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 lineworkers in the air and setting transformers. In short, digger derricks are hardworking tools used to solve a variety of challenges.
However, given the versatility of a digger derrick, there are specific work practices that need to be followed, such as those for removing and setting poles. When work practices are not performed correctly, 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 a pole, you should know both practices are prohibited by manufacturers. They are prohibited because doing so can impose unknown loads and forces on the digger derrick that its key components are not designed to withstand.
Among the main components of a digger derrick that can sustain damage due to pole rocking are the pedestal, turntable, boom, cylinders, pole guides, subframe, outriggers and winch. All of these are costly to repair or replace if damaged, plus downtime for repairs can put the equipment out of service for extended periods.
Attempting to lift a pole that is frozen to, embedded in or fastened to the ground could shock load and cause an overload to the digger derrick components. So, instead of using the boom’s brute force, use a pole puller, which can provide much greater 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, assisting the pole puller. Once the pole is loose, the lift cylinders can then carefully lift the freely suspended pole while using pole guides to maintain control. The act of lifting should only be done based on the lift cylinder capacity, the load chart parameters and the number of parts of line. Do not use the pole guides to lift the pole; they should only be used to help control the pole as it is being lifted. Additionally, the rigging that attaches the pole to the load line must be below the balance point of the pole to keep the butt end heavy and down.
Once it has been lifted, it is critical to maintain control of the pole at all times. Shifting loads or losing control of the pole can cause failure of the pole guides, load line or rigging, resulting in unpredictable pole movement. Losing control can lead to serious injury or death as well as shock-loading, side-loading, and component damage or failure.
Know Your Load Weight
It also is critical to know the weight of the free-hanging pole before selecting a digger derrick for the task. If the load weight is unknown, charts are available to provide an approximate weight based on the material the pole is constructed from and the pole’s length. When determining weight, take into consideration anything that may be attached to the pole, such as crossmembers, transformers, insulators or wire. Consult the unit-specific load charts on the digger derrick to make sure it has the capacity needed to lift the load through the complete path that the load will travel, beginning with the extraction point and ending with the location of the final placement. You can avoid shock-loading the boom by maintaining control of the load at all times and only lifting loads that are not embedded in the ground.
Setting a pole, in most cases, provides fewer opportunities for equipment damage. The load line must be above the balance point of the pole and all components on the pole. Never use pole guides as support. 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 as well as damage to the pole guides themselves.
Alternate Equipment and Inspections
In some scenarios, alternate equipment might be necessary to dig a hole. The type of equipment used should be 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 – rather than a digger derrick – may be required to dig in areas of hard rock. Knowing which tools to use and having those tools available can save an operator countless hours, reduce wear and tear on equipment, and extend the life of the auger and teeth.
Finally, when inspecting a digger derrick, there are a few telltale signs that booms have been used improperly. Look for cracks, rust, loose paint, loose fasteners, deformation and other damage to the boom, pedestal and subframe. This may be evidence of shock-loading or overloading from using the boom to rock a pole or pulling a pole with a load line that was not freely suspended. Bent pole guides can be a sign that they are being used improperly to support the pole rather than guide it. Damage to the load line can be an indication of misuse from using the load line as a sling.
About the Author: Jason Julius works in technical support and training development for Terex Utilities (www.terex.com/utilities). He is a digger derrick practical examiner for the digger derrick operator certification through NCCCO. Julius also served on a task force to develop NCCCO foundation drill rig certification.
Setting Up a Pole Puller
A hydraulic pole puller is equipped with a heavy-duty steel base and slotted head for attaching a chain loop. To set it up, begin by placing the pole puller on the side of the pole vertically – either toward or away from the digger derrick boom – so the force exerted does not result in a side pull on the boom.
Next, drop the eye of the pulling chain over the slotted head of the pole-puller ram, loop the chain snugly around the pole and insert the chain end in the slot on the pole-puller ram. Make sure the chain is not kinked or twisted. Do not hook the chain and pole puller together using the chain as a choker chain around the pole. Both ends of the chain must be attached to the pole-puller ram to prevent overload of the chain and possible serious injury or death if the chain fails.
Attach auxiliary hoses from the digger derrick to the tool couplers on the pole puller. Use a section of nonconductive hose between the pole puller and the truck. Make sure there is no pressure in the lines before attempting to attach the hoses. The truck may need to be turned off to release pressure and allow the lines to be connected. Pull on each hose to make sure they are fully engaged with the tool couplers to prevent damage to the pole-puller fittings.
Wrap an appropriately rated sling around the pole above the pole’s center of gravity, attach the load-line hook to the sling and snug up the load line. Activate the pole puller by slowly operating the control valve to slowly lift the pole. Pole pullers can develop 40,000 to 60,000 pounds of force, so stand clear to avoid personal injury.
After each pull is made, winch up the load line to keep the line snug and reposition the boom as necessary to maintain control of the pole. Reposition the chain around the pole as needed to account for the pole’s tapering.
To prevent damage to the pole-puller cylinder rod when retracting, maintain the pole puller in an upright position.
Finally, use the pole guides and the load line to keep the pole vertical until it is freely suspended. Once the pole is suspended, use the load line and lift cylinders to remove it from the hole and place it in the desired location.