Two Case Studies of Trenchless Technologies in the Urban Environment

In 1998, EPCOR undertook an inspection program on the condition of 14 of their underground high voltage transmission lines where they crossed the riverbed of the North Saskatchewan River within the City of Edmonton. Based on the findings of this investigation, it was determined that two of the river crossings were at serious risk of mechanical damage. It was decided that they would be replaced by horizontal directional drilling (HDD) methods, at a sufficient depth into the bedrock below the river bottom to remove any risk of failure due to mechanical damage. This paper examines all phases of the work carried out from project inception to construction of the two crossings, first in the spring of 2003 and then in the dead of winter of 2004. Some of the technical considerations inherent in the design of the HDD installations included geotechnical concerns with potential drilling fluid frac-out and slope stability, as well as heat dissipation rates and operating constraints of the 72 kV oil-filled pipe type high voltage cables. This paper will focus on project constraints imposed by the existing urban (park and residential) locations, community and stakeholder concerns and the regulatory and approval requirements of three levels of government. In addition to the necessary geotechnical investigations, other investigations included addressing potential impacts on the river, vegetation, wildlife, archaeological, noise and construction concerns. An extensive public communications program was completed that included a number of open houses, delivery of construction notices to all surrounding residences, meetings with community league executives and other stakeholder groups. The paper will describe the challenges that the project team faced and how they were overcome and the amount of time and effort that went in to meeting those challenges. The paper will end with a discussion of the costs and time frames required to complete such a project.