Off-centre anchoring of AZ sheet pile walls

Off-centre Anchoring of AZ Sheet Pile Walls: An Economical and Effective Tie Back Solution

The Z-section sheet piles of the AZ series marketed by Arcelor Profil Luxembourg differ from the Z-section sheet piles of competitors and from U-section sheet piles in the following ways: 

  • the combination of the advantageous Z profile and the time-proven Larssen interlock make them an economical solution with a superior section modulus- to-weight ratio; 
  • the favorable position of interlocks on the outer side, on the extreme fibre, overcomes the problem of transmission of shear force in the interlock, making crimping unnecessary to guarantee maximum strength.

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In practice, however, when sheet piles are to be tied back, it is not uncommon for U-section piles to be preferred. This choice is made for detailing reasons: with U-section sheet piles both waling bolts and tie rods can be centred on the back of the pile.

If Z-section piles are used, the interlock running down the centre of the trough results in conservative measures being adopted, with walings being fixed with two bolts, thereby increasing material costs and the complexity – and cost – of installation. 

If tie rods are to be centred on the trough, they have to pass through the interlock. This requires a special bearing plate with welded shims to bridge the interlock ridge. If the water table behind the sheet piles reaches the line of tie rods, the hole through the interlock might impair watertightness.

An economical solution for anchoring AZ piles 

To enable full advantage to be taken of the AZ series sheet piles under the most economical global conditions, Arcelor Profil Luxembourg has developed a financially attractive alternative solution: 

off-centre anchoring. 

This solution combines the outstanding static properties of AZ sheet piles with the simplicity of the anchorages used with U piles. It simply involves putting the bolts or tie rods through one of the flanges alongside the interlock: this avoids the problem of making a hole through the interlock and using a complex bearing plate.

The advantage of off-centre anchoring is that it mobilizes the high strength of Z piles without having a hole through the interlock. 

The economic advantages are obvious: 

  • off-centre fixing of walings with a single bolt reduces material and installation costs, 
  • off-centre positioning of tie rods makes it possible to use plain bearing plates, and having a hole in the flange rather than through the interlock means achieving effective waterproofing ceases to be a problem.