What is the primary purpose of a stub or perched abutment?

A stub or perched abutment primarily serves to allow for the compacting of the embankment without interference. This design is specifically utilized to create a stable and secure foundation for the bridge while accommodating the necessary ground work surrounding it. By having a stub or perched design, the structural elements can be elevated above the natural ground level, which facilitates the effective placement and compaction of the fill material around the abutment, ensuring a strong, stable support for the bridge superstructure.

The other options relate to aspects that are not the primary function of a stub or perched abutment. For instance, while support for the superstructure is crucial, thermal expansion joints can still be designed into any bridge system regardless of the abutment type. Similarly, extending pedestals into the ground and enhancing the aesthetic design of bridges, while potentially relevant to various bridge designs, does not capture the foundational intent of stub or perched abutments.