North American Oil & Gas Pipelines

JUN 2018

North American Oil & Gas Pipelines covers the news shaping the business of oil and gas pipeline construction and maintenance in North America, including pipeline installation methods, integrity management innovations and managerial strategies.

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Page 35 of 43

36 North American Oil & Gas Pipelines | JUNE 2 018 Managing risks requires thorough characterization of chal- lenges associated with a particular crossing and proper de- signs to mitigate identified risks and reduce the overall risk profile to an acceptable level. Relying solely on a contractor to overcome design deficiencies presents, in itself, a signifi- cant risk to a successful waterbody crossing. Similarly, apply- ing a specific trenchless method to a crossing without due consideration of the impacts associated with the construc- tion method may increase impacts to local areas and negate the reasons or decisions for undertaking the trenchless cross- ing in the first place. Averting Challenges Specific engineering challenges associated with water- body crossings typically include geotechnical based-risks, environmental considerations, site-specific constraints, ac- cess and workspace considerations, historical land use, and trenchless construction method-specific challenges. These challenges must be addressed during the design phase of the project to enhance the crossing success while avoiding sig- nificant impacts. Geotechnical-based risks are associated with the type, properties and behavior of the encountered geotechnical materials/soils. For shorter crossings, it is recommended that boreholes be completed on or as close as possible to each bank or edge of a crossing feature. Boreholes completed far away from a waterbody crossing due to an inability to access or to mobilize equipment to the crossing location introduce risks associated with unknown geotechnical conditions until the time of construction, when the construction contractor may not be able to effectively manage the encountered geo- technical materials. Larger waterbody crossings can require boreholes completed within the waterway from a barge (see above right) to collect pertinent information associated with the ground conditions and anticipate behaviors. Planning of geotechnical programs must consider the number of boreholes, termination depth, and spacing be- tween boreholes. The termination depth must account for at least the anticipated depth of a trenchless crossing and should collect information at deeper depths in the event unfavorable ground conditions are encountered and the anticipated installation depth is deepened. If additional depth is not completed, the probability of needing to re- turn to the field to collect additional geotechnical informa- tion increases. The results of the geotechnical investigations should be used to verify the selected trenchless method for a cross- ing. If the risk factors are too great to overcome for a spe- cific trenchless methodology, an alternative construction method must be considered. It is not sufficient to complete a geotechnical program just as a "check-the-box" process or push the risks to an HDD contractor. If geotechnical risks are identified, the trenchless design must mitigate the risks to an acceptable level. Environmental considerations include evaluating the impacts of performing the geotechnical program, creation of access roads to the crossing feature, construction of large workspaces for setting up trenchless equipment, and po- tential false right-of-way requirements to fabricate, test and stage the product pipe. Often, the impacts associated with a trenchless construction method are far greater than the impacts associated with a short open-cut crossing with mitigation measures employed to minimize work space requirements across the critical feature while maintaining water flow and minimizing water quality and environmen- tal concerns. Trenchless method specific challenges need to be consid- ered and fully evaluated to determine potential impacts to a Left (top and bottom): Historic photographs showing construction of a pipeline across the Ohio River in 1947. Right: Drilling geotechnical borings from a barge in the Hudson River.

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