Emergency Jacking Tunnel in Compressible Soil-Paper

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After a sanitary sewer collapsed beneath an active Conrail rail line in Jersey City, the Jersey City Municipal Utilities Authority urgently needed to install a replacement without disrupting railway operations. The 180-foot sewer was designed inside a 72-inch steel casing, installed by pilot-guided auger boring between a jacking pit and a receiving pit.<br /><br />The site’s geology posed major risks: 10–20 feet of fill overlay soft, compressible peat and organic soils, with groundwater only about eight feet below ground. These conditions could not reliably support the heavy jacking equipment or maintain the pipe’s alignment. The design therefore combined a drilled-pipe soldier-pile excavation support system, internal bracing, and an 18-inch structural slab supported by rock-socketed micropiles. A concrete thrust block connected the excavation support and foundation so the back wall could resist jacking forces. Micropile load testing and perimeter dewatering supported the design and construction plan.<br /><br />The team selected pilot-guided auger boring because it required relatively little head weight and could navigate uncertain ground. Despite encountering buried boulders, rock, wood, steel, and rebar, the equipment advanced the casing. At one obstruction, workers accessed the tunnel face and removed material manually. The jacking system reached forces of up to 900 kips without movement of the thrust block or back wall.<br /><br />The casing reached the receiving pit with only a slight deviation from target line and grade. The project demonstrated that careful coordination, robust integrated support and foundation design, and a suitable boring method can enable precise pipe installation through weak, waterlogged soils beneath an operating railway.

Keywords

sanitary sewer replacement

Conrail rail line

Jersey City

pilot-guided auger boring

72-inch steel casing

jacking pit

receiving pit

micropiles

soft compressible peat

groundwater dewatering