In 2011, researchers at Arizona State University completed a survey of pilot tube microtunneling (PTMT) contractors across North America. The survey was developed in consultation with equipment manufacturers, industry consultants and contractors working with the technology. The intent of the survey was to fill an existing knowledge gap related to the business side of the PTMT industry. While the technology’s applications, capabilities and limitations have been well documented in cases studies, there was little documented literature available on the industry trends, business practices and contractor perspectives on the technology.
Arizona State University contacted approximately 100 contractors via phone, e- mail, and mail and received a total 22 responses from active PTMT contractors. It was found that while many of the contractors contacted indicated they provided PTMT as a service, many of them had not done more than a few trial or demonstration projects. While this response rate was not as high as was hoped, it still provided a good representative sampling of contractors from across the continent. A total of 19 responses were obtained from contractors in the United States, with the other two from Canada.
In total, these 22 contractors completed 5,770 trenchless installation projects (auger boring, horizontal directional drilling (HDD), microtunneling, pipe jacking, pipe ramming and PTMT) in the five years between 2006 and 2010. Of this total, PTMT accounted for 450 projects, or 7.8 percent of the total number of projects undertaken by the respondents. Only one of the contractors indicated he/she solely undertook PTMT projects, with the majority offering PTMT as a complementary trenchless installation method. It was found that the majority of PTMT contractors had been traditional auger boring (80 percent of the respondents) or pipe jacking (70 percent of the respondents) contractors. Several contractors also indicated that they have just started using PTMT within the last three years.
Trends in Utilization
Some significant trends were observed that gauged the health of the trenchless industry as a whole between 2006 and 2010. Figure 1 summarizes the total number of projects undertaken by the survey respondents broken up by methodology. It can be seen that the total number of projects undertaken by these contractors had decreased from a high of 1,328 projects in 2007 to a low of 899 in 2010. This equates to a 33 percent decline in the total number of projects undertaken by the respondents and reflects the prevalent market conditions at that time. While auger boring and pipe jacking saw a decrease of 40 percent and 50 percent in utilization, respectively, by the respondents between 2007 and 2010, PTMT witnessed a 56 percent increase in utilization over that same time period. However, PTMT still only represented 12 percent of the total projects completed by the contractors, with auger boring at 50 percent and horizontal directional drilling at 21 percent making up the majority of installations completed in 2010.
It was found that PTMT is commonly used in conjunction with other trenchless installation methods. The three main hybrid versions of PTMT are: PTMT-auger boring, PTMT-horizontal directional drilling and PTMT-pipe ramming. The idea behind such hybrid methods is to establish an accurate alignment using PTMT’s guided pilot boring followed by product pipe installations by the other technology. Contractors are able to leverage the best of both the technologies in the hybrid system through such methods. PTMT-auger boring is the most widely used method among all the hybrids. Eight five percent of the contractors reported that they had used PTMT in conjunction with auger boring. Continuous plastic pipe can be installed using the PTMT-HDD hybrid method; used by 25 percent of the respondents. Thirty percent of the contractors indicated that they had utilized PTMT in conjunction with pipe ramming.
The survey looked to identify factors that affect the productivity of PTMT projects. The responses provided by the contractors were reviewed and categorized by common factors. Figure 2 summarizes the factors and percent of contractors that indicated each factor affected the productivity of a PTMT installation. Ground conditions, including soil type and groundwater table, received the highest rating, with 72 percent of the contractors reporting it as a major factor. Many did not perceive installation depth, as a major factor as the technology, like many of its counterpart trenchless methods, is capable of working at great depths if the ground conditions permit.
The contractors were asked to provide the longest length they had installed in a single drive with pipes of different materials. Fifty percent of the contractors surveyed reported using vitrified clay pipe on their projects. It was observed that 70 percent of the contractors that had used PTMT with VCP pipe recorded their longest drive lengths above 300 ft. Steel pipe was used by 80 percent of the contractors on at least one of their projects. 70 percent of the contractors that used steel pipe recorded their longest drives above 400 ft. The longest drive length among the surveyed projects was 550 ft in which a contractor used steel pipe. Only two of the contractors reported installing concrete pipes with PTMT. The longest drive length, as reported by one contractor, using concrete pipes was 500 ft. It is interesting to note that a drive length of 400 ft had been achieved with HDPE pipe using the hybrid PTMT-horizontal directional drill method.
The survey also asked the contractors to rate risks associated with certain factors and conditions affecting PTMT installations. Table 1 summarizes the results; the rankings were on a scale between 1 and 10 with 10 being the highest level of risk. Survey results indicated that the risk associated with damaging the product pipe and adjacent utilities during an installation had the lowest risk rankings. Approximately, 82 percent of the contractors perceived the damaging of the product pipe as a low risk with an overall risk ranking of 2.2. The highest risks were associated with ground conditions. Sixty eight percent of the contractors indicated clay and silty soils were low risk with a risk ranking of 2.7, while sand and gravel had a much higher risk with a ranking of 6.0, and cobbles and boulders had the highest risk ranking with a score of 9.5, with 91 percent of the contractors indicating it was high risk. While the technology is well applicable in medium to dense sands above the water table, the applicability is marginal in very loose to loose sands above the water table and medium to dense sands below the water table.
The pilot tube microtunneling method while relatively new to North America, has seen an increase in utilization between 2006 and 2010, while more traditional methods of trenchless installation have seen a minor decrease in utilization over the same time. This technology is ideal for the installation of pipe on tight line and grade for installation lengths generally used between manholes in a municipal setting. As the need to replace buried pipe infrastructure in urban areas increase, it is expected that pilot tube microtunneling will see an increase in utilization due to its low impact and small footprint of operation.
The authors would like to express their gratitude and appreciation to Jeff Boschert with the National Clay Pipe Institute for his guidance and assistance in developing the survey, providing contact information and educating us in the art and science of pilot tube microtunneling.
The authors also want to express thanks to the following contractors for their participation in the survey: Aaron Enterprises Inc., York, Pa.; Armadillo Underground Inc., Salem, Ore.; B Trenchless, Henderson, Colo.; Blevins Road Boring, Hudson, Fla.; Bore Master, Inc., Pewaukee, Wis.; Bradshaw Construction Corp., Elliot City, Md.; Brannan Construction Co., Denver; Calgary Tunneling, Calgary, AB, Canada; Claude H. Nix. Construction Co. Inc., Ogden, Utah; Frank Coluccio Construction, Seattle; Kamloops Augering & Boring Ltd., Kamloops, BC, Canada; Magnum Tunneling & Boring, LLC., Houston; Midwest Mole Inc., Indianapolis, IN; North Core, Fargo, N.D.; Pacific Boring Inc., Caruthers, Calif.; Riley Contracting Inc., Norwalk, Ohio; Roddie Inc., Morgan Hill, Calif.; Specialized Services Co., Phoenix; Super Excavators Inc., Menomonee Falls, Wis.; T&D Trenchless, Murrieta, Calif.; and Wayne Arnold Road Boring Co., Smackover, Ark.
Dr. Jason S. Lueke, Ph.D., PEng is an assistant professor at Arizona State University, Del E. Webb School of Construction. Vamseedhar Gottipati, M.S., is BIM scheduler for Enclos Corp, Eagan, Minn.