9 July, 2018
Photo: Omega Morgan uses wood round mats for smaller cranes and consider ground bearing capacity.
The most important part of crane setup and operation is assuring proper ground stabilization. American Cranes & Transport spoke with industry experts about how they approach ground stabilization when it comes to crane mats, pads and cribbing for the various projects they perform.
At Imperial Crane Services, a lift planners’ method for ground stabilization is the same, regardless of the crane size or type being used.
“Although the client assumes responsibility for the ground and soil conditions in the area where the crane is to be stored, parked or operated, Imperial estimators and planners assist the client with the requirements of the crane being used to be properly supported, and to identify and mitigate any potential hazards related to the ground conditions on the site,” said Larry Eckardt, vice president of operations, Imperial Crane Services. “We provide the ground-bearing pressure created by the crane in use and offer the necessary matting to achieve acceptable conditions to perform the work safely.”
Planning is key
According to Kate Lampson, director of strategic communications at Lampson International, regardless of what type of crane is used to make a lift, there are several categories that need to be considered when factoring in ground stabilization.
“These include potential hazards to people, complexity of the load handling activity, adverse impact from environmental conditions, lift equipment and rigging capacity and/or performance, adverse commercial impact, site requirements unique to the load handling activity and federal, state and local safety requirements,” Lampson said. “One of the main issues associated with planning any type of a lift is ground preparation and stabilization. There are several major categories that will help determine if the lift is either standard or critical in nature, and each category has multiple related items ranging from determining accurate load information, such as verifiable weight to the location of the center of gravity, verifying the allowable ground conditions, establishing a communication plan and controlling site access.”
Some of the more complicated ground stabilization issues that Imperial’s crews have faced include working on suspended structures like bridge decks with specific limitations to ground bearing pressure.
Lampson International has always used their own steel mats under Lampson Transi-Lift crawler cranes. Lampson now offers short and long-term crane mat rentals.
Eckardt said in these cases, engineering related to the shoring process of the structure to meet the level of stability required to support the pressures applied by the crane can get very complicated. Proper evaluation and planning are always key.
“All our cranes are provided with mats that are sufficiently sized for the ground-bearing pressures generated by the crane,” Eckardt said. “When it comes to selection of cribbing products, it is always about the application. We utilize several types of matting depending on the conditions and crane type; hardwood, synthetics, steel plating and fabricated steel matting. All have their strengths and weaknesses in various conditions, whether it is the weight/size of the cribbing related to transport and set up, or the effectiveness of the cribbing in various conditions, uneven ground, or water/moisture content of the soil, as well as the specific ground bearing pressure values set by the client.”
Lampson International uses steel mats under Lampson Transi-Lift crawler cranes, and the company now offers short and long-term steel crane mat rentals.
“We manufacture our crane mats at our facility in Washington state and offer Mudboats as well as conventional steel crane mats,” said Lampson. “Our Mudboats measure 9 feet by 50 feet and 9 feet by 25 feet and are moment connected for continuous bearing. Our steel crane mats measure 16 feet by 14 feet and include fork pockets for easy placement. Our mats are good for various applications such as load spreading, ramps, temporary bridging and crane runways to name a few.”
Omega Morgan uses various types of wooden round crane mats for smaller cranes, and they look at customer-provided ground-bearing capacity information to ensure that the mats are adequate to spread the load and stay under the required PSF, according to Kai Farrar, project engineer, Omega Morgan.
Omega Morgan uses the Duerr method to calculate track pressure and ground pressure and to determine a wood crane mat configuration to stay within the proper ground-bearing capacity. The same applies to Omega Morgan’s steel crane mats that are most often used with all-terrain cranes.
“We have designed and fabricated steel mats for each of our AT cranes that generally keep ground bearing pressure under 3,500 PSF,” Farrar said. “We also have various sizes and thicknesses of steel plate as well as fabricated I-beam bunks, if we need to have even lower ground pressure.”
Below the surface
“As a crane company, we don’t determine the ground-bearing capacity of the site,” said Farrar. “The site owner or general contractor is responsible for determining the site ground capacity. Soil studies to determine ground capacity are generally conducted when there is no historical data for a site, when the force imposed by a crane is unusually large or there are buried structures and/or utilities.”
Lampson added that whether is a rough terrain crane, a boom truck or a heavy crawler crane, the company takes ground preparation very seriously.
Another expert in ground preparation, Dearborn Companies is a 65-year-old consulting, engineering firm and testing company that prides itself on tackling the most challenging crane and rigging jobs.
“What makes us somewhat unique is that we actually have the organic Ground Penetrating Radar (GPR) capabilities,” said Mike Walsh, president, Dearborn Companies. “This includes 3-D laser scanning along with engineering services. So, we can do data collection and document ‘as-is’ conditions and engineer that all out. That also involves clearance studies for tail swing, boom swing, load swing, getting the crane in, getting the crane back out, etc.”
A big part of the ground preparation process also comes down to the workflow, Walsh said, making sure you’re collecting data that’s being georeferenced. Then it comes down to the interpretation of that data.
“There are days where that can be as much art as it is science,” Walsh said.
At Imperial Crane Services, the method for ground stabilization is always the same.
Rules and regulations
Effective ground stabilization wouldn’t be successful and safe without a set of guidelines for the industry to heed.
“The OSHA regulations place the responsibility of the ground and the ability to support the crane on the controlling entity of the jobsite,” said Billy Smith, executive vice president, NBIS. “The ASME/ANSI B30.5 safety standards require the site supervisor and the lift director to make sure the ground conditions are capable of supporting the crane and its intended load. The crane company should provide the ground bearing pressure below the crane outrigger pad and the support materials they are using to the controlling entity, site supervisor and/or lift director.”
Smith emphasized that ground stability is not the sole responsibly of the crane company. It’s important with the usage of large cranes that ground conditions are considered in detail.
“The problem, and also the challenge, is in the small crane industry where a crane may do three to five jobs a day and they are in and out in a couple hours,” Smith said. “Additionally, a rough terrain crane may move on a jobsite multiple times in a workday and set up in several locations. Therein lies the problem and the ground PSF beneath the outrigger may be an unknown and the lift still be successful. More than often this is the case.”
Certification exams from the National Commission for the Certification of Crane Operators pays significant attention to ground stabilization standards and best practices. The majority of NCCCO operator examinations address ground stabilization. While the language does vary, according to Graham Brent, Chief Executive Officer, NCCCO, elements of concern include but are not limited to: weakness below the surface, such as voids, tanks, and loose fill; weakness on the surface, such as retaining walls, slopes, excavations, and depressions and firm, drained, and graded ground conditions for adequate support. Operators must also know the proper use of mats, blocking, or cribbing and outriggers or crawlers, as they affect the ability of supporting surfaces to handle the expected loads of the operation.