substructure

The supporting part of a structure; the foundation.

The earth bank or bed supporting railroad tracks.

A substruction; any under-structure; a foundation.

Same as substruction.

An under structure; a foundation; groundwork.

The supporting part of a structure (either physical or organizational; the foundation); underbuilding.

The earth or gravel that railway sleepers are embedded in.

lowest support of a structure

the basic structure or features of a system or organization