Apparatus for injecting cement mortar into earth layer

A unit for injecting laitance into an earth layer and having an injection member which is rotatably mounted on a triple-walled pipe. The unit has an injection nozzle 64, which is mounted in a side wall part in the unit having outer and inner concentric discharge openings 62, 60 connected respectively to a compressed air passage 56 and a high-pressure water passage 58. For the injection of laitance there is a nozzle 68, which is arranged in the foremost part of a side wall part and is detachably fastened thereto, the discharge opening of which nozzle is connected to the laitance passage 54. Between the two said nozzles is arranged a partition wall part 65, which is removable and which, when replaced by another wall part, allows an adjustment, dependent on the nature of the earth layer, of the vertical spacing L between the two nozzles. The nozzles are placed at a right angle relative to the axis of the unit in order to lead off fluid in the radial direction and are arranged in the unit such that the fluid reaction forces substantially cancel each other out.