THE EFFECTS OF WETTING AND DRYING ON THE LONG-TERM SHEAR STRENGTH PARAMETERS FOR COMPACTED BEAUMONT CLAY. FINAL REPORT

This report describes results of a series of laboratory tests performed to understand better the strength properties of highly plastic clays used in the construction of embankments in Texas. Previous studies showed that such embankments failed by sliding many years (10-30) after construction and that the apparent shear strengths in the field were substantially lower than the long-term shear strengths determined on the basis of laboratory tests on compacted specimens. This report presents the laboratory procedures and results for several series of tests in which specimens of compacted Beaumont clay were subjected to repeated cycles of wetting and drying and then sheared to measure the shear strength parameters in terms of effective stresses. Results of the tests show that repeated wetting and drying can produce a significant reduction in the effective stress cohesion intercept. Factors of safety were calculated using the reduced laboratory strengths for an embankment which had failed. Although the computed factors of safety were still somewhat greater than unity, even using the reduced shear strengths due to wetting and drying, the factors of safety were significantly reduced by the effects of wetting and drying. Although the factors of safety were still somewhat higher than unity, this may have been caused by small amounts of scatter and uncertainty in the data, which is especially critical for the relatively low cohesion values involved (less than 100 psf). Further laboratory testing is needed to more fully reproduce and understand the effects of wetting and drying on the long-term strength properties of highly plastic clays.

• Supplemental Notes:
  • Research study title: Development of Design Practice and Procedures for Determining Embankment Slope Stability.
• 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:
  • Rogers, L E
  • Wright, S G
• Publication Date: 1986-11

Media Info

• Features: Appendices; Figures; References; Tables;
• Pagination: 146 p.

Subject/Index Terms

• TRT Terms: Cohesive strength; Compacted clays; Drying; Effective stress; Embankments; Failure; Field strength; Laboratory tests; Safety factors; Shear strength; Stability (Mechanics); Time duration; Wetting
• Uncontrolled Terms: Long term
• Old TRIS Terms: Cohesive values; Embankment stability
• Subject Areas: Geotechnology; Highways; Safety and Human Factors; I42: Soil Mechanics;

Filing Info

• Accession Number: 00473171
• Record Type: Publication
• Report/Paper Numbers: FHWA/TX-87/40+436-2F, Res Rept 436-2F, CTR 3-8-85-436-2F
• Contract Numbers: Study 3-8-85-436
• Files: TRIS, USDOT, STATEDOT
• Created Date: Sep 30 1987 12:00AM