STRENGTHENING OF STONE MASONRY ARCH BRIDGES THREE ...

Common Problems
River bed profiles may be determined by poling or by a leadline but it must be bond that
a scour hole produced when the river was in flood may have refilled as the flood
subsided but that the material will not be compacted and will provide relatively poor
support to the foundations.
Fig. 4.3 – Damaged foundation
Underwater inspection is also difficult during periods of fast water flow. Knowledge of
the foundation depth is also essential if there is any possibility of scour occurring.
4.2 Arch Ring
4.2.1 Splitting beneath the spandrel walls
Spandrel walls stiffen the arch ring at its edges. Flexing of the arch ring due to traffic
loads will produce shear stresses in the ring where the relatively flexible part with only
fill above it is stiffened by the spandrel wall, and these stresses may result in a crack.
This type of failure may be assisted by rainwater getting into the structure at the
parapet/surface joint and causing particular damage to the arch ring mortar where the
spandrel wall meets the ring.
The effect of spandrel stiffening is not fully understood at present but it is known that
even when the wall is fully separate from the arch ring, it provides some degree of
support due to friction between the fill and the wall.
Leonardo da Vinci Program 29