Taking Advantage of Pipe-String Buoyancy During Long and Difficult HDD Installations

Abstract

Horizontal Directional Drilling (HDD) is one of the oldest ‘new installation’ trenchless technologies in use today and continues to rapidly grow and develop. HDD contractors are successfully completing ever-longer and evermore-challenging bores when installing water and wastewater pipelines. This is a function of the continual advance in technology, plant and equipment, installation practices, and correct product pipe material selection. The combination of thorough planning, detailed design and continual advance in technology has provided contractors with the tools to reduce pull forces during pull back and increase the scope of the installation method. Pipeline buoyancy mitigation is the key component that can reduce pullback forces for longer installations and eliminate critical collapse concerns for deeper installations. Product-pipe material evaluation, combined with successful water-ballasting of the pipe-string during the pull-back process contributes to a reduction of pipe to borehole friction and thereby lowers pull force. This may result in a smaller outside diameter pipe selection, thinner pipe walls required, smaller HDD rigs and less plant and equipment employed, and all of these may reduce the capital cost of construction to complete some of these very difficult installations. This paper will discuss the merits of ballasting pipe strings during the pull-back process for HDD installations. It will take a close look at the mechanical properties of the most popular modern thermoplastic materials for use in HDD and will review case studies of difficult installations completed in North America and New Zealand with the aid of buoyancy modification. 1.5 - 1

Techniques