2013 Project of the Year - New Install Winner
Empire Connector Extension Using HDD, Corning, N.Y.
By Jim Rush Oct 28, 2013
The practice of shale drilling for natural gas extraction has been increasing steadily in the United States as this cost-effective and abundant alternative fuel source is further developed. Of course, the increased production means that new pipelines need to be constructed to move fuel to market.
In the construction of new pipelines, horizontal directional drilling (HDD) has found a niche as the go-to method for road and water crossings. In the case of the Empire Connector Extension project in New York, HDD was used for a series of crossings to install a 24-in. diameter natural gas pipeline between Tioga County, Pa., and Steuben County, N.Y.
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 the New Installation.
Empire Pipeline, a subsidiary of National Fuel Gas, completed construction of a 14.9-mile extension of their Empire Connector natural gas pipeline through the Corning, N.Y., area. The extension was being built to install a 24-in. diameter natural gas transmission pipeline between Tioga County, Pa., to Empire’s existing Corning Metering and Regulating Station in Steuben County, N.Y.
This pipeline will provide transportation services for extensive Marcellus Shale natural gas production along the proposed pipeline corridor. As part of this project, Hatch Mott MacDonald recommended the use of HDD as the preferred trenchless method to the owner for installation of a 2,643-ft, 24-in. diameter natural gas line crossing beneath some major obstacles in a congested area adjacent to a major river that included several critical features:
- The Chemung River
- Interstate 86
- A major Railroad – Conrail
- State Highway 352
- Several wetland areas adjacent to
- the river, and
- A local road
An extensive geotechnical investigation program was completed to help characterize the ground materials, behavior and geotechnical based risks. This program confirmed extensive deposits of coarse grained soils, consisting of large deposits of gravel, cobbles and boulders extending from the ground surface to the depth of shale bedrock, which reached a depth of between 75 to 110 ft below the ground surface at both the entry and exit sides of the installations.
The spatial extent of the coarse-grained deposits was verified during initial site visits where sand and gravel quarries were lined up on either side of the Chemung River for several miles upstream and downstream of the proposed crossing location. The overburden soils typically consisted of 36 to 62 percent gravel (over 40 percent is considered questionable for drilling), 25 to 44 percent sand, and 13 to 21 percent silt/clay. The majority of the gravel encountered was greater than 0.75 in. Cobbles were inferred throughout the soil column, based on the reaction of the drilling process. Coring operations were used to advance through boulders and bedrock materials. The unconfined compressive strength of the shale bedrock ranged from a low of 7,380 psi to a high of 15,110 psi. The rock quality designation ranged from a low of 8 to 25 percent in the weathered section and 60 to 100 percent in un-weathered sections. The majority of the rock quality designation was greater than 60 percent.
Constructability reviews identified the shale bedrock as being the more favorable formation for the HDD installation beneath the coarse grained alluvial soils. Mitigation measures and risk workshops were held with the owner, designer and HDD contractor (Michels) to identify construction risks and develop the most appropriate methods for getting to the shale bedrock formation. The outcome of this workshop was to use proven methods and techniques of installing temporary starter/conductor casings at each side of the crossing through the soils and seated into the bedrock materials at depth. Given the relative long lengths of casing pipe, contingency plans were developed in the event the conductor casing pipes were not able to be removed from the ground following completion of the HDD process.
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 included: pilot hole intersect, the first-ever North American use of directional microtunneling for installation of large-diameter containment 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 main challenge to the project included the extensive deposits of gravels and cobbles overlying the shale bedrock throughout the Chemung River Valley,” said Glenn Duyvestyn, senior associate and principal project manager for Hatch Mott MacDonald. “These materials represented the most challenging risks to any trenchless solution. 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.”
Construction challenges included: maintaining grade while installing conductor casings through the difficult ground formation containing a high percentage of gravel/cobble/boulders; removing the directional microtunnel machine and re-inserting the casing pipe within the microtunnel bore using a pipe thruster; intersecting the two pilot bores; staging and installing product pipe: and removing all conductor casings from the ground following completion of a post-installation pressure test.
This design approach initially called for pneumatic ramming/auger boring methods. Casing pipe diameters were originally selected to allow for telescoping casings in the event difficulties were encountered. Deflection of the casing pipe off line and/or grade was identified as a great concern given the required lengths of the casing pipes needed to reach shale bedrock. The north side of the crossing required a 338-ft long casing pipe on a steep entry angle of 16 degrees. The south side required 475-ft long casing pipe on a steep entry angle of 11 degrees. If the line and grade of these casings differed to any degree, the HDD drilling process would have been significantly impacted.
During the pre-construction planning phase, Michels presented an alternative casing strategy for the south side of the crossing consisting of a combination of Herrenknecht Direct Pipe/microtunnel and pneumatic pipe ramming/auger boring install the large-diameter conductor casing on the south side of the crossing. Upon review of this alternative, Hatch Mott MacDonald recommended an extension of the 60-in. diameter of the initial starter casing to protect a nearby county road during the microtunnel machine extraction process. This extraction process involved advancing the MTBM and 42-in. conductor casing using a pipe thruster through the overburden soils and into the shale bedrock below. The casing pipe and microtunnel machine were extracted from the ground while a thick bentonite mixture was injected to help support the excavated bore. The microtunnel machine was then removed and the casing was reinserted into the excavated bore. Reinsertion was completed without incident for the first 355 ft upon which a pneumatic hammer was used to complete the casing installation.
Utilization of the MTBM in conjunction with the Herrenknecht pipe thruster allowed for more precise steering and placement of the conductor casing providing critical alignment and a maximum target length for intersecting the two pilot bores. Once the casing pipes were installed, drilling from both sides of the crossing commenced with completion of the intersecting pilot bores occurring in the vicinity of the horizontal section of the bore. The pilot bore was then reamed using the north drill rig to pull the hole opener while the second drill rig provided rotation of the entire assembly.
Once the reaming was completed, the product pipe was installed, tested and accepted by the owner. The conductor casings were then removed from the ground using pneumatic tools.
Jim Rush is editor of Trenchless Technology.