The Role of Slurry Microtunnelling for Pipeline Installations in Hard Rock Conditions

Abstract Pipe Jacking with Slurry Microtunnel Boring Machines (MTBMs) plays a pivotal role for challenging sections along the main Canadian pipeline routes, through the mountainous areas characterized by high rock strengths. In addition to the well-known pipeline installations with HDD and Direct Pipe, Slurry MTBMs for pipe jacking can be used for safe and precise excavation of small-diameter casing tunnels, also in challenging ground, where alternative methods reach their technical or economic limits. In small-diameter tunnelling through hard rock, the continuous further development of technologies plays a key role to overcome the limitations in rock strength and drive length and to improve performance. The cutting wheel’s tooling composition is one of the critical aspects in rock applications. Tool size and arrangement are determined based on the rock properties, to obtain reasonable rock chip sizes which can be handled by the discharge system. Three main cutting tool types can be considered for MTBMs: disc cutters, TCI cutters or milled tooth cutters. The most common cutting tool remains the disc cutter, which is well known from large diameter hard rock TBMs. Small-diameter hard rock Slurry MTBMs need to have a capability of high jacking forces and both a strong main bearing and cutter bearing. For the latest AVN 800 for hard rock, TCI cutters have been chosen. TCI cutters exert a point load force on the rock, resulting in numerous small chips. Due to the tungsten carbide insert, the TCI cutter is considered especially wear-resistant, which is beneficial for long drives in small diameters, where cutterhead interventions are not possible. In hard rock conditions with high rock strength and/or abrasivity, the applicability of Slurry MTBMs has been especially limited in the non-accessible diameter range in the past. With the latest AVN 800 for hard rock microtunnelling, Herrenknecht has developed a powerful machine concept, enabling drives of up to 200 meters without interventions. Longer drives make microtunnelling a more economic and more environmentally friendly construction method, as the number of shafts can be reduced. New opportunities for clients and consultants in the planning of tunnel routes for different pipeline installations can be considered, making trenchless technologies even more competitive and cost-effective, and improving public acceptance at the same time.