Brochure 26-01E

Diaphragm walls and barrettes

Diaphragm walls to stabilise deep excavations and as deep foundation elements.

Stabilisation of deep excavations and deep foundationsDiaphragm walls are supporting walls, which are concreted as so-called “lamellae” in narrow, deep trenches.Diaphragm-wall lamellae are excavated with rope grabs or trench cutters with special shovels adapted to the in-situ soil. A supporting slurry with special thixotropic properties stabilises the lamella during the excavation work. Then the pre-assembled reinforcement cage is installed using a suitable lifting device. The lamella is concreted with tremie pipes. In the course of concreting, the slurry is pumped out and regenerated.The reinforced-concrete wall thus built fulfils two functions: It acts as a permanent, watertight supporting wall and as a deep foundation element for the building to be erected.The diaphragm wall can be constructed as a self-supporting wall, or it may require single or multiple bracing or anchoring. Individual diaphragm-wall lamellae, known as barrettes, or a combination of lamellae can be used in large-scale deep foundations designed to support very high loads.Other applications of diaphragm walls include shielding walls and cut-off walls.

Advantages of diaphragm walls:

• diaphragm walls can be constructed in a very wide range of soil types,

• fast execution,

• optimised construction costs, since the same element can be used as a supporting wall, a cut-off wall and a deep foundation element,

• construction is possible close to existing buildings (a clearance of about 30 cm from the outer walls of buildings must be observed),

• low environmental impact during the works – only moderate noise, no vibration during construction,

• able to take very high vertical and horizontal loads and bending moments,

• can be used as top-down method in order to optimize the sequence of operations to be performed in inner-city areas.

Diaphragm wall secured with partial cover around perimeter

Braced diaphragm wall

Diaphragm walls and barrettes

Construction steps

Preparation of the joint elements

Concreting of diaphragm-wall

Installation of reinforcement cage

Excavation of diaphragm-wall

Rope grab1 Construction of the guide walls

Guide walls are built of reinforced concrete and fulfil the following functions:

• they stabilise the upper part of the diaphragm-wall,

• they reflect the geometry of the diaphragm walls and they ensure their verticality (they guide the grab during excavation),

• they function as a bearing for extraction forces when recoverable joints are used,

• they enable the required level of supporting slurry to be maintained to stabilise the open trench.

2 Preparation of the supporting slurry

Diaphragm walls are stabilised by the hydrostatic pressure exerted by the supporting slurry on the trench walls, and by the ingress of the slurry into the soil (filter cake). The materials used in the slurry are usually based on bentonites or specific polymers.

3 Excavation of diaphragm-wall lamellae

In plan view, diaphragm walls are divided into primary and secondary lamellae. The design length of the lamellae is generally between 3 and 6 m; under certain circumstances, however, it can be up to 10 m.

4 Installation of reinforcement cages

The reinforcement of a single lamella can consist of several reinforcement cages. Care is taken that the reinforcement of the lamellae at any single point is not excessively dense, in order to ensure the necessary flow of concrete through the reinforcement. The reinforcement cages are positioned using special cranes, or on small building sites with the excavator.

5 Concreting of lamellae

The lamella is concreted immediately after the reinforcement cage is inserted. The concreting is performed without interruption. The displaced supporting slurry is pumped into a special storage facility where it is regenerated for further use. To ensure a watertight seal between adjacent lamellae, specially designed seals are used for the joints between the lamellae.

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Application examples

Construction site Patio Verde in Chambéry (France)

Tunnel under the Vistula, Danzig (Poland)

Residential complex in Moscow (Russia)

� Inner-city excavation, turnkey project (diaphragm wall, injection works, excavation, struts)

� 20.5 m-deep inner-city excavation as target shaft for tunnel-boring machine and as a seal block, realised by jet-grouting

� 20 m-deep diaphragm wall, wall area 16,800 m2, for the construction of the real-estate project "Donskoy Olymp" in Moscow

Keller Group plcGround Engineering Contractorswww.keller.co.uk

Keller Holding GmbHwww.kellerholding.com

EuropeKeller Grundbau GmbHKaiserleistrasse 863067 OffenbachGermanywww.kellergrundbau.de

Keller Fondations Spéciales2 rue Denis Papin - CS 69224 Duttlenheim67129 Molsheim CedexFrancewww.keller-france.com

Keller Grundbau Ges.mbHMariahilfer Strasse 127a1150 ViennaAustriawww.kellergrundbau.at

Keller UKOxford Road · Ryton-on-DunsmoreCoventry CV8 3EGUnited Kingdomwww.keller-uk.com

Keller Polska Sp. z o.o.ul. Poznańska 17205-850 Ożarów Mazowiecki (Warsaw)Polandwww.keller.com.pl

Keller Cimentaciones, S.L.U.Miguel Yuste 45, bisE28037 MadridSpainwww.keller-cimentaciones.com

Middle EastKeller Grundbau GmbHDubai BranchOffice No. 408Al Mansour Building Damascus Street, Al QusaisDubai, UAEwww.kellerme.com

AfricaFranki Africa674 Pretoria Main Road,Wynberg, 2090 SandtonP.O. Box 39075, Bramley, 2018 South Africawww.franki.co.za

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