Railway Grade Crossing Repair

Railway Grade Crossing Repair–Foam Jacking, Charlotte, North Carolina

Problem:

Settlement of precast grade crossing slabs on a passenger light rail double track grade crossing adjacent to urban primary road intersection.  Up to 1.0 inch of deflection occurred during train passage, requiring a speed restriction, and individual panels were differentially settled up to 1.5 inches.  Previous repair attempts using cement-based grout had failed.  The grout used for previous repairs had pulverized with dynamic loading and been pumped out of the ballast as a result of the dynamic loading associated with rail traffic.

Three tracks were affected; a both sides of a double track crossing in one location, and a single track of a double track crossing at another location.  All of the precast crossings were constructed of Oldcastle Star Track panels.

Constraints: 

18 hour per day train traffic, heavy vehicular traffic around the clock.  Crossing had to be returned to use by both rail and automobile traffic immediately after repairs were completed, and repairs could not cause rail traffic schedule disruptions.

Solution:

High density polyurethane injection to stabilize and lift slabs.  High density polyurethane foam was chosen for its fast reaction speed to allow for individual adjustment of the panels and minimize chances of disturbing adjacent asphalt pavement.  Since the polyurethane foam used for foam jacking reacts quickly, undesirable lateral spread can be avoided.  This facilitates fine tune lifting to correct differential settlement despite the relatively narrow footprints of the precast panels relative to their weight.

Result:

Concrete Jack lifted and stabilized 214 linear feet of crossing slabs over two nights (11pm to 5am) with immediate vehicular and train traffic outside of work hours.  This grade crossing repair was completed on budget, on schedule, and with much less disruption than associated with mud jacking.