Rigging Spotlight
Handling Specialty Concrete Pipe
Top Left: A wireless load cell at each corner of the spreader told the pressure on a trident’ s concrete pipe.
Top Right: Each trident and the Cross T connector pieces were set in specific spots on the barge for the 1-mile ride out into Lake Michigan.
Bottom Right: Engineering analysis and 6-foot-by-12-foot-by-8-inch outrigger pads gave firm footing and made sure ground reactions didn’ t affect undergroudnd utilities or the seawall.
550-U. S.-ton capacity Liebherr LTM 1450-8.1 all-terrain crane that would be lifting the tridents and Cross T connector from land onto the barge.
To do that, Dearborn conducted a geophysical investigation and crane placement survey to locate and map any subsurface voids, underground utilities and structures such as seawall tiebacks and unconsolidated soils.
The survey also enabled Dearborn to assess whether the ground could support the crane reactions from lifting pieces that weighed more than 90,000 pounds with rigging.
Dearborn’ s investigation used visual inspection, an aerial drone to inspect the seawall and a handheld radio detector and ground-penetrating microwave radar to check the ground to a depth of 12 feet.
The study revealed the locations of the buried tiebacks that support the sheet-pile seawall as well as underground utilities.
Avoiding all of those dictated in part where the crane could sit.
Dearborn’ s analysis also recommended that the crane’ s four outriggers be at least 20 feet from the seawall, and that each one be supported by a 6-foot-by-12-footby-8-inch steel outrigger pad to reduce maximum ground-bearing pressure to about 4,500 PSF.
Using that ground-support arrangement, the big Liebherr crane made all six lifts from one location on 139 feet of boom and at radii to 85 feet.
Rectangular Spreader, Synthetic Roundslings
The trident placement project relies on two cranes, both supplied by Bay Crane Midwest.
All of the tridents and pieces of the
Cross T section that connects them were loaded onto a barge by the previously mentioned 550-U. S.-ton Liebherr LTM 1450-8.1 all-terrain crane.
In the near future, they will be lowered into their final positions on the lake bottom by a barge-mounted 100-U. S.-ton capacity Manitowoc 222 lattice-boom crawler crane.
Part of Dearborn’ s challenge in designing the load rigging was making sure the same rigging setups could be used by both cranes.
The other two rigging challenges were that the centers of gravity of the pieces had
been calculated but not verified, so the rigging needed to allow for slight variations without creating instability in the load.
In addition, because the tridents and the main Cross T section were all made of specialty prestressed concrete, the rigging would have to avoid overloading the pipe wall and connected joints.
To meet those exacting requirements, Dearborn designed the rigging system around a rectangular modular spreader frame( CMOD) that could be resized to accommodate each component’ s dimensions.
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October 2025 • www. cranehotline. com