Mobilized Shear Strength on the Failure Surface of 2d Belled Anchor Model Piles under Uplift in Cohesionless Soil-Paper

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The study experimentally examined uplift failure around 12 two-dimensional belled-anchor models in dry sand. Models had a 45° bell angle, thickness ratios of approximately 0.28–0.46, and embedment ratios of 3, 4, or 5. Dyed sand layers made it possible to trace the failure surfaces.<br /><br />The observed failure surfaces were nonlinear and were represented by third-degree polynomial equations. The researchers then treated these surfaces as axisymmetric in a horizontal-slice analysis to estimate uplift capacity. The analysis combined the weight of the breakout wedge with mobilized shear resistance along its failure surface, accounting for the direction of anchor movement.<br /><br />Increasing embedment ratio produced larger failure wedges, greater wedge weight and mobilized shear, and higher uplift capacity. At a given embedment ratio, increasing the thickness ratio generally produced smaller wedges and lower wedge weight, mobilized shear, and uplift capacity. Failure surfaces extended to the ground surface and spread farther horizontally with greater embedment.<br /><br />Predicted net ultimate uplift capacities agreed reasonably well with measurements: most errors were within about 10%, although the largest reported error was approximately 14%. The results suggest that traced failure surfaces and slice-based estimates of wedge weight and mobilized shear can help assess the uplift resistance of belled anchors in cohesionless soil. The authors caution that field application should account for actual site soil conditions.

Keywords

uplift failure

belled anchors

dry sand

failure surfaces

embedment ratio

thickness ratio

axisymmetric analysis

breakout wedge

shear resistance

uplift capacity