Tyre for a heavy vehicle of civil engineering type, comprising: - a crown part extended on each side by sidewalls, these sidewalls ending in beads, - a carcass reinforcement extending into the crown part, the sidewalls and the beads, this crown part comprising a tread having a wearing thickness and a crown reinforcement, the latter being situated radially between the tread and the carcass reinforcement, - the crown reinforcement comprising a protective reinforcement, a working reinforcement and an additional reinforcement, - the protective reinforcement comprising at least one protective layer (61, 62) comprising elastic metal reinforcers which form, with the circumferential direction, an angle at least equal to 10°, - the working reinforcement comprising at least two working layers (51, 52) having a respective axial width and comprising inelastic metal reinforcers crossed from one working layer to the next and forming, with the circumferential direction, an angle at most equal to 60°, - the additional reinforcement, centred axially on the equatorial midplane of the tyre, comprising at least one layer (71, 72) having an axial width at most equal to 0.9 times the shortest of the axial widths of the at least two working layers (51, 52) and comprising metal reinforcers which form, with the circumferential direction, an angle at most equal to 25°, - the tread being provided with a tread pattern design comprising at least one circumferentially oriented groove on each side of the equatorial midplane, the two circumferential grooves closest to the equatorial midplane delimiting a central region having a width equal to the mean distance between the said circumferential grooves, the central region being provided with a plurality of grooves of oblique or transverse orientation so as to form a plurality of blocks, this tyre being characterized in that: - the number of blocks in the central region over the entire periphery is at least equal to 42, - the mean axial distance between the two circumferential grooves closest to the equatorial midplane is greater than the maximum axial width of the additional reinforcement, this width being measured between the ends of the layers of this additional reinforcement that are axially furthest from the equatorial midplane, the axial ends of this additional reinforcement being offset axially towards the inside with respect to the said two circumferential grooves. - a crown part extended on each side by sidewalls, these sidewalls ending in beads, - a carcass reinforcement extending into the crown part, the sidewalls and the beads, this crown part comprising a tread having a wearing thickness and a crown reinforcement, the latter being situated radially between the tread and the carcass reinforcement, - the crown reinforcement comprising a protective reinforcement, a working reinforcement and an additional reinforcement, - the protective reinforcement comprising at least one protective layer (61, 62) comprising elastic metal reinforcers which form, with the circumferential direction, an angle at least equal to 10°, - the working reinforcement comprising at least two working layers (51, 52) having a respective axial width and comprising inelastic metal reinforcers crossed from one working layer to the next and forming, with the circumferential direction, an angle at most equal to 60°, - the additional reinforcement, centred axially on the equatorial midplane of the tyre, comprising at least one layer (71, 72) having an axial width at most equal to 0.9 times the shortest of the axial widths of the at least two working layers (51, 52) and comprising metal reinforcers which form, with the circumferential direction, an angle at most equal to 25°, - the tread being provided with a tread pattern design comprising at least one circumferentially oriented groove on each side of the equatorial midplane, the two circumferential grooves closest to the equatorial midplane delimiting a central region having a width equal to the mean distance between the said circumferential grooves, - the number of blocks in the central region over the entire periphery is at least equal to 42, - the mean axial distance between the two circumferential grooves closest to the equatorial midplane is greater than the maximum axial width of the additional reinforcement, this width being measured between the ends of the layers of this additional reinforcement that are axially furthest from the equatorial midplane, the axial ends of this additional reinforcement being offset axially towards the inside with respect to the said two circumferential grooves.