Spectral Analysis of Surface Waves


  tech briefs

The Spectral Analysis of Surface Waves (SASW) method is applied to structural elements to estimate surface-opening crack depths, fire damage and freeze-thaw damage depths, and to measure relative concrete quality. It can also be used for thickness profiling of pavements, including asphalt and layer systems. The method uses the dispersive characteristics of surface waves to determine the variation of the shear wave velocity (stiffness) of layered systems with depth. Surface opening cracks, honeycomb zones, fire damage, and other flaws create an effective "layer" of low velocity material with depth which can be measured. Once the shear wave velocity profiles are determined, shear and Young’s moduli of the materials can also be estimated through the use of simple mathematical equations. The shear wave velocity profiles (shear wave velocity versus depth) are determined from the experimental dispersion curves (surface wave velocity versus wavelength) obtained from SASW measurements through a process called forward modeling or inversion process. The shear wave velocity measurements can be used to compare concrete areas to locate zones of weak or degraded concrete. The SASW method can be performed on any material provided there is an accessible surface for receiver attachments and source impacting.

NOTE: SASW measurements are accurate to within 5% for the determination of the thickness and stiffness of the top layer in a pavement system.

Applications of SASW include, but are not limited to, the following:
  • Determination of pavement system profiles including the surface layer, base and subgrade materials
  • Determination of surface opening crack depths
  • Freeze-Thaw damage depth measurement
  • Fire damage depth measurement
  • Determination of abutment depths of bridges
  • Condition assessments of concrete liners in tunnels, and other structural concrete conditions

Material Tested: Concrete, Asphalt, Soil, Rock, Masonry, and Wood