Structures include Bridges, Tunnels, Retaining Walls, and Large Box Culverts. Several studies are done on the load-bearing capability of bridges, and techniques to inspect structures. Eastern Federal Lands (EFL) Bridge Inspection Program is a leader in the area of structure inspection. EFL provides a steady source of feedback to the transportation community on the type of instruments needed by bridge inspectors all over the country. A few articles on the subject and also on the application of stone walls.