Strutting your stuff

GROUND The first struts are installed as excavations continue.
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Piled Wall

While this project is very interesting, there are other methods of building that should be taken into consideration. One of these is piled walls. These methods of retaining wall construction employ bored piling techniques – normally with the continuous flight auger method (CFA) or rotary. They provide special advantages where available working space dictates that basement excavation faces be vertical.

 Both methods offer technically effective and cost efficient temporary or permanent means of retaining the sides of bulk excavations even in water bearing strata. When used in permanent works, these walls can be designed to accommodate vertical loads in addition to movements and horizontal forces.

Construction of both methods is the same as for foundation bearing piles. Contiguous walls are constructed with small gaps between adjacent piles. The size of this space is determined by the nature of the soils.

Secant piled walls are constructed such that space is left between alternate ‘female’ piles for the subsequent construction of ‘male’ piles. Construction of ‘male’ piles involves boring through the concrete in the ‘female’ piles in order to key ‘male’ piles between them. The male pile is the one where steel reinforcement cages are installed, though in some cases the female piles are also reinforced.

All types of wall can be constructed as free standing cantilevers, or may be propped if space and sub-structure design permit. Where party wall agreements allow, ground anchors can be used as tie backs.

Rotary boring techniques offer larger diameter piles than any other piling method and permit pile construction through particularly dense or hard strata. Construction methods depend on the geology of the site. In particular, whether boring is to be undertaken in ‘dry’ ground conditions or through wet but stable ones.

Upon reaching the design depth, a reinforcing cage is introduced, concrete is poured in the bore and brought up to the required level. 

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Back at the bank site, like most projects, this one was on a very tight schedule, and the crews had to work all shifts to ensure it was delivered on time. However, it was, in spite of the amount of technical challenges and paperwork common to all early stages of building.

Support

Of course, there have been revisions, as Saliby illustrated: “On this particular project, after we designed the system, there was a revision to the elevation to the concrete slab.

"After the first floor slab, the level coincided with the level of the strut at the bottom. 

"This was a problem, so we had to install these inclined struts (at the bottom) so we had to provide these inclines twice in order to remove them. This was not part of the original design, but sometimes there are changes.”

With the foundations now complete, and Edrafor moving on to other projects, we look forward to seeing the bank rise out of the ground soon.

Every geotechnical company needs pile boring machines, and Edrafor has a fleet of 16.

Over the years, the firm has bought equipment from the likes of Bauer, Casagrande and IHC. However, service is equally as important. George Saliby says: “When you are spending hundreds of thousands of dollars on such equipment, the support the company provides is vital. You need people with the equipment and the parts on hand.”

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