What type of CDL do you need to drive a dump truck?

For a typical tandem axle dump you need a class B CDL.

Of course, dump trucks vary greatly in terms of size, as well. In Colorado, tandem axle dump trucks are the norm, but they also pull pup trailers, and those combinations require a Class A CDL. Your dump truck might be something like a Ford F650 - rated at 26,000 lbs., and it doesn't require a CDL. However, if you attach an eight ton equipment trailer to it, now you have a combination requiring a Class A CDL. So, basically, you go by the CDL classes:

Single vehicles or combination with a GCWR of 26,000 lbs. or less: No CDL required

Single vehicles with a GVWR of more than 26,000 lbs: Class B CDL required

Combination vehicles with a GVWR of more than 26,000 lbs., in which the vehicle in tow (i.e., trailer) has a GVWR of more than 10,000 lbs: Class A CDL required