Auger Bores Into The Apple

Edited by Matthew Phair | September 28, 2010

Staten Island homeowners faced a dilemma. The outfall of the sanitary sewer was located in a sewer easement adjacent to six private properties. These properties were bordered by a fenced retaining wall used to contain areas where in-ground and above-ground pools were located in well-manicured yards. Because of the depth of the sewer, the pools were in the influence line of the trench excavation.

The property owners were told they would have to remove their pools to allow the construction of the sewers. Although the city had the right to install the sewers and had given advance notice to the residents to remove their pools, the residents chose not to follow through with the city's instructions. There were considerable risks of potential claims and legal costs as well as additional cost of restoration of walls and fences, and other problems that might arise from vibration and ground settlement.

While DiFazio Industries was discussing sheeting requirements for this section of the 18-inch sanitary sewer, the Icon Group suggested Bohrtec pilot tube guided auger boring, whereby only two pits at each end would be required for a 300-foot stretch of sewer. This low-impact method was ideally suited for that specific section of the project due to the soft clay soil condition, confined working spaces and the tight Line & Grade tolerances required for the gravity sewer installation. Since no open trenches would be required adjacent to the properties, no removal of the pools would be necessary.

The Icon Group, Bohrtec's exclusive distributor for North America, prepared a proposal to use a three-stage auger boring method using Bohrtec's equipment to install 300 feet of 18-inch sanitary sewer. This method was never tried in New York City, but was presented to NYCDDC because of its successes in applications outside the city. The method was approved and the work successfully completed with no impact to property owners.

The Icon Group prepared all site-specific engineering for the application of the Bohrtec pilot tube guided auger boring system. DiFazio Industries also installed on site a one-bay sliderail pit 16 feet by 8 feet by 16 feet deep for the required jacking pit and a one-bay sliderail pit 11 feet wide by 8 feet long by 16 feet deep for the receiving pit. The jacking pipes used were supplied by Mission Clay Products.

Liability was a major factor for the consideration and implementation of the pilot tube auger boring method as opposed to conventional trenching. DiFazio Industries opted for the guided auger boring to avoid risks of potential claims and legal costs. In addition, trucking costs were significantly reduced as a result of using the compact Bohrtec's auger boring equipment.

Overall, the now-complete, $9-million project included the installation of 8,940 linear feet of sanitary sewer, 10 inches through 18 inches in diameter; 5,140 linear feet of storm sewer, 12 inches through 30 inches in diameter; and 4,200 linear feet of water main, 6 inches through 12 inches in diameter.