Manufacturers of construction machines and those who use them are rightly concerned that equipment is operated correctly to complete work in a timely manner without accident or injury. Safety is a key element in written guidelines and training for proper equipment operation. While there are general safety procedures that apply to most construction activities, the many different types of equipment require specific procedures that address individual machines and job characteristics.
Basic Good Practice Guidelines
The Common Ground Alliance (CGA) Best Practices, introduced in 2003 and updated annually since 2006, is considered the industry standard for preventing accidental damage to underground utilities. The guidelines include general excavation, trenching and horizontal directional drilling (HDD). These categories employ different types of equipment, each requiring operational and safety training.
The North American Society for Trenchless Technology (NASTT) publishes the “HDD Good Practices Guidelines,” which specifically applies to the operation of horizontal directional drilling equipment, including recommended safety procedures.
The HDD industry developed rapidly after the first drill models designed for utility work appeared on worksites in the early 1990s. Early equipment manuals and training did not ignore safety but primarily explained how to operate equipment that was new to users. Early directional drilling installations were “tests” of a new, unproven technology.
Today, HDD is an accepted method of construction specified in many project plans for designated segments of a project. In some instances the bore may be the entire project, a long river crossing, for example. Many projects contain multiple bores at locations along a utility’s route, with specifications for each bore written into the plan developed by design engineers.
On such large projects, a HDD subcontractor should evaluate the HDD segments and be able to suggest potential problem areas or ways to make these installations more efficient.
Typically, the operation of drill rigs today is by experienced personnel familiar with their equipment and the HDD process. Basic functions of drill rigs may be similar, but manuals and training for operating individual models — which clearly outline proper use and give safety warnings — should be used.
Plan the Work
The focus of these suggested HDD good practices is planning and other critical elements in making HDD installations. Few guidelines are directly related to “running” the machine.
Whether performed by the project owner, consulting engineer, prime contractor or the contractor for HDD segments, every HDD installation should begin with a plan. An important element of a comprehensive design plan is identifying existing utilities along a bore route. Working around buried facilities unexpectedly during drilling or excavation can create safety hazards, waste money paying crews to stand idle while planning adjustments are made and usually result in scheduling delays.
Diameters of backreamers to be used and the product to be installed must be considered during planning. Many jobs have been complicated when a reamer hits a pipe during pullback that was missed by the smaller drill head making the pilot hole.
Before moving onto a job the HDD crew members, and especially the drill and tracker operators, should carefully review the bore plan. The more a crew knows about the job, the less risk of surprises. Blueprints, right-of-way, geological information and maps of existing underground utilities should be reviewed. Existing or planned structures, elevations and proposed work scheduled at the same time should all be investigated. For complex installations, bore planning software assists with guiding the drill head to the exit point and can produce an accurate as-built map when it is complete.
Calling 811 to reach the local One-Call agency is the first step in having existing utilities located and marked. However, the drilling crew’s responsibility for avoiding accidental damage to buried utilities does not end with a One-Call notification. The CGA reports that in 2012, 74 percent of utility damage events occurred on jobs where locate tickets had been written. In these cases, the excavator knew where utilities were marked but proper precautions were not taken to confirm that the locates were accurate or improper drilling procedures were followed. One-Call’s responsibility doesn’t extend to improper drilling practices or carelessness.
However, One-Call only arranges locates through One-Call members, and not all utility providers are members. Therefore, it is possible to encounter active utilities on construction sites that have not been located.
One-Call locates are also limited to utility easements and may not be made on private property. This includes infrastructure owned by business parks, universities and other educational complexes, as well as military and government installations. Responsibility for making these locates falls on the facility owner, primary contractor and often the subcontractor actually doing the drilling.
Even when utilities appear to be properly marked, a survey of the site should be conducted to look for signs of unmarked utilities such as sunken areas indicating a previous trench, utility facilities without overhead lines, light poles, manholes covers, outbuildings with utilities, meters etc. It is recommended that drillers also have locating equipment to verify locates. Additionally, utility maps should be referenced to determine which utilities are in the area and whether locations agree with markings.
The best way to be absolutely sure where a buried utility is located is to uncover it. With the growing emphasis on preventing accidental utility hits, many project owners and regulators are requiring visible confirmation in specific circumstances.
Work the Plan
Before moving to the worksite, drillers must verify the drill unit is right for the job. The unit should be big enough to complete the pilot hole and pullback, but not too big for available space. Downhole tools and fluid additives must fit soil conditions, and all needed safety, support equipment and accessories must be gathered.
The drill unit must be set up in a location that will allow anchors to be driven outside of tolerance zones. The drill unit must be positioned at the necessary set-back distance for the entry pitch needed for the pipe bend radius to reach the specified depth. The machine’s electrical strike system must be connected and confirmed to be operational.
To stay on target, the path of the pilot bore must always be monitored by surface tracking or wireline. The tracker operator and driller comprise the core of the drilling crew and must remain in constant contact while making the pilot bore and product pullback.
Short, relatively straight shots in good soil are usually easy to complete. Longer, more complex pilot bores with multiple elevation and left/right direction can be simplified by the use of planning software that monitors bore progress in real time. This software also documents the installation with an as-built map, which is a requirement today of many prime contractors and project owners.
Long bores may have an exit point that the drill operator cannot see. Therefore, it is crucial that communication with the tracker ensures no one is in the exit pit when the drill string is moving. Using an exit pit control system, which allows the exit pit workers to disable the drill string controls, is recommended.
Potholing to confirm locations of existing utilities can be performed during planning, but most often they are made on site before a bore reaches pothole locations. The preferred potholing method today is by vacuum excavators using “soft” excavation technology employing either high-pressure water or air to displace soil around pipe or cable. On most HDD sites, compact trailer-mounted vacuums are used for potholing and keeping work areas clear of drilling fluids.
With careful planning and proper operation of the drill unit which follows established “good practices,” experienced directional drillers have made horizontal directional drilling an essential method for installing underground utilities. In fact, it is often the most practical and sometimes only way a project can be completed.
Susan Harmon, P.E., CSP, is the Product Safety and Compliance Manager for The Charles Machine Works Inc.