Installation of underground infrastructure has become more challenging in today's sprawling urban centres. For many types of utility and service, the need to dig under existing roads, buildings and other obstructions has brought a growing interest in horizontal directional drilling.
North America is seeing increased utilization and acceptance of HDD installation methods across all applications, from mini-rig to maxi-rig jobs, according to Richard Levings, American Augers director of product management. That growth is expected to continue this year.
Kevin Conry, senior marketing manager with Toro, agrees. "From natural gas pipelines to wind and solar conduits, telecommunications, DSL and fibre optic installations, utility contractors in Canada have realized the inherent benefits of directional drills compared to excavating or trenching."
"With oil and gas in the shadows right now, large telecoms are putting in miles and miles of fibre network," noted Lee Schroeder, sales manager with Vermeer.
"This small duct work is really driving small- to medium-size machine sales, such as the Vermeer D8x12 through D23x30 S3 Navigator horizontal directional drills. These smaller footprint machines are outfitted with the right power to get through tough jobs in tight urban spaces."
Large HDD units saw a slowdown three years ago in conjunction with a downturn in Canada's energy market. Chris Gambrell, Canadian regional sales manager for Ditch Witch, said that with the oil and gas sector's improvements through recent months, larger HDD units are starting to move once again. "Although the market has not returned to the same level it was five years ago, it continues to increase. In addition, the demand for smaller-sized HDD units (10,000- to 20,000-pound drill class) is also increasing. This trend is being driven by an influx of fibre installation projects across Canada.
Levings at American Augers commented on another aspect of HDD utilization. "There are scenarios in which excavating or trenching is simply cost prohibitive, and the investment in equipment and labour to rehabilitate an installation area would bore into the bottom line of the utility contractor's operation. Furthermore, there are other installation sites that require minimal disruption, which make horizontal directional drills an attractive choice compared to excavators and trenchers."
New technology improves productivity
With the steady growth of underground utility installation, manufacturers have invested in developing their HDD product lines. It's a simple process. Utility contractors know what they want &#; technical advances that help improve their productivity.
In terms of controls, newer machines are transitioning to digitally controlled systems, according to Levings.
"This allows the use of higher performing hydraulic components that offer better efficiency and increased productivity. This also improves the operator interface and increases the available information to make better drilling decisions," he said. "Remote monitoring is now commonplace and allows planned maintenance and remote diagnostics."
Advancements on Toro drills have focused on intuitive controls that allow operators of all skill levels to effectively control the rig. Toro's solution is the new TDOS-1 with SmartTouch drill operating system.
"TDOS-1 with SmartTouch streamlines pipe handling by allowing the operator to use the cam rocker switch to advance through the pipe handling process," Conry explained. "Each push of the switch corresponds to a sequence of pipe handling functions. This makes the pipe handling process easy to learn, improving the operating experience for new operators. In addition, the TDOS-1 with SmartTouch software gives the drill operator the benefit of a more visually appealing and intuitive interface for accessing functions and information on the display.
"Features include the ability to select single or dual joystick mode on the fly, as well as easy-to-use torque, thrust and tool rotation selection limits for quick adjustments to match bore requirements. Display contrast and day/night mode adjustments also allow users to make changes as light conditions fluctuate."
All-Terrain (AT) technology has been a focus for Ditch Witch machines, providing operators additional improvements when it comes to operations on remote and difficult jobsites. In addition, the AT system includes an innovative way of driving the drill bit compared to conventional mud motors.
"At the core of the AT system is dual-pipe technology, which has an inner drive shaft that reaches back to the drill so it can physically control exactly how much horsepower is sent downhole," said Seth Matthesen, Ditch Witch HDD category manager. "The switch from mud motors to AT technology provides operators with a more efficient power option. In comparison to the 50 percent of power sent downhole with mud motors, 95 percent or more of the drill's inner drive power is successfully transferred downhole using AT systems."
Matthesen pointed to the Ditch Witch AT40 All Terrain drill as an example of the AT system and its operation. A 160-gross-hp engine provides operators 20 percent more horsepower in a smaller footprint over competitive 15-foot drill-pipe models in its class, he stated. The unit also minimizes pipe-entry distance, providing operators increased drill pipe support as it enters the ground.
"New HDD machine models produced today utilize the latest engine emissions equipment. With these emissions requirements, machines have typically gotten heavier," Schroeder noted. "Because of weight and footprint increases, we have seen a trend towards smaller drill models doing the work that larger rigs once completed."
