Direct Steerable Pipe Thrusting (DSPT) is relatively new in North America,
with approximately 165 completed installations worldwide since the first
installation in 2007 (Herrenknecht).
DSPT refers to a pipeline installation technique where a Microtunnelling machine is propelled by steel pipe strings by the use of a thruster to achieve curvilinear alignments, long drive lengths, avoid the use of deep shafts, and minimise the potential of hydrofracture, which is typically the driving design factor behind HDD designs. The
method was marketed by Herrenknecht Corporation which introduced Direct Pipe®
to the trenchless industry. Of the 165 installations completed to date, 58 have been
completed in Canada, the United States and Mexico combined. The use of DSPT is now
being considered on many municipal projects as an alternative to horizontal directional
drilling (HDD) and microtunnelling.
The vast majority of projects in North America have been for the energy industry with
only 4 of the 58 projects (just under 7%) constructed for municipalities. As such, data
from the installation is often not shared or easy to obtain. As such, information on
project challenges, solutions, and the advancement of the technology are not widely
published due to the confidentially that is required by Energy Companies.
In addition, many contractors will not share the details of specific projects and
challenges, as they try to maintain competitive advantage. As this method transitions
into the municipal market, there is little understanding and some confusion in the
industry regarding the capabilities of DSPT, what parameters influence the success
of the method, and why one would specify DSPT over the use of either HDD or
Microtunnelling.
Understanding the differences between the three methods (HDD
versus Microtunnelling versus DSPT) and the appropriate application for each is critical
to ensure that the method is used appropriately and successfully on projects. There are
a number of important technical topics that require further research and evaluation to
develop a full understanding of the DSPT method such as:
• Inadvertent Returns and the reduction of hydrofracture potential. Inadvertent returns
are well understood in the HDD industry, and the engineering guidelines available
to assess the potential for inadvertent returns has been studied and used for over
20 years. However, the potential for inadvertent returns is not well understood with
DSPT. The mechanisms that govern inadvertent return potential on HDD projects
are very different than those that exist in DSPT applications. Understanding why
inadvertent returns occur in HDD and do not occur in DSPT is a topic that must be
understood to allow appropriate specification of the method.
• Understanding properties for drilling mud (HDD), slurry (microtunnelling), and lubrication (both microtunnelling and DSPT), and how they impact each of these technologies
differently.
• Development of thrust loads and how to estimate thrust loading for a DSPT installation. It is important to understand the frictional loading that develops during DSPT and how it is different than the pull loads that develop during HDD installation. it is equally important is to evaluate how jacking loads are developed on microtunnels and what differs between a standard microtunnelling jacking force evaluation and one for DSPT.
In the upcoming Summer edition of the NASTT magazine, Trenchless North America, Morty’s Technical Academy will address the DSPT method and the current state of practice in North America. It will also address key features that should be evaluated when determining whether a project is well suited to DSPT, as opposed to HDD or microtunnelling. Inadvertent returns and thrust loading will also be addressed in detail as well as drilling fluid and lubrication properties.
