bed - a foundation of earth or rock supporting a road or railroad track; "the track bed had washed away"

raft foundation - a foundation (usually on soft ground) consisting of an extended layer of reinforced concrete

structure, construction - a thing constructed; a complex construction or entity; "the structure consisted of a series of arches"; "she wore her hair in an amazing construction of whirls and ribbons"

support - supporting structure that holds up or provides a foundation; "the statue stood on a marble support"