Abutment Earth Pressure [PIG]

The Abutment Earth Pressure workflow item applies lateral earth pressure or a live-load surcharge against the back wall (and optionally the footing) of a selected abutment. The object builds a triangular (earth pressure) or uniform (live-load surcharge) surface load on the abutment FE group using an input active earth-pressure coefficient and backfill unit weight, and activates it at the specified construction stage.

General

Abutment: Pick the abutment on which earth pressure is applied. The back-wall geometry, footing, and alignment are pulled from the selected abutment.

Stage: Construction Stage at which the generated surface load becomes active.

Load Type [Earth Pressure/Live Load Surcharge]: Choose the load to generate:

• Earth Pressure (0, default): Produces a triangular pressure distribution that is zero at the top of the back wall, equals K_a * unit weight * back-wall height at the base of the back wall, and (if a footing exists) continues down the footing face to K_a * unit weight * total height.

• Live Load Surcharge (1): Produces a uniform horizontal pressure equal to K_a * unit weight * heel width applied over the back wall and footing. Use this to model the effect of a live-load surcharge on the backfill.

Active Lateral Earth Pressure Coefficient (Ka): Active earth-pressure coefficient used to convert vertical soil pressure into horizontal pressure (K_a). The default value is 0.523599. For a level backfill with no wall friction this can be estimated from (1 - sin(phi)) / (1 + sin(phi)); refer to AASHTO LRFD 3.11.5 for guidance.

Backfill Soil Unit Weight: Unit weight of the retained backfill soil used to compute the vertical effective stress (typical US units pcf, SI kN/m³). The generated load is only produced when this value is greater than zero.

Heel Side Width: Horizontal heel width used only for the Live Load Surcharge case to convert the specified Ka and unit weight into a uniform back-wall pressure. Only visible/editable when Load Type is set to Live Load Surcharge.