Development of V-H Yield Envelops of Pile Group Supported Bridges Subjected to Scour-Paper

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The study evaluates the combined vertical–horizontal (V–H) bearing capacity of bridge pile groups under local scour. A three-dimensional finite-element model of a 3 × 3 pile group in dense sand was developed in Abaqus. Piles and the pile cap were modelled as elastic, while the soil was represented using the Mohr–Coulomb model. Scour depth was estimated using the HEC-18 method, and V–H yield envelopes were generated for conditions with and without scour.<br /><br />The analysis examined pile length-to-diameter (L/D) and spacing-to-diameter (S/D) ratios, as well as flow angle, velocity, and depth. The resulting failure envelopes were nonlinear and could be approximated by parabolic curves. Without scour, horizontal capacity generally increased with pile length and spacing. Under combined loading, horizontal capacity initially tended to increase as vertical load rose, but could decline at higher vertical loads.<br /><br />Scour reduced the pile group’s supported length and the soil resistance around the piles, shifting failure envelopes downward and reducing capacity. Greater scour depths produced larger differences between envelopes, with the greatest effect associated with changing the flow angle from 0° to 30°. The influence of flow velocity was also notable, while flow depth had a smaller effect among the parameters considered. The effects of scour were more pronounced for longer piles and tighter pile spacing in the cases studied.<br /><br />The authors conclude that structure-specific V–H envelopes can help identify safe combinations of vertical and horizontal loads without repeating a separate capacity analysis for every load combination.

Keywords

bridge pile groups

vertical-horizontal bearing capacity

local scour

finite-element model

Abaqus

Mohr-Coulomb model

HEC-18 method

failure envelopes

pile spacing ratio

flow angle