I have found dual-wheeled wheelbarrows with 2 wheels close to the center much more difficult to steer than a regular 1-wheeled wheelbarrow. Especially when the trail is uneven or rocky. I wouldn't recommend it.
For moving bridge sections, one of our trail crew members knows how to weld, and he fabricated a device that is basically a unicycle with a bracket and straps for holding 2 prefab bridge sections. The unicycle wheel, balanced in the middle, takes the brunt of the weight, with a crew member in the front and back to guide it. That works well, as long as the prefab bridge sections are about the same width & length.
When the terrain is too uneven to use that device, we use mover's carrying straps to take the weight off the arms and put it on the shoulder's of the carrier.
For moving small rocks or dirt over uneven terrain, I bought a canoe yoke, drilled one hole in either end, fed about 2-3' of rope though the holes, and tied the ropes to 2 buckets. Fill up the buckets with rocks or dirt, and carry using the yoke. You carry the weight on your shoulders, your arms don't get tired, and the buckets don't constantly bang against your legs as they would if you were carrying them by hand.
