Bridge Expansion Joint for Bridges with Expansion Joints in Deck Slabs on Bored Piles

Bridge decks on bored piles (drilled shafts) require careful consideration of the effects of pile boring on adjacent structures and groundwater. The boring process can cause ground settlement and groundwater drawdown that can affect existing expansion joints and structures. Ground settlement from bored pile installation can occur when the boring process removes soil from the ground, causing the surrounding soil to settle. The settlement depends on the pile diameter, the soil conditions, and the boring method. Ground settlement monitoring is recommended during bored pile installation near existing structures. Groundwater drawdown from bored pile installation can occur when the boring process intersects the groundwater table and the water is pumped out. The drawdown can cause settlement of adjacent structures that are founded on compressible soils. Groundwater monitoring is recommended during bored pile installation in areas with high groundwater tables. Casing installation during bored pile boring can prevent ground settlement and groundwater drawdown by providing a stable bore hole. The casing is installed as the boring progresses and is removed after the concrete is placed. Permanent casing may be required in areas with unstable soils or high groundwater tables. Concrete placement in bored piles must be performed carefully to prevent segregation and voids. The concrete is placed using a tremie pipe that extends to the bottom of the bore hole. The tremie pipe is withdrawn as the concrete level rises to prevent the concrete from falling through water. The concrete must be placed continuously without interruption to prevent cold joints. Post-installation inspection of existing expansion joints must verify that the bored pile installation 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 opened to traffic.