There is increasing demand worldwide for trenchless construction methods, including HDD, for installation of underground utilities. By 2050, the world population will reach 9.7 billion (United Nations, 2019), with 68 per cent of people living in urban environments (United Nations, 2018).

The combined trends of population growth and increased urbanization result in a push for more infrastructure, a lot of it in dense urban areas. This requires increased productivity; that is, to deliver more projects in less time, while maintaining both quality and safety. However, delivering more projects in less time results in higher risk.

Trenchless construction methods inherently involve higher levels of risk relative to traditional open-cut construction. It is important to manage risk appropriately on both open-cut and trenchless construction projects. However, the risks associated with trenchless construction are both more difficult to pinpoint, and less understood. Engineers and contractors can easily do visual inspections to identify problems on open-cut projects. When trenchless methods are used, other options to manage risk are needed.

Fortunately, there is an approach to reducing risk that is often overlooked. Data is a powerful tool that can be used to manage risk effectively, whether it comes from completed projects (historic project data) or projects in progress (current project data). An example of this approach as applied to HDD projects is included below.

Managing Risk in HDD: Analysis of Historic Project Data

An in-depth analysis of risk events – i.e. unplanned events that impacted project schedule – was carried out on more than 100 HDD projects delivered in Western Canada between 2005 and 2009 (Osbak, Bayat and Murray, 2012). The projects were carried out by The Crossing Group, with crossings ranging from 219 m to 1594 m and borehole diameters between 251 mm and 1,524 mm. All unplanned events on each project were identified and categorized using more than 20 distinct event descriptions. The unplanned events included problems attributed to drilling fluid or geotechnical conditions as well as problems with equipment or product pipe, among others (Osbak, Bayat and Murray, 2012). Construction schedules for each project were analyzed to determine the amount of time due to unplanned events. The total time spent on all projects was over 63,000 hours, with approximately 38,000 hours of normal construction activities (see Figure 2).

Figure 2

Analysis of risk involved looking at the number of times each unplanned event occurred (Figure 3). However, addressing the most frequent events may not give the most benefit. Instead, the most attention should be given to events with the highest risk factor, R, which can be determined by multiplying the frequency of occurrence of each event (Focc) by its average impact on the final schedule (Iave) (Osbak, Bayat, and Murray, 2012) as in Equation 1.

R=F_occ×I_ave [1]

Figure 3: Frequency of different risk event types across HDD projects

Figure 3: Frequency of different risk event types across HDD projects. Figure adapted from Osbak, Bayat and Murray (2012) and used with permission.

Once this analysis has been performed, it becomes simple to prioritize risk events according to their impact. For instance, the analysis performed by Osbak, Bayat, and Murray indicates that Tripping to Clean/Gauge Hole, Loss of Circulation, and Wait on Others are the events with the greatest risk factors.

Looking at the impact of unplanned events on final project schedule for the HDD projects analyzed in this work, risk accounted for 15 to 55 per cent of the final project schedule on two-thirds (67 per cent) of the projects (Osbak, Bayat, and Murray, 2012). This gives a corresponding theoretical cost overrun of between approximately 1.2 and 2.2 times the construction budget in the planning phase for two-thirds of projects. While this analysis is based on schedule impacts, a useful comparison is a typical contingency fund set aside on traditional construction projects (e.g. structures or open-cut projects), which ranges from 5 to 10 per cent of the overall budget. It is obvious that for HDD projects, a contingency fund of only 5 to 10 per cent is not adequate to cover the impact of unplanned events on the project schedule.

From this analysis, it was also observed that two-thirds of the problems were somehow linked to drilling fluid and/or annular pressure. Increasingly, industry has realized the importance of drilling fluid management in the overall HDD construction process. Drilling fluid serves several functions in HDD, including transport of cuttings. However, this study highlighted just how important drilling fluid management is, linking it to several other risk events (i.e. high annular pressure and frac-out). This emphasizes the need to continuously monitor annular pressure and understand any changes that occur during each step of the drilling process. Monitoring annular pressure and having reliable downhole data for pressure management are vital to the success of the entire HDD operation.

Figure 4: Average impact of different risk event types of schedule

Figure 4. Average impact of different risk event types of schedule. Figure adapted from Osbak, Bayat and Murray (2012) and used with permission.

While these results are based on the analysis of projects carried out by a single contractor in one region over a specific time frame (2005 to 2009) (Osbak, Bayat, and Murray, 2012), there is a benefit in carrying out similar analyses on a wider scale. Analysis of existing, but undervalued, data can give a clear indication of how best to direct resources, which results in overall process improvements. This approach allows contractors and industry players to mitigate risks when carrying out projects and minimize the impacts of unplanned events on project schedule. It is a solid example of the approach needed to address risk and meet increasing demand. Data-driven analysis acts as a quantitative signpost, allowing efforts and resources to be directed towards mitigating risk events with the greatest potential impact.


There is a lot of data that can be used to enhance risk management and inform best practices in HDD, as well as other trenchless projects. However, this information is sometimes not collected at all, or data that exists is not fully utilized. Identifying and exploiting this undervalued information is an essential strategy to improve trenchless technologies and equip the entire sector as it addresses increasing demand. The importance of trenchless technologies in the emerging economy should not be understated, as population growth and increased urban density drive demand for trenchless construction. Taking another close look at existing data can enhance the ability of the trenchless community to meet future requirements for underground construction.


This article is a shorter version of a paper presented by Dr. Ali Bayat and Manley Osbak at NASTT No-Dig North in 2019. The author would like to thank The Crossing Group (Nisku, Alberta) for providing the HDD data that formed the basis of the risk analysis. and the NSERC Industrial Research Chair program for providing the funding to carry out this research. Thanks also to Lana Gutwin for her assistance in the preparation of this article.


Dr. Ali Bayat is NSERC Associate Industrial Research Chair in Underground Trenchless Construction, director of the Consortium for Engineered Trenchless Technologies (CETT) and professor, Department of Civil and Environmental Engineering at the University of Alberta.

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