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

Micropiles are small-diameter (less than 300 mm) drilled and grouted piles that are used for bridge rehabilitation and underpinning. When micropiles are installed to strengthen the foundation of an existing bridge, the expansion joints must be designed to accommodate the change in foundation stiffness. Micropile installation for bridge rehabilitation is performed through the existing bridge deck or from the sides of the abutments and piers. The micropiles are drilled through the existing foundation and into the competent bearing stratum. The micropiles transfer the bridge loads to the competent stratum, bypassing the weak or deteriorated original foundation. Foundation stiffness change from micropile installation affects the movement distribution between the expansion joints and the foundation. Before micropile installation, the foundation may be settling, causing the joint gap to change. After micropile installation, the foundation is stabilized, and the joint gap should remain constant. Joint gap adjustment after micropile installation may be required if the foundation settlement has caused the joint gap to deviate significantly from the design value. The joint gap can be adjusted by shimming the edge beams or by installing a new joint with the correct gap setting. Monitoring of expansion joints during and after micropile installation is recommended to track any changes in the joint gap. Displacement sensors at the joint allow the gap to be monitored continuously during the installation. Any unexpected changes in the gap should be investigated to determine the cause. Post-installation inspection of expansion joints after micropile installation must verify that the 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 returned to service.