A modular system of multipurpose rods for drilling soil is constituted by rods (1) crossed by an internal passage (2) for the passage of concrete, of substantially cylindrical shape, that completely crosses the rod; each of the rods is provided at the endings with a male insert (5) and a female insert (6) respectively, adapted to be plugged in one to the other for permitting the assembly in batteries of any length. The inserts (5, 6) are provided with transmitters (11, 11a) for transmitting the rotation along the whole battery of rods (1) and arranged for fixing elements that reduce the internal passage (2).