一致的，并且与文献有很好的一致性。观察到卸荷部分的行为与最大固结应力的函数不同，随着达到较高的应力范围，在卸荷过程中剪切模量下降的幅度较小。除了在土壤上进行的测试外，还对包括钢，铝，丙烯酸和橡胶在内的常见材料进行了参数研究，以评估使用引伸计，加速度计和超声P波换能器测得的刚度参数的结果。根据这些实验的结论，加速度计显示出高度可变的结果，尤其是对于剪切波速度，而与其他方法相比，其他方法产生了相对一致，可靠的结果。最后，提出了一种用于三轴装置的新设计，该装置能够对宽应力范围内的土壤中的压缩和剪切速度进行综合测量，以此作为表征BBC完整刚度矩阵的基础。
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