IN SITU DETERMINATION OF ELASTIC MODULI OF PAVEMENT SYSTEMS BY SPECTRAL-ANALYSIS-OF-SURFACE-WAVES METHOD (THEORETICAL ASPECTS). INTERIM REPORT

The Spectral-Analysis-of-Surface-Waves (SASW) method is an in situ testing method for determining shear wave velocity profiles of soil sites and stiffness profiles of pavement systems. The method is nondestructive and is performed entirely from the pavement or ground surface. Measurements are made at strains below 0.001 percent where elastic properties of the materials are independent of strain amplitude. The key elements in SASW testing are the generation and measurement of surface waves. Transient impacts containing wide ranges of frequencies are transmitted to the pavement surface by means of simple hammers. Surface waves generated by these impacts are captured and recorded by the receivers using a spectral waveform analyzer. The analyzer is used to transform the waveforms into the frequency domain and then to perform spectral analyses on them. The points of interest from this operation are the phase information of the cross power spectrum and the coherence function. By evaluating the coherence function during testing, the range of frequencies which is not contaminated with random background noise can be quickly identified. Phase information from the cross power spectrum is indicative of the relative phase shift of each frequency propagating between the receivers. By knowing the distance between receivers and the phase shift for each frequency, phase velocity and wavelength associated with that frequency are calculated. One of the most important steps in SASW testing is the inversion process which has been the missing link in engineering applications. The theoretical foundation of the SASW method is discussed in detail in this report, with an emphasis placed on the theoretical aspects of the inversion process.

• Supplemental Notes:
  • Research study title: Utilization of Surface Wave System for Measuring Moduli of Pavements.
• Corporate Authors:

  University of Texas, Austin

  Center for Transportation Research, 3208 Red River Street
  Austin, TX  United States  78705

  Texas State Department of Highways & Public Transportation

  Transportation Planning Division, P.O. Box 5051
  Austin, TX  United States  78763

  Federal Highway Administration

  1200 New Jersey Avenue, SE
  Washington, DC  United States  20590
• Authors:
  • Nazarian, S
  • Stokoe II, K H
• Publication Date: 1986-11

Media Info

• Features: Figures; References; Tables;
• Pagination: 134 p.

Subject/Index Terms

• TRT Terms: Field tests; Frequency analyzers; Modulus of elasticity; Nondestructive tests; Pavements; Rayleigh waves; S waves; Spectrum analysis; Stiffness; Theory; Velocity; Waveform analysis; Wavelength
• Candidate Terms: Spectral analysis of surface waves
• Uncontrolled Terms: Inversion process
• Old TRIS Terms: Ground profile; Insitu methods; Phase velocity; Velocity spectrum; Waveform
• Subject Areas: Design; Geotechnology; Highways; Pavements; I22: Design of Pavements, Railways and Guideways; I42: Soil Mechanics;

Filing Info

• Accession Number: 00473174
• Record Type: Publication
• Report/Paper Numbers: FHWA/TX-87/46+437-2, Res Rept 437-2, CTR 3-8-85-437-2
• Contract Numbers: Study 3-8-85-437
• Files: TRIS, USDOT, STATEDOT
• Created Date: Sep 30 1987 12:00AM