Distance Between Earthing Rods

2.2 times the driven depth between each rod (IEEE, BS7430).

So, 2.4m deep set needs to have ~5m separation. Remember, they don't need to be in a line, they can be deployed in a grid if space permits.

A grid ('duplex') is considered better configuration because if one of the conductor runs is cut, you still have an operational earth because the fault current can flow down the remaining leg, whereas, a single line ('spur') has to be sized to take the entire current and is lost when damaged.

Make sure you conductor is sized to cope with an imported fault from the HV suppply as well; your DNO should be able to provide you with calculated fault data.

Have fun.

as for my knowledge is concerned your earth rod should be 3 meter deep and the distance between the rod is 15 m as per standard