ANS:E - all the above.

The design of the heel slab of a retaining wall is based on various factors that contribute to the maximum bending moment experienced by the slab. These factors include:

1. Its own weight: The weight of the heel slab itself contributes to the bending moment experienced by the slab. The self-weight of the slab must be considered in the design to ensure that it can resist the resulting bending stresses.
2. Weight of the soil above it: The soil retained by the retaining wall exerts pressure on the heel slab, creating bending moments. The weight of the soil above the heel slab contributes significantly to the bending moment experienced by the slab, especially in taller retaining walls or where the soil is dense.
3. Load of the surcharge, if any: Surcharge loads such as additional backfill, structures, or traffic loads placed on top of the retained soil also contribute to the bending moment experienced by the heel slab. These additional loads must be considered in the design to ensure that the slab can resist the resulting bending stresses.
4. Upward soil reaction: The reaction forces exerted by the soil against the heel slab also influence the bending moment experienced by the slab. These reaction forces vary depending on factors such as soil type, soil properties, and wall geometry.