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Influence of Site Conditions on Near-field Effects in Multi-channel Surface Wave Measurements.

机译：场地条件对多通道表面波测量中近场效应的影响。

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摘要

Geophysical measurements using surface wave methods (SWM) are in widespread use as a means to non-destructively and non-intrusively characterize geotechnical site conditions for a variety of applications. Surface wave measurements are used to develop shear wave velocity (Vs) profiles which are directly related to the small-strain shear modulus (G) of the soil, an important parameter for dynamic and static geotechnical analysis. One of the potential sources of error in SWM is the underestimation of surface wave velocity due to inaccurate measurements in the near-field, where the receiver array is located too close to the source. These near-field effects have been studied extensively for the two--channel SASW method, but few cases have been studied using multi-channel arrays. A recent criteria developed by Yoon and Rix (2009) for multi-channel measurements suggested that the normalized array center (NAC) distance (i.e. the number of wavelengths between the source and array center) should be 2 or greater. However, this finding conflicts with recent experimental data collected in the Mississippi embayment by Rosenblad and Li (2011), which showed near-field effects occurring at NAC values of about 0.5. The objective of this research is to investigate and explain this contradiction and better understand the factors influencing near-field effects. It is hypothesized that the primary reason for the discrepancy is different conditions of saturation (and hence, Poisson's ratio) in the Yoon and Rix (2009) study and the Rosenblad and Li (2011) study. Numerical simulations of surface wave propagation were performed for five synthetic V s profiles under different assumed saturation conditions. It was found that Poisson's ratio did have a significant influence on the required source offset distance to minimize near-field effects. However, the effect was complex and strongly influenced by the Vs profile. For the profiles considered, limiting NAC values ranged from about 2 to as low as 0.3. The lowest values were observed for cases of linearly increasing Vs with depth under saturated conditions. Simulation of surface wave measurements for a site in the Mississippi embayment produced results that were consistent with the experimental observations. The findings from this work have important implications on both the measurement procedures and inversion methods used in multi-channel surface wave methods.
机译：使用表面波方法（SWM）的地球物理测量方法被广泛用作一种无损和非侵入式地表征岩土工程现场条件的方法，可用于多种应用。地表波测量用于建立剪切波速度（Vs）剖面，该剖面与土壤的小应变剪切模量（G）直接相关，这是动态和静态岩土分析的重要参数。 SWM中潜在的误差源之一是由于近场中的测量不准确而导致的表面波速度的低估，因为近场中接收器阵列距离源太近。对于两通道SASW方法，已经对这些近场效应进行了广泛的研究，但很少有人使用多通道阵列进行研究。 Yoon和Rix（2009）针对多通道测量制定的最新标准表明，归一化阵列中心（NAC）距离（即光源和阵列中心之间的波长数）应为2或更大。然而，这一发现与Rosenblad和Li（2011）在密西西比河堤中收集的最新实验数据相矛盾，后者表明在NAC值约为0.5时发生了近场效应。这项研究的目的是调查和解释这种矛盾，并更好地了解影响近场效应的因素。假设差异的主要原因是Yoon和Rix（2009）研究以及Rosenblad和Li（2011）研究中饱和度的不同条件（以及泊松比）。在不同的假定饱和条件下，对五个合成的Vs剖面进行了表面波传播的数值模拟。发现泊松比确实对所需的源偏移距离有很大影响，以最大程度地减小近场效应。但是，效果很复杂，并且受Vs轮廓的影响很大。对于所考虑的配置文件，极限NAC值的范围从大约2到低至0.3。在饱和条件下，Vs随着深度线性增加的情况观察到了最低值。密西西比河内某地点的表面波测量结果的模拟结果与实验观察结果一致。这项工作的发现对多通道表面波方法中使用的测量程序和反演方法都具有重要意义。

著录项

  • 作者

    Li, Cheng-Hsuan.;

  • 作者单位

    University of Missouri - Columbia.;

  • 授予单位 University of Missouri - Columbia.;
  • 学科 Geotechnology.;Engineering Civil.;Engineering Geological.
  • 学位 M.S.
  • 年度 2011
  • 页码 218 p.
  • 总页数 218
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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