Define Masonry substructure- underwater inspection of bridge?

In early days, masonry, particularly stone masonry was extensively used for bridge piers and abutments. Typically, bricks and quarried stone were set with lime mortar or Portland cement mortar. Stone masonry structures develop problems at the joints between pieces of stone. Failure of these types of structures usually occurs as a result of wash out of the joints. In addition, increased earth or hydrostatic pressure causes joints to crack and masonry to fall out. Weathering of masonry under constant wave action of water is another cause of deterioration.