What we haven't asked is what part of the world the OP is working in. I think all the replies so far (including my own) have come from people in countries with well established heavy haulage industries, low public appetites for risk and effectively enforced highway rules. If it's not like that where you are, here's some ideas to start you worrying.
82 Tonnes is an abnormal load, but not beyond the bounds of the everyday abnormal, if you see what I mean. In theory, you ought to be able to move it on a 6 or 7 axle semitrailer even while living within the limits of the relatively restrictive UK (STGO 2000 Cat III) limits for abnormal indivisible loads.
Practice can be different - your aim is to ensure that
every axle is within its permitted loading and that you transmit enough (but not too much) weight onto the fifth wheel on the tractor, which depends on:
a. being able to calculate how far forward or aft the cg of your load can sit on the trailer before you blow any of those limits and
b. physically being able to fit the load that far aft or forward on the loadbed.
You need to understand what sort of gradients you will need your rig to negotiate: The steeper the hills it needs to climb, the more traction (function of weight on the driving axles) your tractor will need, and the further forward you will want to position your load. If you can't get the load far enough forward for that, then you'll need to start worrying about using a full trailer instead of a semi, pulled by a ballast tractor. As soon as you do that, your overall train weight skyrockets and bridge crossing becomes a major issue.
On the other hand, if you can't get the cg far enough aft to avoid overloading the tractor (this is a much less common problem), you might have to add a jeep dolly to the system.
You need to understand the height of your load's cg, how quickly it might be driven round bends (this might be quicker than you had intended if you're working in a part of the world where other people think it's helpful to shoot at passing heavy loads), what sort of side-slope you expect to have to negotiate, how fast the side-slope changes and, in particular, if there's anywhere those factors come together. This will guide your choice of trailer width. It's not impossible to roll a combination that seemed quite stable when you set out if your route involves an unexpected shift from one side of a dual carriageway to the other to get round some roadworks. That one also took some explaining, but I was much less closely involved.
You'll need to check that the physical dimensions of the loaded vehicle are acceptable for the journey. Worry most about length at the start end end of the journey and width, height and ground clearance on the highway in between.
The load needs to be attached to the trailer. Properly. Yes, even if you're only going to be going at a slow walking pace. Many people will tell you it stands to reason that something that heavy can't possibly slide off a trailer. These are people who haven't read the laws of physics and, at the subsequent board of Inquiry, will probably be nowhere to be seen. Not that I'm in any way bitter. There's a
good guide on the IRU's website.
Depending on where you are and whether you are going to venture out onto the Queen's highway, a move this size is likely to start to attract requirements for prior notification to the authorities, escort vehicles and specific permission from bridge authorities.
In my part of the world (and most people on this forum will be able to say the same) there's a well-established heavy haulage industry that does this sort of job every day, knows all the pitfalls, gets it right almost every time and has good insurance to cover the rare occasion when they mess up. As we've all said before, if you can possibly use one of these specialists, then you should. If that's utterly impossible, then at least go into the job with your eyes open.
A.