Burying cable in concrete.

We've recently moved a large dynamic balancing machine in work and the company intends to get an outside spark in to reconnect it.
The labourer has been told to dig a trench 4" wide by 2" deep to lay the cable in and then fill over with a sand/cement mixture. The cable is 4 core armoured, (3 phase+neutral), approximately 6sqmm per core, may be 4sqmm but I think its 6.
To my mind 2" is nowhere deep enough unless its also covered by some sort of steel capping.
Are there any regs to cover this situation? The length of cuts, (there are 2 short sections as it runs in steel conduit behind a lathe for the better part), are about 3' and 5' if that helps. Its isolated via a 32A rotary switch isolater and a 32A mcb in the distribution board, no RCD in the circuit.

WHat will be moving over the cable when it is covered over?
Lorries, pedestrians, other?

Edit.

There are several regs. Look them up in the index of the good book.

It is cunningly disguised under the heading "Underground Cables"

522.8.10 Says
"..........Buried cables.....shall be at a suffiicient depth to avoid being damaged by any forseeable disturbance of the ground"

Obviously written around cables buried outside but the principle is the same.

Do risk assessment and install accordingly.

Remember those lovely Rawlbolts that get drilled into the floor to hold down benches etc etc ............

Thanks TTC, shall have to dig the bible out from the bottom of my wardrobe, (wife has had a blitz clean again!), as for the traffic it will only be partialy accessible to pedestrians, no trucks of any description can get into this area.

Ricicle, very good point, I've no doubt they will want to install some form of guards when it is completed so will have to make a note of that.

Thanks for the prompt replies lads.

Just had a read and think the best solution is a deeper channel and extend the conduit to run underground. Also think it would be a good idea to draw a sketch plan of the building noting where Dis boards/fuse boxes etc are located with their identifying tags and where there are buried cables/pipes etc.

Once again, thanks lads.