NC Tub Crossing Repair
Passenger light rail, urban street
The 8′ long panels of tub style grade crossing settled. As a result, a speed restriction was placed on the crossing, which affected passenger schedules. Three panels were affected, and the belly in the slabs was approximately 2 inches. Slight deflection with heavy truck traffic was noted, and significant deflection with rail traffic was present.
The repair had to be completed in just a few hours, to avoid disruption to rail traffic. The repair had to allow for immediate resumption of rail traffic, and tolerate tamping of the adjacent truck during the repair. Additionally, the tub crossing repair had to be done in a manor which did not disturb the adjacent asphalt pavement.
High density geotechnical polyurethane grouting to stabilize and lift the affected modular grade crossing panels. Geotechnical polyurethane grouting is far superior to mudjacking, in that the process is faster, and can more easily ensure a complete filling of voids under the crossing panels. Lifting precision of less than 0.1 inches is standard.
To repair tub style crossings with polyurethane grouting, 5/8″ holes are drilled through the panels. Mechanical packers are inserted into the drilled holes, which are then used for injecting the polyurethane grout. The polyurethane grout is injected as a liquid, and then expands in the space under the crossing tubs. As it expands, the polyurethane grout fills any voids below the panels. If lifting is required, additional injection of grout is done after voids are filled.
Unlike mudjacking, polyurethane grouting tolerates rail traffic during the repair process. The material cures to 95% of ultimate strength in less than 15 minutes.
CJGeo modular grade crossing repair crew filled the voids and corrected settlement in a few hours. During the tub crossing repair, tamping was done by the rail system to address settlement of the adjacent track.