The elements of a tubular combined wall system are the tubular king piles, C9 connectors and AZ sheet piles. The tubular king piles can be spiral welded or longitudinally welded, and manufactured from a wide range of steel grades, thicknesses and diameters to suit variable design requirements. C9 connectors are welded longitudinally to opposite sides of the tubular king pile to provide the connection point for the infill sheet piles. The AZ sheet piles interlock with the C9 connectors and are driven between tubular king piles as infill sections.
Structurally, the tubular king piles fulfil two functions:
- As retaining members, they resist horizontal loads resulting from earth and hydrostatic pressures
- As bearing piles, they resist vertical superimposed loads.
The intermediate sheet piles have only an earth-retaining and load transfer function and they may be shorter than the king piles.
Features and points for consideration with the tubular combined wall systems are:
- Tubular king piles facilitate the option to drill internally to advance driving in difficult conditions.
- Tubular king piles provide an opportunity to pour concrete inside the king pile creating a composite structure.
- Accurate alignment of the C9 interlock on the external surface of the tubular pile is critical to the successful driving of the infill sheet piles. Grinding of external welds on the tubular pile is necessary to ensure consistent surface profile.
- Control of the tubular king pile alignment during driving will usually result in the guide frame generating forces on the C9 connectors, hence weld quality of the connectors is a critical requirement (Some contractors prefer the HZ/AZ combination which eliminates this issue).