Using a rock crushing system for widening a pilot hole on rocky terrain includes taking a plurality of crushing elements, for example roller bits and/or cutter discs, pressing the crushing elements against the lateral wall of the pilot hole and at the same time rolling the crushing elements along a cylindrical portion of the lateral wall, widening the pilot hole. The crushing elements, free to rotate with respect to an axis thereof, are radially pushed by hydraulic cylinders. Stabilising means exemplarily include a basket abutting the lateral wall to keep a main body bearing the hydraulic cylinders centered with respect to an axis of the pilot hole during the rock crushing.