A combi wall is an earth-retaining structure consisting of heavy steel tubular piles with sheet piles installed between them.
How does a combi wall work?
A combi wall combines the structural strength of large-diameter tubular piles with the sealing capacity of interlocking sheet piles. The tubular piles — often filled with reinforced concrete after driving — serve as the primary load-bearing elements. Between them, lighter sheet pile sections are threaded into guide slots welded onto the tubes. This hybrid arrangement creates a continuous retaining wall that can resist high lateral earth and water pressures while remaining relatively economical in its use of steel.
The tubes are typically driven first using vibratory or impact hammers. Once the primary piles are in position, the intermediate sheet piles are installed to close the gaps. Depending on design requirements, tie-back anchors or waling beams may be added to provide additional lateral support.
Applications
Combi walls are widely used in civil engineering projects where deep excavations or waterfront structures demand high bending resistance:
- Quay walls and harbour structures — withstanding vessel mooring forces and tidal loads.
- Deep basement excavations — retaining soil in urban environments where space is limited.
- Lock and canal walls — managing differential water levels.
- Bridge abutments — providing stable earth retention adjacent to waterways.
Because the tubular piles can be manufactured in large diameters (up to 2 metres or more), combi walls achieve greater section modulus values than conventional sheet pile walls, making them suitable for depths exceeding 20 metres.
Related terms
- Steel
- Foundation
- Reinforcement
- Concrete
- Construction
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