A Combi-Wall is a combination of sheet piles and pipe piles. The pipe piles resist the overturning pressure of the soil and the steel sheet piles are cost-effective in-fill between the pipes. These types of walls can be either permanent or temporary, in which case the steel can be extracted and re-used.
The pipe pile portion of a Combi-Wall is normally a drilled caisson and may be concrete filled and reinforced if the wall is to be permanent. The pipe has interlocks welded on each side and a sheet pile filler is installed in between the pipe piles. Installation of the sheet piles is normally accomplished by vibratory hammer while the pipe piles are usually drilled. These are the most common techniques, but other configurations such as h-piles are also possible.
Combi-Walls are a cheaper alternative to a full caisson or secant wall where a sheet pile wall isn't sufficient. They are particularly effective in temporary cofferdams since the steel can be removed and re-used once the structure is no longer needed.
Bermingham has installed a number of these structures in the past years, including a dock extension at the Oshawa Harbour and a temporary cofferdam for the replacement of a dam on the Trent-Severn waterway. Video of both of these project can be seen on the media page.