By Jason Julius, Technical Support and Training Development for Terex Utilities
Digger derricks are among the most versatile tools on a utility line construction project. They are built to tackle a myriad of tasks – from digging holes and lifting and setting poles to turning in screw anchors, putting linemen in the air and setting transformers. Like the people who use them, digger derricks are hard working tools used to solve a variety of challenges.
However, with this tool’s versatility, there are work practices that need to be properly managed, such as removing and setting poles. If not done properly, equipment can be damaged. If you’ve ever used a digger derrick boom to rock a pole loose or used the load line to forcibly remove the pole, you should know this practice is prohibited by manufacturers. It is prohibited specifically because it can impose unknown loads and forces that key components were not designed to withstand.
Among the main components of a digger derrick that can experience damage due to pole rocking are the pedestal, turntable, boom, cylinders, pole guides, subframe, outriggers and winch – none of which are inexpensive to repair or replace if damaged. Downtime for repairs can put equipment out of service for extended periods.
Using a Pole Puller
Instead of using the boom’s brute force, a pole puller must be used to loosen the pole. A hydraulic pole puller is equipped with a heavy-duty steel base and slotted head for attaching a chain loop. Attempting to lift a pole that is frozen to the ground or embedded/fastened to the ground could cause shock load. The unknown load could cause an overload to the digger derrick components. Instead, use a pole puller, which can provide much higher force to loosen the pole.
In extreme cases, it may be necessary to dig one or more holes with the digger derrick auger alongside the pole to loosen the soil to assist the pole puller. Once the pole is loose, then the lift cylinders can be used to lift the pole while using the pole guides to maintain control of the pole only, not lift. The actual lifting should only be done within the lift cylinder capacity, the load chart and the number of parts of line – do not use the pole guides to lift the pole. The pole guide should only be used to help control the pole once it is vertical and to help plumb the pole. The rigging attaching the pole to the load line must be above the balance point of the pole to keep the butt end heavy and down.
Once the pole is lifted, it is critical to maintain control of the pole at all times. Shifting loads, violent movement of the boom or pole, or losing control of the pole can cause pole guide failure or load line or rigging failure. Losing control of the pole may lead to serious injury or death along with shock loading, side loading, and component damage or failure. Use slow movements and feather the controls.
Likewise, it is critical to know the weight of the pole before selecting a digger derrick and positioning it for the task. If the load weight is unknown, charts are available to provide approximate weight based on the material the pole is constructed from and the length of the pole. When determining the weight, also take into consideration if the pole is wet or wrapped plus anything that may be attached to the pole such as cross members, transformers, insulators, and wire. Consult the unit specific load charts on the digger derrick to make sure the digger derrick has the capacity needed to lift the load through the complete path that the load will travel – beginning with extraction point and ending with the location of the final placement. You can avoid overload and shock loading of the boom by only lifting loads that are not embedded in the ground and maintaining control of the load at all times.
Setting a pole, in most cases, creates fewer chances for causing damage to equipment unless overloaded. The load line must be above the balance point of the pole including all components on the pole. You should never use the pole guides to support the pole. They are meant to guide the pole, helping to keep it under control, and reduce the chances of causing side loading or shock loading to the boom and damage to the pole guides themselves. When setting or removing poles near energized lines use line cover up and pole covers to protect against energizing the pole. All ground personnel must use insulating tools, insulating gloves, or insulating boots if contacting the pole.
In some cases, alternate equipment might be necessary for digging the hole in the first place. The type of equipment used is dictated by the ground conditions that need to be augered. For example, in hard rock areas a core barrel can be used instead of a standard auger to increase productivity. Areas of shale require different types of tooling than sandy or clay soil conditions. In addition to switching tooling, a pressure digger may be required to dig in areas of hard rock instead of a digger derrick. Knowing which tools to use and having those tools available can save the operator countless hours, reduce wear and tear on the equipment, and extend the life of the auger and teeth.
Finally, when inspecting a digger derrick, there are a few tell-tale signs that booms are being used improperly. Look for cracks, rust, loose paint, loose fasteners, deformation or other damage to the boom, pedestal, or subframe. This may be evidence of side loads, shock loading or overloading from using the boom to rock the pole or pulling a pole with the load line that is not freely suspended. In addition, bent pole guides can be a sign that they are being used improperly to support the pole or push against the pole, rather than guiding it. Damage to the load line can also be an indication of misuse by cuts and wear from using the load line as a sling or side loading. If the load line is not vertical there is a side load on the boom.
This material appears in the November 2021 issues of the ACP Magazines:
California Builder & Engineer, Construction, Construction Digest, Construction News, Constructioneer, Dixie Contractor, Michigan Contractor & Builder, Midwest Contractor, New England Construction, Pacific Builder & Engineer, Rocky Mountain Construction, Texas Contractor, Western Builder