The first phase is to install a working platform and construct a guide wall. Diaphragm wall cutters are usually purpose-built mechanical or hydraulic grabs, suspended from a crane or crawler-mounted rig. Where diaphragm walls are exceptionally deep, or in hard ground or rock, milling machines (hydromills) can be used. Great accuracy can be achieved as grabs and mills are ‘steerable’, within limits.
During excavation, drilling fluid, usually a bentonite suspension is used to ensure the cavity remains stable and stands open. ‘Stop ends’ are installed and a pre-made reinforcement cage installed. Concrete is then tremmied into place and the bentonite recovered for cleaning and re-use. The rig will then move around five panels away and start again. An abutting panel is only completed when the concrete in the first has gained sufficient strength.
‘Top down’ construction techniques
Diaphragm walls are particularly suited to the construction of very deep retaining walls and often seen together with ‘top down’ construction techniques. These allow building work to take place above ground, while deep excavation work continues at the same time.
Diaphragm walls generally provide a high level of leak protection to deep foundations.
Cementation Skanska has carried out major diaphragm wall projects on landmark infrastructure projects, such as Heathrow Airport and Nine Elms Northern Line Extension.
The UK’s first Energy Wall™
We used our combined expertise on geothermal energy and diaphragm walls for the Bulgari Hotel in Knightsbridge, where we installed the first Energy Wall™ in the UK.