While the Bagger 293 is an awesome piece of machinery, it is mostly static, and meant to displace large quantities of dirt. For destroying a wall it would be extremely inpractical.

The mad inventor labs would like to introduce you to the "MOLE":

Tunnel boring machines have several advantages over the Bucket wheel excavator:

• It is a much squatter machine, specially if you don't need to create a long tunnel: most of the structure you see behind the shield is for creating the supports, so a wall boring machine would be much shorter.


• Is easier to armor: The front face shield is already heavily armored, for the rest you can cover it with plates

Think of the TBM as a higly advanced ram.

Of course, it is still quite heavy and a warfare oriented version will probably have tracks instead of wheels.

EDIT: Sebastian Lenartowicz points that in fact, someone had already this idea. In Avatar, the last airbender, the fire nation uses what would be a heavily armored tunnel borer to perforate a giant wall. It also solves one of the problems an aboveground TBM: the machine uses a kind of wormlike displacement where some kind of metal hooks perforate the earth to keep the bore moving forward instead of following the path of least resistance and stop moving when it arrives to the wall.

(and yes, I watched the episode to write this :D)

Can it breach a wall? Especially with extra armour and features? Probably with no problem.

The problem in this case are twofold:

1. This thing moves veeeeeeeeery slowly. And the main problem with any siege machine is that it can be destroyed (or stopped) before it arrive at point. Making a wolf pit in it's path with explosives would probably stall the machine for days if not weeks


2. 
   

   Why would you need to break the wall if this machine would make it much easier to go over it. Look at this! This is moving tower giving you (attackers) two advantages. Higher ground, so you can shot, throw, spit, plummet, cast, hurl or fling anything at the defenders. Second thing is that you just need to extend the plank to find your troops behind enemy walls. And it's hard to stop the landing when you have people shooting at you.

   
   
   

   This machine would be much batter as a siege tower than bettering-ram. Because a) destroying walls take precious time b) when you siege that "castle" you have a wall to fix. With just hopping over the wall you gain time and save some in the future.

   
   

The major problem I see is not if the thing can tear down a wall (I think it can with little effort), rather how to take it there and how to take it away.

Super-heavy tanks have often been proposed in the past, and always slammed against the problem of their size, see for example the Panzer VIII Maus:

Development of the Panzer VIII Maus had highlighted significant problems associated with very large vehicles, such as their destruction of roads/rails, their inability to use bridges and the difficulty of strategic transportation by road or rail. The bigger the vehicle, the bigger these problems became.

In a mine you have a dedicated surface to move the machine, while around a city you might lack the infrastructure to allow the machine to move. Moreover, its large footprint is subtracting space to other troops, so while it moves in you have to move away someone else, and once it has opened a breech in the walls you have to move it away quickly (the thing is all but fast) to ensure your troops can access the breech.

Else it might be taken by the defenders and act as an outpost for them.

When you say 'like' the Bagger 293, are you talking about a re-purposed mining machine or something that looks similarly cool but was designed from the tracks up as a siege tool?

As Mazura has mentioned (more than once ;-) ) a standard bucket-excavator isn't really the right tool for attacking reinforced walls. Replace the bucket wheel with a smaller diameter, toothed cutting wheel and you would have something that can chew through walls - when it eventually reaches them. It's still going to be slow.

If, on the other hand, this monster is purpose-built for siege work, there are all sorts of things you can do to make it more effective:

• Replace the cutting wheel altogether and fit a multi-disc boring-head, similar to the Mole described in another answer.




• Design your motive unit so it can advance on the walls at a reasonable speed (things like the Bagger don't need to move more than 0.5km/h; the mine isn't going anywhere)




• Fit steel plate armour around the boom to provide safe passage for your invaders and have turret mounts to provide covering fire.




• Design the Fort Breaker such that it can be transported to the siege
  in easily moved pieces and assembled near to the target. For example,
  each of the Bagger's track units could become a self-propelled
  carrier unit, small enough to fit onto a tank-transporter size
  vehicle. The mining-head could fit into the a same size vehicle.

You could even go the Transformers route and have each Track unit act as a battle-tank in it's own right until the siege engine was needed. Then you line them up; fit the battle-harness, boom and mining-head; then charge!

Your Iron Guard wouldn't stand a chance against that!

Use the right tool for the right job.

If the cab is close enough to be in range of flaming oils, you'll have to run snorkels out the back until they are out of range, for both the air intake and the exhaust.

This is a demolition shear that goes on the end of the arm. It's designed to cut scrap steel, but it will cut anything you put between its jaws. If those were fireproof steel braided hydraulic lines there'd be nothing anyone could do to stop it eating walls.

This is an excavator with a hydraulic chisel attached to it. Steel reinforced concrete walls have rebar inside them, so you'll need to crack it into pieces that are still stuck to each other, and then finish up with the shear.

If it's still in range of the enemy, erect a tower crane that can pick it up and move it between two work sites. If they also have an 'excavator', by the time they move their crawler over to ours, we'll be picking it up, swapping heads, and carrying on. That is, unless they also have a tower crane (if they do, none of these above ground solutions work).

Why worry about breaking the wall at all? (after conquering the fortress, you want to use it for yourself, right?)

The thing is high enough that it can easily serve as a bridge over the wall. Instead of punching a hole through, make a pathway on top and walk in, then slaughter the defenders inside, and enjoy an undamaged fortress.

Opposed to everyone here:

NO IT ABSOLUTELY COULD NOT breach an "a large steel reinforced wall" [as by OP]

That thing is made vor moving DIRT.
As in normal, regular soil.
Brown coal (which this excavates) is NOT in rock, it's at mos buried in gravel or dirt.

It can barely break frozen soil, how would it be able to destroy concrete, let alone steel-reinforced one?

Sorry op, but at least the front part would have to be replaced by actual mining equipment in order for this to work.

Alternatively: Use the big arm as a siege tower, from which your army runs onto the wall.

Trojan Horse

It's already inside the wall - doing, or sitting where it used to do, its thing. It's a 100 million dollar piece of equipment. That's why there's a wall.

There could be some good plot stuff about how your guy knows this ancient tech and thinks he can at least get the tracks working again. Saying that even if the treads broke right out of the gate, it'd still go about forty feet and then we just wiggle the arm until it breaks if we can't get it to move down.

Capture it and then creep over to the wall until it kinda smashes through and/or falls over and makes a ramp. Yea! Charge!