Depends on the motor, drivetrain, and how it's being operated. Typically, you can expect between five and seven miles per gallon in normal driving while loaded.
A dump truck with two drive axles.
In idle? The configuration of the tractor has nothing to do with determining that. It's the motor which does, and the consumption rate in idle for a motor would be the same for a tandem axle dump truck as it would be for the same motor in a road tractor, box truck, quad axle dump truck, cement mixer, etc.
Typically, around 15 tons.
A tandem dump truck is as normal as any other dump truck. Tandem simply indicates that it has two drive axles (as opposed to a single axle, which only has one). A tandem dump is typically allowed to gross at 54,000 lbs. From there, some dump trucks have additional axles (lift axles) which allow them to haul more weight. They're named in accordance with the number of axles behind the cab (i.e., not including the steer axle). So a tandem dump with a single lift axle would be referred to as a tri-axle, with two lift axles it would be referred to as a quad axle dump, with three lift axles it would be referred to as a quint axle dump.... at four lift axles, they're typically referred to as 'centipedes'.
40,680 lbs.
Depends on the truck and configuration (e.g, tandem axle dump, tractor-trailer end dump, etc.).
17 tons
A tandem axle (ten wheel) dump truck can typically weigh between 20,000 and 25,000 lbs., depending on make, model, steel or aluminum dump body, etc.
You would have to define "typical". A dump truck could be anything from a Class 1 to a Class 8 truck. Assuming you consider a tandem axle dump truck to be the norm, the permitted GVW in most states would be in the vicinity of 54,000 lbs.
Which weight? Gross weight? Tare weight? What configuration? 1 ton pickup? Single axle Class 7/8 truck? Tandem axle truck? Tri-axle truck? Quad axle truck? Quint axle truck? Centipede? "Superdump" quint with Strong Arm? Transfer truck? Tractor-trailer end dump, or belly dump, or side dump? Try to narrow down the variables a bit. There's really no way of knowing what an "average" dump truck is without knowing statistics of how many single axle, tandem, tri-axle, quad, quint, centipede, and superdump dump trucks are out there - to the best of my knowledge, no such statistics have been compiled. At the company I work for, our tandem axle dumps (with steel dump bodies) weigh between 23,000 and 24,500... the 23,000 lbs. trucks are the Peterbilt 330s, and the 24,500 lb. trucks are the Kenworth T800s with "rock tub" steel bodies, high lift gates, and split gate beds. These are the tare (empty) weights, not the loaded weights.
Three - the two drive axles, and the steer axle.
A dump truck with two (tandem) rear pulling axles supported by a third fixed axle located in the middle of the truck which only reaches the ground after a certain amount of load weight.