A rock crushing unit for widening a pilot hole realised on rocky terrain, wherein: it comprises a main body dimensioned so as to insert in a pilot hole realised on rocky terrain and activatable in rotation with respect to the axis thereof; it comprises a first plurality of crushing elements for crushing rock; the rock crushing unit is configured so that when in use, the action exerted by the crushing elements of the first plurality of crushing elements on the lateral wall of the pilot hole determines the crushing of the lateral wall of the pilot hole and thus the widening of the pilot hole; characterised in that: it comprises first actuator means which are borne by the main body and which comprise a plurality of hydraulic cylinders (55, 63, 64); it comprises a first plurality of arms which are borne by the main body and which are activatable by the hydraulic cylinders of the plurality of hydraulic cylinders (55, 63, 64) in order each to move between a retracted position and an extended position with a planar movement that is perpendicular to the axis of the main body; each of the first plurality of crushing elements for crushing rock is borne by an arm of the first plurality of arms, is rotatable with respect to the cited arm of the first plurality of arms and is arranged in order to be able to press against, and roll along, the lateral wall of the pilot hole during use of the rock crushing unit, i.e. when the main body is inserted in the pilot hole and is drawn in rotation with respect to the axis thereof and when the hydraulic cylinders of the plurality of hydraulic cylinders (55, 63, 64) activate the first plurality of arms so that they move towards the extended position; the arms of the first plurality of arms are arranged in such a way that when the crushing unit is in use, the reaction forces which are generated on the arms of the first plurality of arms, and which are due to the pressure exerted by the crushing elements of the first plurality of crushing elements on the lateral wall of the pilot hole, compensate one another. it comprises a main body dimensioned so as to insert in a pilot hole realised on rocky terrain and activatable in rotation with respect to the axis thereof; it comprises a first plurality of crushing elements for crushing rock; the rock crushing unit is configured so that when in use, the action exerted by the crushing elements of the first plurality of crushing elements on the lateral wall of the pilot hole determines the crushing of the lateral wall of the pilot hole and thus the widening of the pilot hole; characterised in that: it comprises first actuator means which are borne by the main body and which comprise a plurality of hydraulic cylinders (55, 63, 64); it comprises a first plurality of arms which are borne by the main body and which are activatable by the hydraulic cylinders of the plurality of hydraulic cylinders (55, 63, 64) in order each to move between a retracted position and an extended position with a planar movement that is perpendicular to the axis of the main body; each of the first plurality of crushing elements for crushing rock is borne by an arm of the first plurality of arms, is rotatable with respect to the cited arm of the first plurality of arms and is arranged in order to be able to press against, and roll along, the lateral wall of the pilot hole during use of the rock crushing unit, i.e. when the main body is inserted in the pilot hole and is drawn in rotation with respect to the axis thereof and when the hydraulic cylinders of the plurality of hydraulic cylinders (55, 63, 64) activate the first plurality of arms so that they move towards the extended position; the arms of the first plurality of arms are arranged in such a way that when the crushing unit is in use, the reaction forces which are generated on the arms of the first plurality of arms, and which are due to the pressure exerted by the crushing elements of the first plurality of crushing elements on the lateral wall of the pilot hole, compensate one another. it comprises first actuator means which are borne by the main body and which comprise a plurality of hydraulic cylinders (55, 63, 64); it comprises a first plurality of arms which are borne by the main body and which are activatable by the hydraulic cylinders of the plurality of hydraulic cylinders (55, 63, 64) in order each to move between a retracted position and an extended position with a planar movement that is perpendicular to the axis of the main body; each of the first plurality of crushing elements for crushing rock is borne by an arm of the first plurality of arms, is rotatable with respect to the cited arm of the first plurality of arms and is arranged in order to be able to press against, and roll along, the lateral wall of the pilot hole during use of the rock crushing unit, i.e. when the main body is inserted in the pilot hole and is drawn in rotation with respect to the axis thereof and when the hydraulic cylinders of the plurality of hydraulic cylinders (55, 63, 64) activate the first plurality of arms so that they move towards the extended position; the arms of the first plurality of arms are arranged in such a way that when the crushing unit is in use, the reaction forces which are generated on the arms of the first plurality of arms, and which are due to the pressure exerted by the crushing elements of the first plurality of crushing elements on the lateral wall of the pilot hole, compensate one another.