He also said that Vermeer has focussed on telematics, such as Vermeer Fleet and Vermeer Fleet +Edge HDD, which have become more prominent and offer many benefits, such as GPS locations, maintenance schedules, diagnostics, performance data and more.
Automation is more of a draw on smaller rigs such as mini-class drills, and will likely not be found at the same level on larger machines, Levings said. That technology and other electronic features are only practical when they offer operators a feasible solution to an actual problem they face on the job, such as increased operational efficiency, greater productivity, or compliance with strict personnel and environmental safety requirements.
"If the new features do not offer a solution truly beneficial to the operators, they just add cost and complexity," Levings said.
"Take rod handling systems as an example. Automated pipe handling is a much more complex feat for larger rigs than it is for the mini-HDD machines. For smaller machines using shorter drill pipe of consistent dimensions and pipe magazines, automated pipe handling is a huge advantage. Automating a small-capacity pipe loader for larger rigs using Range I and II pipe that varies as much as a foot in length from one pipe to another is not easy to achieve, nor as beneficial. We may see auto-pipe handling for the larger rigs eventually, but it's not feasible at this point."
Productivity extends to the speed at which a machine can be deployed and operated, and Toro has incorporated a number of features into its new DD and DD HDD units, Conry related. For example, dual stabilizers on each side of the unit can be independently adjusted to quickly and easily stabilize the unit on uneven ground.
"Fast connection and breakout speed is also a key consideration when it comes to productivity &#; and for longer boring applications, contractors will want to select a unit that offers open-top vice wrenches that provide the operator clear visibility to the tool joint and rods," Conry said.
"Additionally, directional drills are now more powerful than ever before. Toro is proud to offer 2,600 foot-pounds of rotational torque and 22,000 pounds of thrust and pullback on the new DD, while the DD provides 5,000 foot-pounds of rotational torque and 40,000 pounds of thrust and pullback."
For some HDD operators, the development of guidance systems that help ensure precision and tie in with software applications has aided them on jobsites.
One example is how DCI guidance systems and Vermeer drills and technology have developed over the last few years, Schroeder noted.
"With the development of the DCI Falcon [HDD guidance] technology, contractors are able to get real-time data and accuracy. Combined with on-rig bore planning tools (Vermeer BoreAssist), contractors can overlay their real-time data with DCI LWD Live (Log While Drilling) application, allowing them to follow a rod-by-rod plan. That integration is possible due to the rod count feature on our machines to track how many rods contractors are using in a bore, which is tied to the Vermeer drill's software," he said.
Considerations for buyers of HDDs
When it comes to buying an HDD rig, there are a number of recommendations.
Uptime on jobsites keeps projects on time and lends itself to better contractor margins, said Levings, from American Augers. His advice: "Buy units with proven track records of uptime."
He also advised that contractors should choose units sized for the job. "Undersized HDD systems often rob you of profits because of the extra time and effort it takes to complete a project and increase the risk of project failure. Oversized systems usually drive up operating and mobilization costs while struggling to meet the modern jobsite footprint requirements."
Toro's Conry agreed that properly sizing the HDD rig to the application is important, and it's a challenge that should be discussed between the contractor and equipment dealer to determine the best solution for each project.
Machines handle a variety of situations and in many cases have multiple operators. Newer models offer the ability to configure the controls to the style of system your operator has learned and experienced, regardless of brand, Levings said.
"Ensure the supplier has the type of support network that fits you," he concluded. "Construction equipment will experience unexpected issues. Having a network that minimizes the negative effects of these issues is paramount to being successful. [American Augers is] committed to our customer's success with our rigs. Our North American network of authorized dealers and OEM-certified technicians ensures our Canadian customers are up and running no matter where their jobs take them."
Schroeder from Vermeer advised that there are three main things, when looking to buy, that can provide the contractor with a good place to start. First, local support from the equipment dealer &#; will the dealer be available to assist with after-sale support, including parts, service, field support and training? Second, keep in mind machine features that help ensure efficient jobsite performance or productivity. Finally, residual market value &#; will the machine hold value?
"Operational awareness paired with a comfortable workstation can boost ROI on a jobsite," Ditch Witch's Matthesen said. The former is provided by LED screens which improve visibility into machine functions and diagnostics, he added. "Many machines have also integrated tracker information into the drill display to increase productivity and enhance visibility of all jobsite functions beyond drill operation."
