Evaluating ArrowBore—An Engineers Perspective

This paper presents a case history from the engineers perspective of the use of a patented ArrowBore technology for installation of three parallel water lines. Additionally, this paper researches other installations of gravity pipelines by the ArrowBore technology and evaluates suitability for future projects. The ArrowBore technology (also known as close tolerance HDD) is a modification of standard HDD process where vertical sight holes are drilled about every 15 to 50 feet over the alignment to facilitate sighting the pilot bore and to relieve the drilling mud pressure. As the product pipe is pulled into the reamed hole, the drilling mud is displaced up the sight holes and is vactored out of the holes. As the product pipe passes the first sight hole, the path of the drilling mud is effectively shifted to the next sight hole. The case study is for the three water lines installed as temporary pipelines for bypass flow to allow CIPP lining of the larger diameter water transmission lines. The design engineer specified HDD for installation of the three temporary water pipelines. During the submittal review phase, the contractor proposed using the ArrowBore technology. The owner agreed to this innovative technology as a “pilot project”. This paper discusses the ArrowBore process, how concerns raised by the design team during the submittal review were addressed, and how construction using the ArrowBore process progressed. Additional information about other installations will be summarized and we will present our conclusions regarding the benefits and risks of this technology and the applicability of the CTHDD process to other projects.