A tread (1) for a heavy goods vehicle tyre is disclosed, the tread (1) having a total thickness corresponding to the thickness of the material undergoing wear during rolling, this tread (1) having, ina new state, a rolling surface (10) for contacting a road surface when rolling, and comprising at least one hidden cavity (2) for forming a new groove opening onto the tread surface (10) after a predetermined partial wear, the hidden cavity (2) comprising two opposite side walls (21, 22) interconnected via a radially inner bottom (23) and via a radially outer top portion (24), the top portion (24) of the hidden cavity (2) being provided with a plurality of fine grooves (25), the depth of which extends radially outwards from the top portion (24) delimiting the hidden cavity (2), which fine grooves (25) extend in a direction that forms an angle of at least 40 degrees relative to the main direction of the hidden cavity (2).