"When it comes to quality, selecting a reliable machine is really a no-brainer for contractors. Equipment working in tough conditions, like those utility contractors experience every day, needs to be rugged and durable. Parts availability, field service and on-site troubleshooting and drill operator training are all things to consider when making an equipment/dealer selection, as even just a few hours of equipment downtime can seriously impact the profitability of a job.
"Toro is in continuous contact with dealer and end-user contacts to help develop solutions that can help the contractor out in the field," Conry emphasized. "Some of these latest advancements include enhanced pipe-handling options, available through Toro's SmartTouch system. When it comes to selecting equipment, contractors may want to work with their dealers to determine which productivity-focused features are most important for their specific application, and use them as a resource to figure out which brand and model are best suited for their operational needs.
"A few of the main considerations are the general size and scope of the project, the total length of the typical run, the typical outer diameter of the pipe to run, materials and ground conditions, and environmental factors like traffic, existing structures or tight areas. Contractors can and should work with their equipment dealers to make a decision that is the ideal solution for their specific needs. Contractors can also contact HDD drill manufacturers directly to help answer questions about rightsizing the rig to the application."
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Horizontal Directional Drilling (HDD) process begins with boring a small, horizontal hole (pilot hole) under the crossing obstacle (e.g. a highway) with a continuous string of steel drill rod. When the bore head and rod emerge on the opposite side of the crossing, a special cutter, called a back reamer, is attached and pulled back through the pilot hole.
The reamer bores out the pilot hole so that the pipe can be pulled through. The pipe is usually pulled through from the side of the crossing opposite the drill rig.
Pilot hole reaming is the key to a successful directional drilling project. It is as important to an HDD pipeline as backfill placement is to an open-cut pipeline. Properly trained crews can make the difference between a successful and an unsuccessful drilling program for a utility.
Several institutions provide operator training programs, one of which is University of Texas at Arlington Center for Underground Infrastructure Research and Education (CUIRE). Drilling the pilot hole establishes the path of the drill rod (&#;drill-path&#;) and subsequently the location of the PE pipe.
Typically, the bore-head is tracked electronically so as to guide the hole to a pre-designed configuration. One of the key considerations in the design of the drill-path is creating as large a radius of curvature as possible within the limits of the right-of-way, thus minimizing curvature.
Curvature induces bending stresses and increases the pullback load due to the capstan effect. The capstan effect is the increase in frictional drag when pulling the pipe around a curve due to a component of the pulling force acting normal to the curvature.
Higher tensile stresses reduce the pipe&#;s collapse resistance. The drill-path normally has curvature along its vertical profile. Curvature requirements are dependent on site geometry (crossing length, required depth to provide safe cover, staging site location, etc.)
But, the degree of curvature is limited by the bending radius of the drill rod and the pipe. More often, the permitted bending radius of the drill rod controls the curvature and thus significant bending stresses do not occur in the pipe.
The designer should minimize the number of curves and maximize their radii of curvature in the right-of-way by carefully choosing the entry and exit points. The driller should also attempt to minimize extraneous curvature due to undulations (dog-legs) from frequent overcorrecting alignment or from differences in the soil strata or cobbles.
The REAMING operation consists of using an appropriate tool to open the pilot hole to a slightly larger diameter than the carrier pipeline. The percentage oversize depends on many variables including soil types, soil stability, depth, drilling mud, borehole hydrostatic pressure, etc.
Normal over-sizing may be from 1.2 to 1.5 times the diameter of the carrier pipe. While the over-sizing is necessary for insertion, it means that the inserted pipe will have to sustain vertical earth pressures without significant side support from the surrounding soil.
Prior to pullback, a final reaming pass is normally made using the same sized reamer as will be used when the pipe is pulled back (swab pass). The swab pass cleans the borehole, removes remaining fine gravels or clay clumps and can compact the borehole walls.
Usually a &#;drilling mud&#; such as fluid bentonite clay is injected into the bore during cutting and reaming to stabilize the hole and remove soil cuttings. Drilling mud can be made from clay or polymers. The primary clay for drilling mud is sodium montmorillonite (bentonite).
Properly ground and refined bentonite is added to fresh water to produce a &#;mud.&#; The mud reduces drilling torque, and gives stability and support to the bored hole.
