Diaphragm walls provide rigid, cost effective solutions for permanent retaining walls and shafts, with less construction joints than bored pile walls. They are particularly suitable for large, more open sites where structures greater than 25m deep are required.
The Diaphragm walling technique offers improved verticality tolerances to CFA and rotary bored piling, up to 1:400 for Hydrofraise, and delivers a smoother finish. Water tightness is normally delivered using a CWS water bar between the diaphragm wall panels.
Present day methods of constructing diaphragm walls – by using a bentonite powder mixed with water suspension (slurry) to support and stabilise the trench walls during excavation – have been adapted from the drilling techniques employed by oil well engineers.
We have developed a range of construction techniques and components in this field including CWS watertight seals, rope suspended grabs, KS3000 hydraulic grabs for increased production and verticality control, and Hydrofraise reverse circulation excavation rigs (including compact models). This excavating equipment works quickly and effectively through the viscous slurry whilst maintaining accuracy of alignment both vertically and between panels.
For rock and deep walling applications, Hydrofraise drilling machines are utilised. The use of the Bachy Soletanche patented CWS Stop End incorporating a waterbar, ensures maximum water tightness between adjoining panels.
Diaphragm walls are constructed as permanent walls, which reduces the width of construction and working space required when compared to a solution that has both a temporary ground support and permanent works within.
Walls can be made extremely stiff and therefore better resistant to deflection. It is also possible to use effective internal propping with a diaphragm wall rather than the normal ground anchors. Temporary cut-offs can also be created using this technique.