DETERMINATION OF BEDROCK DEPTH FROM FALLING WEIGHT DEFLECTOMETER DATA

The accuracy of falling weight deflectometer (FWD) backcalculated moduli depends heavily on knowledge of bedrock depth. The bedrock depth can be obtained from coring, boring, and seismic refraction tests, but these operations are not practical. Determining the bedrock depth from FWD data is the easiest and least expensive way. This paper documents the effects of bedrock depth on FWD responses and makes comparisons between predicted bedrock depth and field measurements. Modified algorithms that better fit the field measurements are proposed. It was found that bedrock depth has a great influence on outer FWD sensor (r3 to r6) readings. Deeper bedrock resulted in a higher percentage of increase in r3 to r6 readings in response to increased load. When the r4 reading is less than 25.4 micrometers for any drop height, it is very likely that the bedrock is within 1.52 m of the surface. The time-deflection history patterns were drastically different between shallow and deep bedrock. When there is no free oscillation after the first deflection peak in a time-deflection history, shallow bedrock (within 1.52 m) is indicated. A modified equation (Equation 2) using the peak deflections provides an accuracy within 30%. It is recommended that these equations be used on a pavement where there is no severe surface distress. Another modified equation (Equation 6) using time-deflection history data yields an accuracy within 20% but cannot be used when there is no clear indication of free oscillation.

• Record URL:
  • https://doi.org/10.3141/1655-17
• Summary URL:
  • http://scholar.google.com/scholar_lookup?title=DETERMINATION+OF+BEDROCK+DEPTH+FROM+FALLING+WEIGHT+DEFLECTOMETER+DATA&author=D.+Chen&publication_year=1999
• Availability:
  • Find a library where document is available. Order URL: http://worldcat.org/isbn/0309070511
• Supplemental Notes:
  • This paper appears in Transportation Research Record No. 1655, Pavement Management Systems and Other Pavement Design Issues.
• Corporate Authors:

  Transportation Research Board

  500 Fifth Street, NW
  Washington, DC  United States  20001
• Authors:
  • Chen, D-H
• Publication Date: 1999

Language

• English

Media Info

• Features: Figures; References; Tables;
• Pagination: p. 127-134
• Serial:
  • Transportation Research Record
  • Issue Number: 1655
  • Publisher: Transportation Research Board
  • ISSN: 0361-1981

Subject/Index Terms

• TRT Terms: Accuracy; Algorithms; Bedrock; Depth; Equations; Falling weight deflectometers; Mathematical prediction; Measurement
• Subject Areas: Data and Information Technology; Design; Highways; Pavements; I22: Design of Pavements, Railways and Guideways; I23: Properties of Road Surfaces;

Filing Info

• Accession Number: 00769347
• Record Type: Publication
• ISBN: 0309070511
• Files: TRIS, TRB, ATRI
• Created Date: Aug 31 1999 12:00AM