The fluid must have sufficient gel strength to keep cuttings suspended for transport, to form a filter cake on the borehole wall that contains the water within the drilling fluid, and to provide lubrication between the pipe and the borehole on pullback. Drilling fluids are designed to match the soil and cutter.
They are monitored throughout the process to make sure the bore stays open, pumps are not overworked, and fluid circulation throughout the borehole is maintained. Loss of circulation could cause a locking up and possibly overstressing of the pipe during pullback.
Drilling muds are thixotropic and thus thicken when left undisturbed after pullback. However, unless cementitious agents are added, the thickened mud is no stiffer than very soft clay. Drilling mud provides little to no soil side-support for the pipe.
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The pullback operation involves pulling the entire pipeline length in one segment (usually) back through the drilling mud along the reamed-hole pathway. Proper pipe handling, cradling, bending minimization, surface inspection, and fusion welding procedures need to be followed.
Axial tension force readings, constant insertion velocity, mud flow circulation/exit rates, and footage length installed should be recorded. The pullback speed ranges usually between 1 to 2 feet per minute.
The Industry distinguishes between mini-HDD and conventional HDD, which is sometimes referred to as maxi-HDD. Mini-HDD rigs can typically handle pipes up to 10&#; or 12&#; diameter and are used primarily for utility construction in urban areas, whereas HDD rigs are typically capable of handling pipes as large as 48&#;diamter.
These machines have significantly larger pullback forces ranging up to several hundred thousand pounds.
The designer will achieve the most efficient design for an application by consulting with an experienced contractor and a qualified engineer. Here are some general considerations that may help particularly in regard to site location for PE pipes:
Safety is a primary consideration for every directionally drilled project. While this chapter does not cover safety, there are several manuals that discuss safety including the manufacturer&#;s Operator&#;s Manual for the drilling rig and the Equipment Manufacturer&#;s Institute (EMI) Safety Manual: Directional Drilling Tracking Equipment.
Before any serious thought is given to the pipe design or installation, the designer will normally conduct a comprehensive geotechnical study to identify soil formations at the potential bore sites. The purpose of the investigation is not only to determine if directional drilling is feasible, but to establish the most efficient way to accomplish it.
With this information the best crossing route can be determined, drilling tools and procedures selected, and the pipe designed. The extent of the geotechnical investigation often depends on the pipe diameter, bore length and the nature of the crossing.
Refer to ASTM F, Guide for Use of Maxi-Horizontal Directional Drilling for Placement of Polyethylene Pipe or Conduit Under Obstacles, Including River Crossings and ASCE MOP 108, Pipeline Design for Installation by Horizontal Directional Drilling for additional information.
During the survey, the geotechnical consultant will identify a number of relevant items including the following:
(Supplemental geotechnical data may be obtained from existing records, e.g. recent nearby bridge constructions, other pipeline/cable crossings in the area.)
For long crossings, borings are typically taken at 700 ft intervals. For short crossings ( ft or less), as few as three borings may suffice. The borings should be near the drill-path to give accurate soil data, but sufficiently far from the borehole to avoid pressurized mud from following natural ground fissures and rupturing to the ground surface through the soil-test bore hole.
A rule-of -thumb is to take borings at least 30 ft to either side of bore path. Although these are good general rules, the number, depth and location of boreholes is best determined by the geotechnical engineer.
River crossings require additional information such as a study to identify river bed, river bed depth, stability (lateral as well as scour), and river width. Typically, pipes are installed to a depth of at least 20 ft below the expected future river bottom, considering scour. Soil borings for geotechnical investigation are generally conducted to 40 ft below river bottom.
The best conducted projects are handled by a team approach with the design engineer, bidding contractors and geotechnical engineer participating prior to the preparation of contract documents. The geotechnical investigation is usually the first step in the boring project. Once the geotechnical investigation is completed, a determination can be made whether HDD can be used.
At that time, design of both the PE pipe and the installation can begin. The preceding paragraphs represent general guidance and considerations for planning and designing an HDD PE pipeline project. These overall topics can be very detailed in nature.
Individual HDD contractors and consultant engineering firms should be contacted and utilized in the planning and design stage. Common sense along with a rational in-depth analysis of all pertinent considerations should prevail.
Care should be given in evaluating and selecting an HDD contractor based upon successful projects, qualifications, experience and diligence. A team effort, strategic partnership and risk-sharing may be indicated.
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