Typically, around 15 tons.
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.
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'.
Depends on the truck and configuration (e.g, tandem axle dump, tractor-trailer end dump, etc.).
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.
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.
That's going to depend on the dump truck's configuration. It could be a single axle, tandem, tri-axle, quad axle, quint axle, centipede, frameless end dump, framed end dump, etc.
Tandem axle dump truck. In some states, you may be able to put up to 15 tons on a single axle with an additional lifting tag axle.