Temporary Retaining Walls

Hi Everyone,

We plan to start our new build in the coming months and I'm currently in the process of reviewing the engineering and would appreciate some feedback on temporary retaining walls to support excavation. The current engineering plans specify the 9 x 450mm soldier piers with N12 cages positioned on the boundary. Note:

- Excavation depth (site cut only) varies between 1,800mm on the left to 1,200mm on the right side due to our sloped block.
- Footings are a further 600mm deep (min).



I have received conflicting information from builders on the cost of these piers. One has said approx $500ea, the other approx $1000 each and I am also waiting for a quote myself. What price should I be expecting for these?

In either case, given these piers will only be used to support excavation I would ideally like to remove them all together (unlikely given the house wall is 1,000mm from the boundary) or use a temporary method such as sheet piles or an alternative.

I've looked everywhere but haven't been able to find an indicative cost for sheet piles. Based on peoples experience are sheet piles a cost effective solution?

Also, are there any alternatives such as screw piles I should be considering?

The soil report mentions vertical excavation should remain unsupported for a maximum of a few days therefore I'm thinking it may be possible to complete the excavation, build a traditional sleeper wall and later remove this when the core-filled brick wall is completed. Does anyone know if this is a feasible solution?

Thanks in advance.

Hi Chops
Welcome to the forum
Permanent piling(lysaght) or removable shoring/proping of formwork or engineered sandwich bondek (lysaght) concrete filled are all options but more info is required ie soil types, accessibility, what's adjacent to the boundary next door,etc,.etc Also photos do help

Thanks for the welcome and reply

Below is some additional information;

Accessibility isn't an issue as we are on a corner site without any vegetation or obstructions as shown below. The location of the required excavation (approx 7m long) is marked with a red line. Although it's not entirely clear in the Google Map picture, the adjoining area is the neighbours concrete path. We will also be excavating towards the front of the property parallel to the neighbours garage, however we are 3m off the boundary at this point and will batter at 45deg without piers as recommended.



The site is classified as Class M and the soil composition in the area marked above is as follows:

Hi Chops
Thanks for the info, just a couple of points
Google maps lacks details, topo/contours, sometimes a closer photos down the boundary are equally helpful. The test/trail pits and bearing capacities are used to determine the pile/footing depths. What stage are you at have you sign the building contracts yet and whose decision was it to do the footing and pile retaining that way?
I always suggest that clients get preliminary engineering options before hand reason being the quotes for such works will always be cheaper before than later when you have partialy committed and given a deposit..as there is no incentive for them to sharpen their pencil on the quote
You can leave a PM if you wish

We are still discussing the project with builders so no contracts have been signed as yet. In either case, we only need a builder to oversee the project until lock-up at which point we will take over and complete the fit-out. If that doesn't work out then I'm more than happy to complete the entire project as an owner builder.

The structural engineer decided to retain in this manner and overall I'm quite pleased with their work and ongoing support - definitely one of the better engineering firms we've worked with. We spent quite a bit of time discussing the entire project in detail (ICF basement walls vs core filled brick, suspended slabs vs posi floors, frame sizing, steels, shotcreting etc) before the detailed engineering work was completed.

I just don't like the idea of literally sinking thousands of dollars into piers that are non value adding. Once the walls are completed they will serve no purpose, hence my question on temporary walls and other suitable alternatives. Our engineer has already advised that soldier piers as designed are the most cost effective solution, however I'd like to understand the alternatives along with some objective data so I can make a final decision and move forward.

Thanks for the additional information? I assumed you had signed a building contract and you were left to deal with the builders design/retaining? In which case the Builder has a preference to a particular solution because their strengths/trades lie in that area..it may not be the most economical but boosts his overall profit.
I find engineers think out side of the box for solutions but finding trades to think in similar relative cost savings is difficult.Hence the reason I work along the entire build chain.
Originally I though we were dealing with footings? Constructing basements may or may not require temporary retaining walls.
You have probably looked at these solutions but i will mentioned this for others
For eg. Alternatively, on (or near) Boundaries we use sheet piling (see below my G+ for iso 3D detail/engineering/construction ) or deep concrete footings various waterproofing systems (costly) & drainage cavities can be used on the inside walls.
$500 for a (obsolete) pile is a fair price ..

If $500 per pile is a fair price then I assume $1,000 per pile is a little too steep? What is a realistic price for sheet piling, both temporary and permanent?

All things being equal I would say Yes

Contact your state suppliers they should give you prices & contractors details.
From my experience they are priced similar by many?
I wouldn't recommend temporary piling the costs & difficulty of removal are the main considerations against.
The savings is in offsetting part of the cost with another part of the basement element

I had a quick look at the last project we did with piling the cost then was $900 p/m.
BTW lysaght no longer has piling... its now imported from china.