The Shear Wave Velocity Profiles Database

Shear wave velocity (Vs) profiles are needed for site response analyses and liquefaction susceptibility assessments. This database is a collection of Vs profiles from all curated projects in the NEES Project Warehouse, as well as some non-NEES projects. Shear wave profiles are often determined via in-situ methods such as cross-hole testing, downhole testing, suspension logging testing, and active and passive surface wave testing. With large mobile shakers available at the NEES@UTexas Equipment Site, shear wave velocity can be measured to a great depth using both downhole and active surface wave methods. The majority of Vs profiles available in this database were measured using the Spectral-Analysis-of-Surface-Waves (SASW) method. The SASW method is a well established active source surface wave measurement that utilizes Rayleigh waves to determine shear wave velocity profiles. The basis for the SASW method is the dispersive characteristic of Rayleigh waves when they are propagating in a layered system (i.e. soil or rock layers). Dispersion is the variation of velocity with frequency and it arises when waves of different wavelengths travel through different layers of the subsurface. High-frequency (short wavelength) waves propagate only through near-surface materials. Lower-frequency waves with longer wavelengths propagate through the near-surface as well as deeper soils. The SASW testing involves generating surface waves with a vertical excitation and then measuring the vertical surface motions. Receivers are arranged in a straight line which stretches outward from the source. The variation in phase shift with frequency for surface waves propagating between adjacent receivers is recorded for each receiver spacing. From each receiver pair, the phase velocity of the surface wave can be calculated. The phase velocity, VR, depends primarily on the material properties (shear wave velocity, mass density, and Poisson's ratio or compression wave velocity) over a depth of approximately one wavelength. From this calculation, a plot of phase velocity versus frequency, called a dispersion curve, is generated. This procedure is repeated for all source-receiver spacings used at the site and usually involves significant overlapping in the dispersion data between adjacent receiver sets. The individual dispersion curves from all receiver spacings are combined into a single composite dispersion curve called the experimental or field dispersion curve. A forward-modeling procedure is then used to match the field dispersion curve with a one-dimensional layered system of varying layer stiffnesses and thicknesses. The shear wave velocity profile that generates a dispersion curve that most closely matches the field dispersion curve is then presented as the shear wave velocity profile for the site.

剪切波速（Shear wave velocity, Vs）剖面是开展场地响应分析与液化势评估的必备参数。本数据集收纳了NEES项目仓库（NEES Project Warehouse）中所有精选项目的剪切波速剖面，以及部分非NEES项目的同类剖面。剪切波剖面通常通过跨孔试验、下孔试验、悬浮测井试验、主动与被动面波测试等原位测试方法获取。依托NEES@德克萨斯大学设备场地配备的大型移动式激振设备，可通过下孔法与主动面波法实现大深度剪切波速测量。本数据库中绝大多数剪切波速剖面均采用面波频谱分析法（Spectral-Analysis-of-Surface-Waves, SASW）测得。面波频谱分析法是一种成熟的主动震源面波测试技术，通过利用瑞利波（Rayleigh waves）反演获取剪切波速剖面。该方法的理论基础是瑞利波在层状体系（即土层或岩层）中传播时的频散特性。频散指波速随频率发生变化，其产生原因为不同波长的波会穿过地下不同深度的地层：高频（短波长）波仅能传播至近地表层，而低频（长波长）波则可穿透近地表并深入更深土层。面波频谱分析法的测试流程为：通过竖向激振产生面波，随后采集地表竖向振动信号。检波器沿震源向外呈直线排列，记录相邻检波器之间面波传播的相移随频率的变化关系，进而可由每对检波器的观测数据计算出面波相速度VR。面波相速度VR主要取决于约一个波长深度范围内的岩土体物性参数，包括剪切波速、质量密度、泊松比或压缩波速。基于上述计算结果，可绘制相速度与频率的关系曲线，即频散曲线。针对现场采用的所有震源-检波器间距重复上述测试流程，且相邻检波器组的频散数据通常存在显著重叠。将所有检波器间距对应的单条频散曲线整合为一条复合频散曲线，即试验频散曲线或现场频散曲线。随后通过正演模拟流程，将现场频散曲线与由不同刚度与厚度土层组成的一维层状体系进行拟合匹配，最终选取能够生成与现场频散曲线拟合度最高的剪切波速剖面，作为该场地的剪切波速剖面。