What is the purpose of leveling pad in bridge bearing?

Bridge bearings should be installed to lie horizontally on bridge piers and columns so that it would not induce eccentricity forces on substructure. However, the bridge superstructure requires different longitudinal and transverse level and gradient in order to keep in line with the geometry of the road. As such, it is natural to follow that the superstructure can hardly meet with substructure horizontally so that a leveling pad is introduced at the bottom of the superstructure to join with bridge bearing. Wedge-shaped leveling pad is commonly used for better concrete mobility at the bridge bearings.

This question is taken from book named – A Closer Look at Prevailing Civil Engineering Practice – What, Why and How by Vincent T. H. CHU.