Solid backing is actually a major structural component of a stone arch bridge which uses it. One of its advantages is that it provides a more consistent stiffness behind the arch.
Fill-related problems in a stone arch bridge take on several forms, but often result in bulging, sliding, and failure of bridge components. These problems can be addressed.
A mortarless stone arch bridge can be quite strong, as the secret to a successful stone bridge is to keep all the forces in compression as opposed to “gluing” the stones with mortar.
Feathers and wedges are simple-to-use and reliable tools that provide an easy means for obtaining reasonable slabs out of massive, irregularly shaped stones.
Many stone arch bridge feature subtle design features that are tucked away out of sight within the structure, which can greatly complicate rehab and load handling calculations.
Friction is a crucial factor in stone arch bridge stability, and, when the line of thrust is solidly within the arch, holds the arch stones firmly in place.
Bulging walls in the approaches and spandrel walls of a stone arch bridge indicate excessive force against them. This type of problem is fairly simply addressed.
Longitudinal cracking is a common defect on stone arch bridges. While often not overly serious, under the right conditions this cracking can indicate a major problem.
Stone bridges are inherently quite heavy. This can sometimes cause foundational or arch problems, prompting designers to come up with ingenious solutions.
Building an arch that is tapered by making the haunches thicker than the crown is a clever way to make a strong bridge without increasing the “hump.”