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Diaphragm walls

Application.

Cast-in-place concrete diaphragm walls are used if only minor deformations can be permitted due to existing building developments, and the excavation base lies below the existing groundwater level.

As solid excavation pit installations, diaphragm walls can be executed very close to existing building developments. In addition, they offer the possibility to adsorb permanent loads as supporting structures.

Manufacture.

The execution takes place low-noise and vibration-free in so-called two-phase procedures. During manufacture, individual slats are lifted out with grabs. Guide walls are constructed at the top ground surface in order to guide the excavation tool and to secure the adjacent ground.

At greater depths, the earth walls are secured against collapsing through the supporting fluid bentonite slurry. In order to seal off the excavation pit horizontally against the groundwater, the diaphragm walls incorporate adjacent soil layers with lower water permeability or artificially manufactured sealing bases.

After achieving the planned slot depth, a reinforcing cage in a length suitable for the statics is suspended in the support fluid. The concreting of the slats takes place using the Tremie method (from bottom to top) whilst simultaneously pumping off the support liquid.

Tight joints.

The individual slats are separated during excavation by water stops or stop end elements. When using FRANKI water stops, two sealing tapes can be installed in order to additionally seal the joint between the individual slats.

Quality assurance.

The movements of the diaphragm wall grabs are monitored through inclinometers and are electronically recorded. The finished diaphragm wall can also be inspected later through inclinometer measurements for deformations during the anchoring and excavation work.

Umweltfreundlichkeit.

Zum nachhaltigen Bauen gehört auch die Schonung von Ressourcen wie z.B. Kies für den Beton einer Schlitzwand. Bereits 2013 erstellte FRANKI eine Schlitzwand unter Verwendung von ressourcenschonendem Beton, d.h. Beton mit recycelten Gesteinskörnungen (kurz RC-Beton).

Es handelte sich hierbei um die Baugrube für den Neubau des Forschungs- und Laborgebäudes für Lebenswissenschaften der Humboldt-Universität zu Berlin. Dieses „Pilotprojekt“ wurde von der Berliner Senatsverwaltung für Stadtentwicklung und Umwelt ins Leben gerufen. Die Fachgruppe Bauliches Recycling der BTU Cottbus – Senftenberg wurde mit der wissenschaftlichen Begleitung der Baumaßnahme beauftragt. FRANKI verbaute rund 1.700 m³ RC-Beton in der Festigkeitsklasse C25/30 und Expositionsklasse XA1, XC4. Dabei konnten ca. 25 Vol.-% Kies substituiert werden.

Durch den erstmals in Berlin eingesetzten RC-Beton wurde ein nachhaltiger Beitrag für den Ressourcenschutz geleistet. So konnte eine Flächeninanspruchnahme durch Kiesabbau vermieden sowie eine Verringerung der Umweltbelastung durch Transport und Herstellung der RC-Gesteinskörnung erreicht werden.

Quelle: https://www.umweltbundesamt.de/themen/wirtschaft-konsum/umweltfreundliche-beschaffung/gute-praxisbeispiele/gebaeudeneubau/berlin-einsatz-von-recycling-beton-im-hochbau

Wirtschaftlichkeit.

Aufgrund der höheren Kosten für die Baustelleneinrichtung ist die Schlitzwand ab einer Mindestgröße von ca. 2.000 m² wirtschaftlich sinnvoll. 

Geothermal technology.

In the case of cast-in-place concrete diaphragm walls, it is also possible to use them as geothermal elements. For this purpose, appropriate lines are installed for the utilisation of geothermal energy to heat and cool buildings.

Barrettes as a foundation element.

Barrettes are a special form of diaphragm wall which are used for foundations. They can be designed as rectangular individual elements as well as cross, T or L-shaped elements. The applied loads are transferred via the point bearing pressure and skin friction.

The use of barrettes instead of large bored piles is expedient if for example an excavation pit enclosure is conducted using a diaphragm wall, and the construction site equipment and machinery is already on the construction site.

Measurement.

The manufacture of diaphragm walls takes place in accordance with DIN 4126 or DIN EN 1538 as well as the recommendations by the Excavation Pit Working Group (EAB). We execute diaphragm walls in wall thicknesses of 45–150 cm.