What is Slurry Wall? What is the Function of Bentonite there?

Slurry wall technique is used to build water blocking diaphragm walls surrounding open cuts and tunnels and to facilitate laying foundation. Generally reinforced concrete walls are constructed in this technique. This technique is very useful in areas where walls are surrounded by soft earth near open water or high ground water is available around construction site. This technique was successfully used in construction of bathtub surrounding world trade center construction site. 
For each desired wall a trench is excavated. This trench is filled with thick colloidal mixture of Bentonite and water and this colloidal mixture is kept constant in this trench. This slurry produces a pressure that counteract the hydraulic pressure from surrounding soil that would try to collapse the trench resulting many inconvenience to construction process.
The later processes of regular reinforced concrete work like rebar assembling and formwork for concreting are performed in the trench that is filled with bentonite slurry. Now question is how concrete is poured in the trench that is filled with bentonite slurry? Try to understand how piling work is done. 
 Excavation of trench for slurry wall filled with bentonite to avoid collapse
There also concreting is done within water and bentonite slurry. The bentonite slurry is lighter than liquid concrete and easily displaced by concrete. As concreting process goes up the displaced bentonite also goes up and this overflowed bentonite is then collected or transferred to another trench to facilitate another wall construction without collapsing surrounding soil.

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