Concreting the slot wall element

The slot wall element is concreted by the so-called contractor method. This is understood as a method for the installation of concrete-supporting liquid. In the raised slot, a concreting tube, eg, sealed by a rubber bell, is also suspended in the case of longer slot wall lamellae, and also two mixing tubes, with an upper charging funnel. During concreting, the lower edge of the concreting tube must be below the surface of the concrete at least by a dimension equal to the length of the lamella or equal to the lamella length or equal to the distance of the concreting tubes. The concrete column in the pipe must not be torn off and the supporting liquid must not penetrate into the pipe. It should be concreted as fast as possible (climb rate greater than or equal to 3 m / hour). If the concrete piles are pulled too hastily and the necessary binding depth does not exist in the fresh concrete, bentonite inclusions can occur in the concrete. The concrete has a spread of 55 cm to 60 cm. In order to prevent demixing, a minimum of 350 kg cement / m³ of concrete, or even a tray or fly ash, must be added.

The bentonite suspension, displaced by concrete, is either directly reused during the excavation of the following slit wall lamella or, for example, when it has been strongly enriched with sand, is first cleaned (by vibrating sieves and by cyclones) and then regenerated Suspension or with a controllably added quantity of water. The suspension can be reused as often as desired, as long as its properties meet the requirements.

As soon as the concrete has reached a certain stiffness, the pipe must be pulled. The semi-circular joints between the individual slit wall lamellae are formed by the shroud. These half-bored joints give a good lateral guidance to the slot wall gripper during the dredging of the next slot. Pulling the cut-off pipes is carried out either by the excavator or, as the adhesive forces between the casing and the hardening concrete are quite large, as a rule by hydraulic pressing.

The concrete of the finished wall may only be regarded statically as B 25 in order to avoid a too high reinforcement percentage. The top zone (0.5 m to 1 m) of the finished wall can be permeated with bentonite and sand and must be caulked when components are connected here. The filter cake (bentonite / cement / soil mixture) on the inside of the wall should be removed by castering after the excavation excavation, if a plaster for the sealing underlay is applied to the diaphragm wall.