Chemung River Challenges No Match for HDD

Abstract

Empire Pipeline, a subsidiary of National Fuel Gas, recently completed construction of a 14.9-mile extension of their Empire Connector natural gas pipeline through the Corning, New York area. As part of this project, trenchless methods were evaluated for a single 2,643-foot crossing of the Chemung River, Interstate 86, a major railroad, a State Highway, several wetland areas, and a local road. A geotechnical program was developed to characterize several alignments in the vicinity of the proposed crossing location. These borings indicated a 100-foot vertical column of coarse grained soils, consisting of extensive deposits gravels, cobbles, and boulders extending from the ground surface to shale bedrock beneath. Risk mitigation measures were developed for the coarse grained soils to allow for the use of horizontal directional drilling (HDD) methods to complete the crossing. In the end, a construction methodology involving HDD, microtunneling/direct pipe, and pneumatic pipe ramming/auger boring methods were used to successfully complete the crossing.

This paper summarizes several design and construction challenges associated with the crossing. Design challenges include determining the most appropriate and cost-effective trenchless installation method, mitigating the presence of the thick deposits of coarse grained soils, including a requirement for starter casings on both ends of the alignment, and specifying the use of the drill and intersect method for such a short crossing. Construction challenges included installing the conductor casings, removing the microtunnel machine and  re-inserting the casing pipe within the microtunnel bore, intersecting the two pilot bores, staging and installing the product pipe, and removing all conductor casings from the ground following completion of a post-installation pressure test.