The year 2020 will be remembered for many things, including driving home the importance of a robust communications infrastructure. Investment is expected to continue to grow for the below ground utility infrastructure and with that the footprint of HDD.
This will further crowd the underground and right of ways which ultimately adds complexity to new installations since many of those utilities can cause interference.
Locating systems have seen significant advancements in their ability to deal with interference. Traditionally, locating systems had one or a few operating frequencies and the user was left to guess which was the best available option. Today, the most advanced systems scan the interference spectrum on the jobsite and pick the optimum operating frequencies from about 1,000 or so available and are therefore mostly able to sidestep the effects of interference.
But even those advanced systems don’t make steering decisions. Bore plans or various on-site calculations are the tools that the crew can use to help with some of the more complex navigation issues. These can be solved in different ways and this article will be discussing some of these methods.
Current Bore Planning Methods
Planning an HDD bore can be accomplished in many ways, ranging from a few relatively simple calculations, through using graph paper or a spreadsheet, to quite sophisticated bore planning applications. The very large, multiple thousands of feet crossings are typically highly engineered where significant geological and other relevant site data is used to, for example, estimate maximum allowable annular fluid pressures, max pull loads and bend radii in compound curves in addition to the intended bore path itself. Those are not the topic of this article.
Most commonly, a bore plan starts with a definition of the topology or the terrain, the length of the bore, the location, depth and clearance required for utilities and some key points, often referred to as targets or waypoints along the bore path. The waypoints are used to define things like minimum depth below a roadway or a specific point where a utility needs to be cleared.
Most plans using today’s methods are developed in the office, although there are also mobile applications such as Vermeer’s BorePlan and Subsite’s Field Scout. Vermeer’s web-based Vermeer Projects is a comprehensive solution that combines most aspects of an HDD project into a single solution.
Topography (or terrain) is critical to the accuracy of any bore plan. Information on terrain has historically been gathered via surveying where key points to survey are chosen along the bore path. How many depends on how much the terrain varies, but ultimately these are multiple feet apart meaning that the terrain in between is approximated using a straight line. The output is a rod-by-rod plan, where typically for each rod a desired depth and pitch are indicated. There will be potential inaccuracies with the planned depths, as these often will be based on the approximated terrain.
Often however, those plans don’t necessarily survive the first contact with the site, as entry or exit points have to be moved, the bore may have to be drilled in the opposite direction or a utility along the bore is discovered on-site which requires a modified bore path. There are therefore numerous reasons why planning in the field, in real-time, is often more advantageous.
Most HDD bores are not planned to a detailed rod-by-rod and in many cases that kind of planning may not be required. However, there are often sections of a bore where a rod-by-rod plan is very useful. For example, the crew needs to navigate a path over a utility about 60 ft out in front and there is an elevation difference that needs to be considered. Calculating how to steer those 60 ft can become complicated.
Digital Control has recently released the TeraTrak R1, a terrain mapping device built specifically to address these and other drill calculations. It functions by continually measuring the angle between its two wheels as well as measuring the distance traveled. By integrating the terrain grade measurements and distance traveled, a detailed chart of the terrain in 1-ft increments can be created. The data from the R1 is transmitted via Bluetooth to a mobile app where the terrain data is displayed in real time.
Let us consider the situation above and how the R1 would be used. At this point in the bore, no bore planning may have taken place, but the crew can create an ad hoc plan by mapping the terrain between the drill head and the utility. First, the current depth and pitch of the drill head (taken from the locator) are entered. Then, the desired depth and pitch at the utility is entered. The R1 is placed over the drill head and the R1 is then walked to the utility. Terrain data is collected, and the proposed bore path is displayed in real time as a red dashed line. The red dashed line indicates an invalid path, that is one that exceeds the user defined bending limits. This limit could either be for the drill rods or the product pipe being pulled back. Once the drill path turns a solid blue, a valid bore path has been created. This whole process can be completed in as little as 2 minutes.
Contractors planning bores with bore planning applications can very efficiently gather all the required data using the R1. Continuous terrain data, as well as the location and depth of all utilities and waypoints, can be exported to be used elsewhere. Bore planning aside, once the site data has been collected, various measurement modes allow the drill crew to answer any questions they might have relating to the terrain or utilities along the planned path.
Although there are many bores that do not require an engineered or detailed plan, the ever-increasing usage of HDD, will necessitate better data and more details about the terrain and utilities being crossed along the intended bore path. The TeraTrak R1 is designed specifically for that purpose, with the intent of helping to promote safer and more efficient installations.