Abstract: In tunnel construction with shield drive locational concrete is brought in stages directly behind the shield as tunnel lining. In order not to have to interrupt the shield progress during concreting it is proposed to provide a shield tail element consisting of a plurality of lamina movable relative to the shield, in addition to a shield tail element attached rigidly to the shield. This basically stands still during the continuous progress of the shield and is drawn forward into the shield by lamina only during the segment concreting, in order to remain immobile there relative to the earth until the next concreting stage.

Abstract: A sewage ventilating basin of a sewage treatment plant comprises a sewage container which is sunk into the ground and into which project three vertical tubes which connect the surface water of the container with the deepest water thereof. By means of feed pumps, a downwardly-directed flow is produced in the tubes so that the sewage in the container circulates upwardly and recirculates in the tubes. Disposed in each tube in the upper part thereof are devices for the fine-bubble introduction of a ventilating gas. The flow velocity of the sewage in the tube and directly below this upper part is higher than the uplift velocity of the gas bubbles being introduced into the flow at the same point. Since the gas is introduced into the sewage not in the bottom zone of the container but instead in the upper part of the tube, the gas pressure is lower than in the case of the direct introduction of the gas into the bottom zone, and also the energy expenditure is smaller with a high effectiveness of the ventilation.