Secant Pile Beam Wet Setting Method

[koverot]

Please excuse me if this in the wrong forum.

I am currently working on my first Secant Piling project. Our deepest piles consist of a 900mm diameter, 20m deep pile, with the male piles having a W610x125 beam for the full depth. Due to the soil conditions we have abandoned CFA and are only using a conventional drilling method. The tolerances on plumbness are very tight, and currently both of our piling subs are having problems meeting it.

Currently we are wet setting our beams and are using a 170mm +/- 30mm slump, 14mm AGG mix with 3 hours delay to allow for max workability. I am querying peoples experience with wetsetting at these depths. I imagine the hydrostatic pressure of the concrete in a confined pile will cause some uplift that will cause the beam to not set straight? Have people used templates successfully?

Really any information to help would be appreciated. We have considered placing the beam first and pouring around the beam, however we feel that as we pull each section of casing it would be difficult to maintain plumbness.

 

[Retrograde]

A few questions:

What soil conditions caused you to abandon CFA.

Why are the tolerances so tight?

Are we talking about the tolerance on the overall wall or the tolerance on the steel beam?

 

[BigHarvey]

Change the piling subs. Apparently they don't master secant piles.

 

[Panars]

How are you measuring the plumbness? At the top or have you already excavated down partway? I would think the plumbness of the hole may be to blame. You can place spacers on the pile to make sure it is in the center of the hole, but that only works if your hole is vertical. For the hole diameter and pile size, you should have 125 mm clearance from the outside edge of the flange. That may not be enough, as the bottom of the hole may be up to 300 to 400 mm off center.

 

[koverot]

Sorry for the delay in response, Ive been away. Thanks for the replies

To Retrograde:

We have a high water table, approx. 2m below grade, with pockets of artesian pressure water with up to 10m above grade head. The ground is mainly sand with some gravels, this combined with intermittent bands of hard rock. The CFA drill rig was just too slow for the conditions and the wear on parts and machinery was huge so we abandoned.

Tolerences are so tight in the Secant piles themselves as we need to ensure overlap to depth to create a watertight barrier. The tolerances on the beam is that we will be chipping away the concrete to weld struts to the beams as we construct the tunnel.


To BigHarvey:

In an ideal world.


To Panars:

THe plumbness of the secant wall is measured by the drill rig. The plumbness of the steel is directed by a template and plumblines, and surveyed at completion vs control points.

Does anyone have a suggestion on the best methodology for installing the steel. Anyone have experience with placing the steel and pouring around. Due to the soil conditions we would have to support the steel from sinking while the concrete sets which freezes equipment

 

[Retrograde]

I have seen guides used for the placement of steel sections into piles. This is probably overkill:

http://www.skanska.co.uk/Global/Sevices/Piling/Datasheets/Cemloc-for-Embedded-Columns.pdf

But similar systems can be used.