Horizontal Directional Drilling Using Ductile Iron Pipe — A Successful Paradigm Shift

The Canyon Regional Water Authority, New Braunfels, Texas, planned for the construction of a major system expansion that included a combination of 35,242 feet (10,742m) of 24 inch (610mm) and 41,625 feet (12,687m) of 30 inch (762mm) ductile iron pipe. Along the planned route there were four (4) sections designed for installation using horizontal directional drilling (HDD). The originally designed HDD installations required transitions from ductile iron pipe to high-density polyethylene (HDPE), the perceived standard piping material for HDD. Having identified this material paradigm within the trenchless industry, the successful bidding contractor approached the Engineer to request a material change for the HDD portions of the new transmission system. Informed about the suitability of ductile iron pipe for trenchless installation, a submittal was initiated which proposed that the HDPE pipe be replaced with flexible restrained joint ductile iron pipe for the HDD portions of the project. This requested change was thoroughly evaluated by the Owner and Engineer, whose affirmative decisions to proceed started the momentum of this paradigm shift. This paper will discuss the process by which the material change was evaluated from an engineering perspective, and from the perspective of the installing contractors, and the constructibility issues with installing ductile iron pipe by HDD.