Bridge Expansion Joint for Bridges with Expansion Joints in Deck Slabs on Caissons

Caisson foundations for bridges are large-diameter, deep foundations that are constructed by sinking a hollow structure into the ground. The construction of caissons near existing expansion joints requires careful planning to minimize the effects on the joints. Open caisson construction involves sinking a hollow structure into the ground by excavating the soil inside the caisson. The caisson sinks under its own weight as the soil is removed. The construction can cause ground settlement and vibration that can affect adjacent expansion joints. Pneumatic caisson construction involves pressurizing the working chamber at the bottom of the caisson to prevent water and soil from entering. Workers enter the pressurized chamber to excavate the soil. The pressurization can cause ground heave and settlement that can affect adjacent expansion joints. Ground settlement from caisson construction can be minimized by careful excavation and by grouting the annular space between the caisson and the surrounding soil. Ground settlement monitoring is recommended during caisson construction near existing structures. Vibration from caisson construction is typically lower than from pile driving, but can still be significant if blasting is used to break up hard rock. Vibration monitoring is recommended during caisson construction near existing expansion joints. Post-construction inspection of existing expansion joints must verify that the caisson construction has not caused any damage. The inspection should check the joint gap width, the concrete edge beam condition, and the anchor bolt torque. Any damage must be repaired before the bridge is returned to service.