Soldier Pile Walls - Australian Practice (Melbourne)

[GeotechNerd86]

I am writing this thread from Africa and have seen that Multi-anchored Soldier Piles (Concrete and shotcrete lagging) are used extensively in places such as Melbourne.

I have a few questions and was hoping someone from there would be so kind to respond:

- AS4678 does not provide clarification on how you should look at the required anchor forces (Assuming we are using LE methods). Do you use equivalent earth pressures(Terzaghi and Peck or FHWA?) and specify anchors with similar tieback forces and structural capacity with increase in depth? I assume this is then checked in FE or with Beam on Elastic Methods to confirm the requirement?
- Do you use equivalent earth pressures to derived Bending Moments in the piles or other methods? And then check these in FE or BOE?
- Do you use post injection grouting to increase the bond strength of the ground anchors?
- I see you also leave gaps in your shotcrete lagging, why don't you just but the permanent slabs up against the wall? What is the reasoning behind tieing the slab to the wall?
- Do you have high ground watertables and do you dewater site or wont you use Soldier Piles in such cases?
- Why the need for a capping beam before you excavate? We normally only construct this once we reach the ground slab?

Thanks so much

GeotechNerd

 

[Retrograde]

Generally I would use software like WALLAP to calculate the anchor forces and pile bending moments.

We would dewater the site if feasible but it depends a lot on the ground conditions. With a high water table in sands we would probably use a secant pile wall.

I've seen the capping beam done both ways. But installing it before the dig gives the wall more robustness in case of an anchor failure. Also, walls are often braced at capping beam level with props rather than using ground anchors.

 

[yakpol]

Here's the structural engineer take on soldier pile wall design in AU:
- the walls will be analyzed using software capable to perform staged analysis, such as FREW, WALLAP or Plaxis, which will calculate earth pressures and pile/tieback forces. FHWA final earth pressure diagrams typically are not used even for preliminary design.
- pressure grouting of anchors will be used to decrease the bonding length
- shotcrete lagging is economical and therefore preferable, allows fast excavation. It will be used if soil standup time and ground water conditions allow. Fascia wall will be built later. Different methods will be used in more difficult conditions, like ground water in non-cohesive soils.
- It's easy to construct capping beam on grade rather than using falsework (at least on excavated side). Also, it ensures that piles deflect together and share loads while excavation could be quite uneven.

I may missed a bunch of valid points, it's been 10 years ago when I worked in AU.

Regards,