already displaced radially outward and compacted this compaction is continued by the rear drill head element 9 whose sheath surface is configured conical in its front section and whose diameter widens to a diameter viewed from front to back which corresponds to the one of the housing 3 of the ground rocket in contrast to the step drill head known form the state of the art the instant drill head which has a plurality of radially extending cutting elements 11 which already substantially correspond to the final diameter of the bore allows achieving a particularly high directional stability of the ground rocket during its movement in the ground of course it is also possible to use the ground drilling device according to the invention with any other drill head such as for example with a conventional step drill head the support of the impact bolt 5 in the basic body 1 is provided inter alia by the threaded ring 13 which is screwed into the front end of the housing 3 for this the threaded ring 13 has an outer threading and the housing has a corresponding inner threading adjoining the rear end of the threaded ring 13 is a threaded bushing 14 which also has an outer threading which engages in a corresponding inner threaded of the housing 3 a ring shaped space is formed between the threaded bushing 14 and the corresponding section of the impact bolt 5 in which space a cylindrical 15 is arranged this helical spring 15 is supported on its front side on a projection of the threaded bushing 14 and on its rear side on a projection of the impact bolt 5 as soon as the impact piston 4 impacts the rear end of the impact bolt 5.