Evaluation of Backfill Aggregate Properties

Details

• Creators:
  Alshibli, Khalid A. ; Elkenawi, Mohamed
• Corporate Creators:
  University of Tennessee, Knoxville
• Corporate Contributors:
  Tennessee. Department of Transportation ; United States. Department of Transportation. Federal Highway Administration
• Subject/TRT Terms:
  Aggregates Backfill Soils Evaluation Friction Angle Friction Factor Granular Soils Open Graded Aggregates Retaining Walls Shear Strain Shear Strength Soils By Properties Wall Backfill

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• Publication/ Report Number:
  RES2024-05
• Resource Type:
  Tech Report
• Geographical Coverage:
  United States ; Tennessee
• Edition:
  Final Report (8/1/23-3/31/26)
• Corporate Publisher:
  Tennessee. Department of Transportation
• Abstract:
  Open-graded granular backfill materials are widely used as retaining wall backfill due to their high shear strength, high permeability, ease to handle, and compaction characteristics. However, the current Tennessee Department of Transportation (TDOT) provisions assume a conservative angle of internal friction for backfill materials. The objective of this project was to assess the influence of mineralogy, morphology, and aggregate type on the density and shear strength of fill aggregates from a wide range of supply sources throughout Tennessee. A comprehensive testing program was conducted employing a special large-scale direct shear apparatus to test twenty-six coarse aggregates conforming to the #57 stone gradation, including crushed limestone and river gravel at normal stresses of 35, 70, 105, and 140 kPa and relative densities of 30% and 80%. Particle morphology was quantified using 3D X-ray micro-computed tomography (μCT), enabling the extraction of statistically robust descriptors of roundness, form, and sphericity. The results demonstrate that specific morphology parameters, particularly sphericity location, roundness scale, and form scale, have a measurable and consistent influence on the peak friction angle (ϕp), critical state friction angle (ϕcs), and dilatancy angle (ψ), regardless of the particle size and material origin (mineralogy). Incorporating the 3D morphological indices into linear and nonlinear regression models significantly improved the prediction of ϕp, ϕcs, and ψ across a broad range of granular materials. This report recommends new friction and dilatancy angles for backfill materials depending on the height of the retaining wall and proposes revising current TDOT SP624 provisions for backfill materials compaction and subsequently the backfill zone behind the retaining walls. The percentage reduction in the volume of backfill aggregates for the proposed guidelines is between 24% and 66% depending on the height of the wall and the thickness of its footing.
• Format:
  PDF
• Funding:
  74736
• Collection(s):
  Federal Aviation Administration
• Main Document Checksum:
  urn:sha-512:abb37c1566cc36fe9df810c2a5d5efeb3cb31fd7d4d1704b02544c524acd61cb0cc0d37db448b0c01ca771bc689b5683a74761602151bf32933655706b262552
• Download URL:
  https://rosap.ntl.bts.gov/view/dot/89742/dot_89742_DS1.pdf
• File Type:
  [PDF - 16.53 MB ]