Opportunity
The Empire Pipeline, which runs from Buffalo to Syracuse, NY, helps bring much-needed supplies of natural gas from the Marcellus Shale to consumers in the Northeast. The Empire Connector extends the pipeline to Corning, NY, linking it to the Millennium Pipeline.
In 2011, Empire Pipeline (a subsidiary of National Fuel Gas) completed an additional 15-mile (24-kilometer) extension to the Empire Connector. A single 2,643-foot (805-meter) section was needed to cross the Chemung River, Interstate 86, a major railroad, several wetland areas, and a local road. The crossing was complicated by challenging geotechnical conditions.
Solution
Empire Pipeline retained Mott MacDonald to design a trenchless solution for the Chemung River crossing. We developed a geotechnical program to characterize the ground conditions across a wide area, and help identify several possible alignments in the vicinity of the proposed crossing.
This program identified a 110-foot (33-meter) vertical column of coarse-grained soil containing gravel, cobbles, and boulders and extending from the surface to the bedrock shale below. The shale bedrock was selected as the least-risk geotechnical material through which to install the proposed natural gas pipeline.
Mott MacDonald completed a trenchless risk assessment and developed risk mitigation measures to allow for the use of horizontal directional drilling (HDD) methods to install the proposed pipeline. The main risk mitigation measures involved the use of starter casings on each end of the alignment and specifying the use of the “drill and intersect” method to complete the HDD pilot bore.
This method involved individual HDD rigs at each end of the alignment that drilled towards each other, meeting at a defined target depth and location in the middle section of the HDD bore beneath the Chemung River. The use of the drill and intersect method is usually left to installation lengths of 5,000 feet (1.5 kilometers) and higher, but was required due to the necessity of long starter casings.
Pneumatic tools were used to install 330 feet (100 meters) of starter casing on the north end of the alignment. A hybrid direct pipe method was used to install 475 feet (145 meters) of starter casing on the south end of the alignment. Once the HDD installation process was completed and the installed natural gas pipeline was tested, the starter casings were removed from the ground.
Outcome
The use of a microtunnel machine in conjunction with a hydraulic thrust unit allowed for precise steering, a critical aspect for this relatively short “drill and intersect” HDD installation. The crossing avoided damage to several wetlands adjacent to the Chemung River, and avoided disruption to rail and highway traffic.
According to Trenchless Technology magazine, “This difficult and unique HDD project included several cutting-edge trenchless technologies combined with older proven technology in order to successfully complete a short but complex installation. Methods used include: pilot hole intersect, the first-ever North American use of directional microtunneling for installation of large-diameter casing for HDD, pneumatic pipe ramming/auger boring, testing of a new tool developed by Michels for seating large-diameter casing into rock, and rock drilling.”
The magazine quoted Mott MacDonald’s Glenn Duyvestyn: “Individually, no trenchless method could solely overcome the site challenges and risks. Only by combining various trenchless methods were we able to meet the challenges and provide the most cost-effective trenchless solution for the crossing.”
Award
In October 2013, Trenchless Technology magazine announced, “Because of the depths, challenging ground conditions not normally compatible with HDD, environmental considerations, and coupling of innovative trenchless installation techniques, the Empire Connector Project has been named the 2013 Trenchless Technology Project of the Year Winner for New Installation. (Another Mott MacDonald project, the Keswick Effluent Outfall Project, was the runner-up in the same category.)