Verification of abutment and retaining wall design assumptions.

Details

• Creators:
  Gomez, Brian W. ; Dewoolkar, Mandar M. ; Lens, John E.
• Corporate Creators:
  University of Vermont. Department of Civil and Environmental Engineering
• Corporate Contributors:
  United States. Federal Highway Administration
• Subject/TRT Terms:
  • Bridge abutments
  • Retaining walls
  • Backfill soils
  • Cast in place structures
  • Fines (Materials)
  • Shear strength
  • Permeability coefficient
  • State departments of transportation
  • Recommendations
• Publication/ Report Number:
  2015-06
• Resource Type:
  Tech Report
• Geographical Coverage:
  Vermont
• Corporate Publisher:
  Vermont. Agency of Transportation. Research and Development Section
• Abstract:
  The American Association of State Highway and Transportation Officials (AASHTO), along with some other federal and state guidelines, ; suggest a maximum soil fines (particles finer than 0.075 mm) content in granular structural backfill be used behind bridge abutments and retaining ; walls. This fines content limit is currently set at 6 percent (by weight) by the Vermont Agency of Transportation (VTrans) and is usually between 5 ; and 12 percent in most states, according to a canvassing of state Department of Transportation (DOT) practices. The fines content limit is an ; attempt to assure a free-draining backfill condition so water is not retained behind the structure, thereby eliminating the need to design the ; abutments and retaining walls for hydrostatic pressures. It appears that this maximum fines content is adopted largely as a rule-of-thumb ; considering that hydraulic conductivity of a soil is expected to decrease with increasing fines content. In Vermont and many other regions the ; availability of high-quality structural backfill with naturally low fines content is declining, which warrants an evaluation of whether granular backfill ; materials with greater than 5% fines content could be successfully used in practice. ; This research project was set up with two broad over-arching goals. The first goal was to verify that the backfill and drainage details currently ; used in cast-in-place concrete cantilevered retaining walls and bridge abutments on VTrans projects perform as expected and that the backfill has ; the engineering properties assumed in the design. The second goal was to find the most cost effective backfill details. To evaluate the above two ; overarching goals, the specific objectives of this research were to: (1) survey other state Departments of Transportation on their practices for ; abutment and retaining walls; (2) study the effects of fines on a typical granular structural backfill by performing hydraulic conductivity and shear ; strength tests at varied non-plastic fines contents; (3) monitor differential water levels between the stream and the backfill at two field sites; (4) ; analyze the collected data and develop specific recommendations for VTrans; and (5) prepare this final report. ; To assess if any differential water pressures exist in existing cast-in-place reinforced concrete retaining walls installed by VTrans, a field ; monitoring program was implemented at two sites in Vermont. The laboratory investigation included flexible wall, hydraulic conductivity tests on a ; granular structural backfill with 0, 5, 10, 15, 20, and 25% non-plastic fines content at 41, 83, and 124 kPa (6, 12, and 18 psi) confining pressures ; followed by consolidated drained triaxial compression tests for obtaining associated drained shear strength parameters of these gradations. The ; 15.2 cm (6 in.) diameter specimens were prepared at optimum moisture content and 95% of maximum standard Proctor density. Some tests were ; conducted at 90% of maximum standard Proctor density. To enable a comparison with respect to modified Proctor maximum densities, modified ; Proctor tests were also performed for all base soil-fines content mixtures. The experimental results were compared with relevant studies found in ; the literature. ; The results of the field monitoring program were inconclusive. The results of the laboratory investigation indicated that a non-plastic fines ; content up to 10% may be justified in structural backfill specifications for retaining walls and abutments.
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• Format:
  PDF
• Funding:
  RSCH017-720
• Download URL:
  https://rosap.ntl.bts.gov/view/dot/28658/dot_28658_DS1.pdf
• File Type:
  [PDF - 3.67 MB]
• Collection(s):
  US Transportation Collection
• Main Document Checksum:
  urn:sha-512:32cf85f2ffb9076e7f773acaaba667c66797e8939d0166b48bbcd6014226e8d40b86b92f072acafb65316f5044de005415aa1cc0d2b2ab81f50f649ae479b6d3