Piling through revetment quarry run

[charnott]

Concept design is for a secant piled wall to construct a seawater intake structure on an offshore reclaimed island. bored cast in situ piling is prevalent in the region and more importantly the equipment is available at the remote site.

Contractor is unable at this time to provide a detailed methodology for how he will cast the piles in the area of the island revetments consisting of armour rock underlain by quarry run cobble-boulders.

His latest proposal is to insert a geomembrane inside the temporary casing before pulling the casing. I cant find anyone who has come across this approach and am asking the contractor for detailed MS and case histories. I wondered if any peers on here had experience of this or had alternative approaches.

We have constructed steel tube grouted piles for bridge foundations elsewhere on the island however this required specialist equipment and wouldn't be suitable where we're looking to construct the secant pile wall.

TIA

 

[aeoliantexan]

I once saw a presentation by a team that cast piers in a geomembrane sleeve to protect them from contamination in the ground. I believe it was in the Houston area. It apparently worked OK. I am guessing the soils were clays and fine sands.

 

[charnott]

the issue here is more a lack of confinement. Contractors current proposal seems to rely upon the geomembrane providing all confinement to pile concrete as quarry run and armour will provide little to none once the temporary boring casing is withdrawn.

I've called the contractors sub-contractor to explain in detail this week.

 

[hokie66]

I think drilling in that stuff will be very difficult. But once the concrete is cast, it will confine the material and prevent intrusion into the plastic concrete. Not sure what the geofabric is about, but I wouldn't want to have to install it.

 

[BigHarvey]

It will not work : the only way to drill these piles is to use an overburden drilling method (down the hole hammer with eccentric bit and simultaneous casing).

 

[charnott]

Thanks for the replies. The issue at hand has been missed somewhat, likely due to my explanation!

We have already drilled through revetment elsewhere, using bauer spezialtiefbau piling equipment however this work was installing steel column grouted piles. Obviously the steel column also acts as casing to retain the grout during casting.

However to install a secant pile wall we cannot use steel column piles as the boring of the secondary pile has to reem out the overlap with the primary piles. Therefore without the steel column acting as sacrificial casing how are we to bore and then cast the pile.

Bored cast in situ piles are usually cased through superficial deposits but the casing withdrawn almost immediately after concrete pouring, in our scenario that would allow the concrete to flow out through the quarry run. The current proposal is to line the temporary casing with a membrane to retain the concrete once the temp. casing is lifted, something I nor my colleagues have come across or like the sound of.......

hope that clarifies for those kind enough to be participating

TIA

 

[BigH]

A bit off the OP, but when I attended a conference years ago, one chap was talking about driving piles through a cobble/gravel material which would, as one expects, be difficult. They ended up drilling down a small pilot hole, placing charges and blasting the cobbles/gravel which broke up into smaller sizes that they could drive through.

 

[BigHarvey]

I really doubt that you drill easily through armour rock in rotation with a Bauer rig ! Are you sure the other piles were drilled in the same conditions ?
Now if you drilling problem is solved, and I'm far from being convinced, limiting the overbreak can be achieved with pre-grouting ( rigidify the grout with sodium silicate to limit the quantities) or use a thin wall lost tube like COFRATOL )
With a geotextile you can't guarantee there won't be any necking in the pile.

 

[cvg]

well the entire thickness of the revetment core and armor couldnt possibly be more than just a few meters and assuming this is nearshore, than at the SWL. So it seems like the majority of the pile is through either dredged sand or natural sea bottom material. How porous is the quarry run? is it mixed with sand?

 

[aeoliantexan]

My point was just that they seemed to be successful in pulling the casing and leaving the sleeve in place.

I have no applicable experience, but it seems that you just need to know how strong the geotextile must be to contain the concrete across the biggest voids. You can estimate the void size as some fraction of the rock size and apply the formula for tension in a spherical pressure vessel, using the static head of the fluid concrete. Add a safety factor because the "bubbles" will not all be spherical. I think it is worth a try. Second question is whether the bit will cut the geotextile or try to pull it out when you drill the intermediate piers. You may need to wait a little longer before drilling.

A different approach might be to cast the pier with coarse, lean, zero-slump concrete and no steel, then re-drill it after the concrete sets.

 

[hokie66]

Why is it a problem to lose a bit of concrete into the voids?

aeoliantexan, it is a secant pile wall. There will be no reinforcement in the female piles which are cast first.