In the books "LeTourneau Earthmovers" and "Ultrahaulers", a proposed giant dump truck design by LeTourneau was mentioned. The proposed T-3320 (320 tons with a possibility of upgrade to 400 tons) was presented at MINExpo 92 with a flat side view display. The proposed truck was described as being a three axle truck similar in look to the 350 ton Titan 33-19. But instead of a forward axle for steering and two rear axles with dual wheels on each for load carrying, the T-3320 was supposed to have two FORWARD axles for steering with single mount tires and a SINGLE rear axle with dual wheels. I've read it attracted a great deal of attention so I always wanted to know what the proposed truck might've looked like.
I haven't seen them But, as we are talking about new designs, I've come upon these pictures of a Belaz 7570. Two double-mounted axels and articulated chassis. I think they're awesome, but if ever in production, don't know really how well would they fare.
I saw those a few years ago. Wasn't the display at MINExpo 04? IIRC, the BelAz 7570 was to be rated for 465 short tons. Which with a standard 10% overload would give it about 510 ton capability.