Tie rod site assembly & installation
Typically anchor bars are installed whilst being supported at the design level, if the design of the wall allows it, the fill can be made to the correct, or near to the correct anchor level, which greatly assists installation. Once connected any slack in the anchor is taken out via a turnbuckle or a nut at one end of the anchor. Anchors only provide restraint to the structure if in tension therefore it is vital that all slack is removed from the system. Using human force alone it is not possible to induce more than a nominal tension in the anchor, but this is generally sufficient provided the tie bar is installed in a straight line between the front wall and the anchorage.
For larger diameter tie bars removal of slack is most easily achieved at a threaded end of the tie bar by means of a hydraulic cylinder, typically a load of between 30-60kN is required and this can either be left in the tie bar by tightening the load nut before release of the load or the load released and the load nut hand tightened. Consideration to the practicality of this should be made at design stage, in particular checks to the stability of the wall during construction phase.
Sheet pile tie rod installation sequence
The following is a recommended sequence of events to ensure that the anchors are installed and tensioned correctly.
- Backfill to approximately 150mm below the finished level for the ties
- Place sand bags every 6m along the shaft or on either side of coupler/turnbuckle or articulated joint to support the anchor to the required level. If settlement ducts are not being used consider supporting the bar to a higher level than design to allow for anticipated settlement (note articulation joints are recommended).
- If required fit settlement ducts
- Check that each connection is soundly made. Threaded connections require at least 1 x Thread Outer Diameter for minimum engagement (check with manufacturers literature)
- Tension the anchor either using a turnbuckle or with a nut on the outside of the wall/anchorage
- Compact sand around the full length of anchor
- Backfill to required level
This procedure applies to a simple situation and additional activities may be considered, for example using a hollow ram jack to apply a pre-tension before final backfill or stressing after backfilling to prevent future movement due to subsequent loading.
Further information on stressing is available on request from our technical department.