When an unanticipated subsurface condition halted the installation of a wet well through difficult soils at Jackson Redevelopment Corporation’s Dublin Road Pump Station, close cooperation between the owner, general contractor Sambol Construction, Mueser Rutledge Consulting Engineers, and Moretrench was the key to an effective and rapid resolution.
Sambol had constructed three structures at the pump station in Jackson Township, NJ. Construction of the wet well involved an internally-supported sheet pile excavation 32 feet below the ground surface and 28 feet below the static groundwater level. The geologic conditions beneath the site consisted of loose/soft to medium dense/stiff sand, silt, and clay to a depth of 40 feet below ground surface, underlain by medium dense to dense glauconitic silty fine sand. During wet well construction, basal failure, boils, and ground loss occurred. Driven piles were installed to support the wet well structure, but additional ground loss was observed within and outside the sheet pile excavation, followed by 1 to 12 inches of differential settlement of the adjacent pump chamber structure. Post-failure investigations by Mueser Rutledge Consulting Engineers (MRCE) concluded that the ground losses around the pump station structures had compromised the supportive capabilities of the natural subsoils.
Moretrench was contracted by the owner to develop, in conjunction with MRCE, a design-build micropile solution to raise and re-level the settled pump chamber and to provide deep foundation support for the wet well and inlet chamber structures. The use of micropiles was also favored by the team to convey the loading of the structure to deeper, undisturbed soils.
When unexpected failure of the test pile revealed that the subsoils were even more disturbed than previously thought, Moretrench was proactive in quickly adjusting the micropile design to ensure that casing lengths completely bypassed the loosened zones. The 30 piles were successfully installed through the disturbed ground despite adverse construction conditions that included working on decked platforms over water filled tanks.
A synchronized jacking system, reacting against the installed micropiles, was employed to lift the settled structure and return it to its originally planned location. Ten 50-ton capacity hydraulic jacks were connected in parallel to a common manifold and used to jack up the 320,000 lb pump chamber. Over a period of two days, the structure was raised from 1⁄2 to 12 inches and re- leveled to within 1⁄2 inch of its original location. Moretrench’s grouting specialists then injected cement grout, through tube à manchette pipes, beneath the raised structure to re-establish contact with the soils below the pump chamber.