News
March 2008 - Nicholson Jet Grouting Supports Sewer Systems Nicholson recently completed unique jet grouting projects for a wastewater pumping station in Queens, NY and a sewer system in Cincinnati, OH. Warnerville Pumping Station The Warnerville Pumping Station in Queens was commissioned by the New York City Department of Environmental Protection as part of the area's new combined sewer overflow system. In early 2007, Nicholson was awarded the contract to install a bottom plug for a 60-foot-diameter shaft. The shaft was constructed by general contractor E.E. Cruz with driven sheet piles. Permeation grouting was originally specified for the shaft's bottom plug, but Nicholson proposed and designed a less expensive and technically superior solution using jet grouting. After the sheet piles were driven and micropiles were installed at the base of the shaft, Nicholson installed 209, 5.5-foot diameter jet grout columns to create a completely watertight seal at the base of the shaft. The fine sands present at the site combined very well with the jet grout to create a uniform end product. The site's high water table presented some challenges for Nicholson. As a result, work platform stability was a constant concern. E.E. Cruz prepared the platform each evening by grading off spoils. Platform stability problems diminished once 25% of the jet grout columns were installed. The high water table also meant the jet grout bottom plug had to withstand 55 feet of water pressure trying to displace it. Even one small leak would have caused major problems during shaft excavation. Columns diameters were estimated from initial tests and then replicated to avoid excessive overlap which might have resulted in the shadowing of the adjacent column. The presence of dedicated onsite engineering staff ensured successful sequencing, layout, quality control, and accurate calibration of mixing controls and drill rig instrumentation. Miamitown Interceptor When complete, the Miamitown Interceptor Sewers Project will provide sewer service to parts of Miamitown and Whitewater Townships in western Ohio. Nicholson was contracted to build an access shaft to serve as the receiving pit for the microtunneling machine constructing the sewer system. Nicholson's work also provided support of excavation for the vortex structure and adjacent manhole. To construct the 29-foot-diameter shaft, Nicholson designed and constructed a series of 59 overlapping jet grout columns that reached a depth of 61 feet. Nicholson also constructed a 20-foot-thick bottom plug with 76 jet grout columns to ensure a watertight seal at the base of the shaft. The jet grout scheme was selected due the extremely congested nature of the site. The shaft is located in the front yard of a residential property. The jet grouting ensured minimal disturbance to the house and other nearby structures. A more traditional shaft construction method, such as sinking a shaft, would have resulted in far more disruption to the neighborhood. To verify that the jet grout columns met the design requirements, Nicholson employed CYLJET® technology, which confirms in situ column diameters using the electrical cylinder method. CYLJET® consists of recording and analyzing the potential differences generated by an induced electric current around a borehole. The electric monitoring field around the hole takes the form of a cylinder 16 to 33 feet in diameter, depending on the electric resistivity of the ground and instrumentation system employed. CYLJET® was developed and patented by E.D.G., a specialist in applied geophysics and a subsidiary of Soletanche Bachy, Nicholson's parent company. Date: March 12, 2008
The Warnerville project site .jpg)
The excavated shaft
The congested Miamitown site 
The excavated jet grout shaft
Contact: Brian O'Gara
Phone: 412-221-4500
Fax: 412-221-3127
Email: bogara@nicholsonconstruction.com