Nonlinear load-deflection behavior of abutment backwalls with varying height and soil density.

Details

• Creators:
  Stewart, Jonathan P. ; Taciroglu, Ertugrul ; Wallace, John W. ; Lemnitzer, Anne ; Hilson, Chris H. ; Nojoumi, Ali ; Keowan, Steve ; Nigbor, Robert L. ; Salamanca, Alberto
• Corporate Creators:
  University of California, Los Angeles. Dept. of Civil and Environmental Engineering
• Corporate Contributors:
  United States. Federal Highway Administration
• Subject/TRT Terms:
  • Bridge abutments
  • Backfill soils
  • Clay
  • Sand
  • Stiffness
  • Bearing capacity
  • Soil compaction
  • Deflection
  • Height
  • Walls
• Publication/ Report Number:
  CA12-2040
• Resource Type:
  Tech Report
• Geographical Coverage:
  California
• Corporate Publisher:
  California. Dept. of Transportation. Division of Research and Innovation
• Abstract:
  We address the scaling of abutment wall lateral response with wall height and compaction condition through testing and analytical work. The ; analytical work was undertaken to develop hyperbolic curves representing the load-deflection response of backwalls for two backfill material types ; (clay and sand) as a function of wall height. The scaling of backwall resistance with height is expressed by an exponent n applied to a normalized ; wall height; we find that the height scaling exponent can be taken as 1.05 and 1.56 for the considered clay and sand backfill materials. ; We tested two wall-soil specimens with identical characteristics except for the level of compaction of the sandy backfill. One specimen ; (denoted T8.0-1) has as-compacted relative densities ranging from approximately Dr = 0.4-0.6 (which was lower than specified) and the other (T8.0- ; 2) had a high level of compaction of Dr = 0.9-1.0. Other than the degree of compaction, the two specimens are essentially identical in terms of ; dimensions, material gradation, and boundary conditions imposed during testing. The wall height in these tests is 8.0 ft (2.4 m), which represents an ; approximate upper-bound backwall height; in previous work we tested a similar specimen with a height of 5.5 ft (1.67 m). The backfill material is a ; well graded silty sand known in the construction industry at SE-30. The boundary condition imposed on the test is horizontal displacement towards ; the backfill without rotation (torsion or rocking) or uplift. ; The modest-Dr specimen (T8.0-1) exhibits nearly elastic-plastic response with negligible strain softening. The peak resistance was ; approximately 700 kips (3114 kN), which corresponds to a passive earth pressure coefficient of Kp=10, and occurred with a wall-soil interface ; friction that is approximately half of the soil friction angle. The high-Dr specimen (T8.0-2) exhibits a strongly strain softening response with a peak ; resistance of approximately 1650 kips (7340 kN) and large-strain (approaching residual) capacity of approximately 1100 kips (4900 kN). These ; capacities correspond to Kp values of 24 and 17 for peak and large-strain conditions, respectively. ; Using shear strength parameter derived from triaxial drained strength testing, log-spiral hyperbolic (LSH) simulations of the backfill response ; are performed that modestly under predict the peak specimen responses. However, the degree of underprediction is modest relative to the substantial ; differences in capacity between specimens T8.0-1 and T8.0-2. Those large variations in capacity are well captured by the analysis, suggesting that ; the LSH method can account for the effects of compaction condition on the wall capacity. The LSH simulations are also able to capture variations in ; specimen response for different wall height. ; We recommend that the height scaling effects in future versions of the SDC be modified to more realistically capture the different trends for ; cohesive and granular backfills. For granular backfill, stiffness and capacity should scale by an exponent n = 1.5-2.0. We also recommend that ; compaction condition be considered in the specification of stiffness and capacity.
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• Format:
  PDF
• Funding:
  59A0655
• Download URL:
  https://rosap.ntl.bts.gov/view/dot/25729/dot_25729_DS1.pdf
• File Type:
  [PDF - 4.60 MB]
• Collection(s):
  US Transportation Collection
• Main Document Checksum:
  urn:sha-512:9e53c614d6687dfc0817a0f71203b5ec302ba9629cbb87c3b4aa0cf27db088887c531e9f5d1f5315e19cd5251921a97b1b51f4d4883fc162f331dd2a27a38d6c