In April 1992, a crew driving a new set of pilings adjacent to Chicago’s Kinzie Street bridge inadvertently placed one of the pilings slightly off the desired location. The piling punctured a long-disused railroad tunnel below the river’s floor. Within hours, the city’s downtown area had shut down, as a torrent of river water flowed through the underground tunnel network and swamped basements of buildings like City Hall, the Merchandise Mart, and the Chicago Hilton and Towers Hotel. The cleanup took weeks and cost millions.
The so-called Chicago Flood of 1992 represents an extraordinary example of what can go wrong when construction crews drive pilings. The Kinzie Street pilings were intended to keep barges and boats from striking the bridge structure, but pilings are also widely used for providing support for the construction of foundations for buildings, bridges, and a variety of other structures.
Pile drivers use heavy weights and a tremendous amount of force to pound poles deeply into the ground. The sheer power of a pile driver and the potential for damaging below-ground features underscores the important role of safety in piledriving operations. Besides the potential for injuries to workers, an incorrectly placed pole can compromise the structural integrity of nearby foundations or ground features. It also has the potential to puncture underground utilities such as sewers and gas lines, sever electrical conduits and communications cables, and in the case of Chicago, trigger an expensive disaster.
That’s why pre-construction planning is crucial in pile driving operations. Planning for safety should incorporate an equal focus on workers, the equipment they’ll use, supports that are provided, and the specific tasks that are being performed.
Safety planning for pile driving operations begins with a thorough study of the worksite. Access must be provided for personnel, the equipment that will be used on the site, and the materials that will be employed during the process. In addition, space must be available for storage of tools and equipment, protecting hazardous materials such as welding gases and fuels, and for washing out concrete trucks and other equipment. Much of the material used in pile driving is large, so safe spaces must be provided for delivery, assembly, pickup, laydown, and disassembly.
Particular consideration should be given to the stability of the ground on the site, including strategies for dealing with stormwater. If the site is muddy, drainage or dewatering equipment may be used to enhance stability, and walkways may be provided for workers (with any that are more than four feet high incorporating handrails and toe boards).
The safety plan should also consider how spoils will be handled and where they will be placed. Temporary spoils should always be kept more than two feet from the edge of excavations or driving locations, to ensure that they will not fall into the excavated areas. Permanent spoils should be moved some distance away from the work. The area for the storage of materials should be planned to provide safe storage and access without the potential for sliding or collapsing.
Trenching and excavations are often a part of pile-driving activity. Obviously, the site should be studied for underground utilities, which should be clearly marked. Nearby structures that may be affected by excavating should also be considered, with sheeting or other measures taken to prevent possible damage. Any trenches that are more than three feet deep require exit ladders within 25 feet of worksites, with toenailed braces to keep the ladders from slipping.
If shoring will be installed, that should be done from the top down. Any hydraulic shoring must be inspected at least once each shift to verify that there is no damage or equipment failure that would present a hazard to worker or the site.
When pile driving equipment arrives at the site, inspect it for any damage and deterioration that could impact its function or create a safety hazard. All equipment, including ropes, cables, slings, and fittings must be inspected. Rigging operators need to ensure that the hoist or crane is assembled properly, that all controls are working, and that any needed adjustments are made. Any damage or kinks to wires, ropes, chains, or cables call for an immediate replacement.
All workers on a pile driving jobsite should wear the correct Personal Protective Equipment, and that equipment should be inspected before each shift or when resuming work after a break. Workers who will perform welding, cutting, grinding, or similar tasks should also wear suitable eye and face protection. Anyone working directly with cement or other potentially irritating materials should wear the correct gloves, such as canvas gloves coated with neoprene.
Although pile driving can be a complicated process, general safety rules that should be familiar to every worker will provide the greatest protection. Workers should have safety training for any task they perform. Piles should be lifted only with the appropriate slings or similar equipment, and workers should maintain a safe distance while piles are being hoisted. (Works should never stand below a hammer or core.)
As pile locations are being pre-excavated or jetted, operators must be careful not to undermine the rig or any nearby structures. When augers are withdrawn, rocks and chunks of earth should be removed before they are inserted. If the piles are not going to be placed in the holes immediately, they should be covered to ensure that workers and equipment cannot fall into them.
While driving is underway, the operator should maintain light pressure on the hammer drum brake to keep the hammer under close control, and stop immediately if the pile breaks or otherwise malfunctions. He should also pay close attention to the hammer hose to ensure that it doesn’t get caught in any moving parts. If pipes are cut to be flush with the ground, cover the heads to protect them from collecting foreign matter and to ensure that nobody steps into the pile.
Finally, regular inspections of the work area and equipment are vital to ensuring everyone’s safety. At the very least, the site and all equipment, including the controls, should be checked by supervisors at the site, and any deficiencies must be addressed before work resumes.