CSX crews were surfacing mainline track in Baltimore when the tamping equipment struck an object immediately below the ties. Investigation revealed that it was a manhole associated with nearly 6000LF of 36″ water main primarily running immediately below the tracks. The municipality relocated the water line, but was faced with the challenge of abandoning the pipe from just two intermediate points. There were three sections of pipe; 1200LF, 1600LF & 2900LF. Various solutions were floated, including threading sacrificial tubing and grouting on the way out, but none were economical or could guarantee a pipe abandonment below the railroad.
The project designer, OBG, identified cellular concrete as a potential solution to the problem, and reached out to CJGeo to determine feasibility. CJGeo confirmed the appropriateness of cellular concrete and set out to create a grouting plan. Coordination between the utility contractor and slurry provider (the site was too small to set up a batch plant) was crucial to ensure that the runs of pipe were all successfully filled in a single shot each. With train frequencies of 3-4 per hour, if the operation didn’t work and the pipes were only partially filled, there was no opportunity to create intermediate access points to finish grouting a section of pipe.
Based on the required bearing capacity and production requirements, CJGeo proposed 22lb/cuft cellular concrete for the abandonment. With a 25psi break strength at 28 days, the mix provided the required strength, met the CSX utility occupancy standard for abandonment, and maximized expansion in order to ensure the longest run, which required nearly 1000CY of finished product, could be grouting in a single shot.
CJGeo mobilized a 150CY/hour cellular concrete crew to the site and performed the two shorter runs the first week. The project was broken into two different weeks due to the criticality of ensuring the longest run was filled completely without issue. The first two runs allowed CJGeo, the GC, railway flaggers, railway operations and the slurry provider the opportunity to work out any kinks in operations during the lower risk placements.
The following Tuesday, starting at 0600, Chaney Enterprises delivered the first of 24 loads of slurry. Completeness of fill was confirmed by uniform cellular concrete venting out the far end of each placement. Overall, the work was completed in three days. CJGeo generated & pumped a total of 1710 cubic yards of cellular concrete to successfully complete the abandonment.