The installation method of soil displacement using an impact mole is generally employed for installation of building service connections. A pneumatically operated hammer drives open a cavity (the “bore”), in which the new pipe is then embedded. The soil must be displaceable to permit this. Static support of the impact mole is necessary in loose and soft soils, since otherwise it is not possible to achieve sufficient friction with the soil for independent advance. The shape of the bore is thus more accurate in stony soils, as a result of lateral displacement of the stones. Transverse deflection of the impact mole occurs to a limited extent. Orientational sighting of the target point is performed in the starting pit. Pipes of up to OD 200 mm can be installed using this method.
The effective service-life of the newly installed pipe depends on its degree of damage. Damage levels of up to 10 % of pipe wall thickness can be tolerated by the material, whereas scratching and scoring beyond this reduce the service-life of the supply pipe. For this reason, the use of sheathed pipes is also recommended in DVGW Code GW 321.