Pouring Piers with Water in the Hole 1

[cnstengineer]

I'm working on a project where we are installing concrete piers that are drilled approx 24 - 25' below grade. The drilled caisson portion of the pier has a signficant amount of water in the hole. The contractor would like to pour the piers using the tremie method and pump the water from the top of the hole as the concrete is poured, displacing the water from the bottom up. Is it okay to leave the concrete un-vibrated? I'm concerned with vibrating the concrete and mixing the water in with the concrete. Also, how should the top portion of the concrete be handled, as this will most likely be contaminated with the water? Should this be chipped away to get down to sound concrete?

 

[charliealphabravo]

Couldn't the concrete be vibrated immediately after the pour and after the water has been displaced? Also there may be additives that could help. Perhaps the mix design could be discussed with the supplier.

 

[Michel60]

Good morning cnstengineer,

Tremie concrete is placed as a very fluid mix and vibration may not be needed or even advisable. If done properly it is essentially self-consolidating. However there could be some clean-up and trimming of the top of a completed pile that will be necessary. I've had piles and barrettes placed at nearly 200 feet under water/drilling fluid with good results and no vibration. The placing of concrete with a tremie isn't something you want some one learning how to do on your project. If the pipe is withdrawn to quickly or isn't kept charged you can get some pretty awful results. I'd want to see the history and qualifications of the sub performing the work.

regards,
Michel

 

[MiketheEngineer]

Pump the water out??

 

[Michel60]

Pumping the water is preferred if the inflow isn't too rapid and it isn't "falling" into the hole from a seam/perched water. Also pumping the water can lead to instability of the shaft in some cases. So yes, Mike is correct, pump the water first if feasible, otherwise tremie.

regards,
Michel

 

[Eldorado]

I also agree with Mike to pump out the water. It would also be helpful to know where the water is coming in. Is it perched water coming in thru the sides of the shaft excavations? If so, installing a casing to cut the water off is typically done in my area of the country. Concrete is placed thru the casing and the casing retracted, but the bottom end kept below the concrete line.

I also have to echo Michael60's comments on having an experienced contractor handle the tremie, if need be. Having a plastic tremie hose backed up with concrete fall into the bottom of a partially placed pier happens more than you would think.

 

[JAE]

If you can install steel casings to cut off the water adequately then pumping might be an option.

Without casing, as mentioned above, pumping the water might create conditions of soil instability.
The use of the tremie method works well - sometimes you need to use casing to stabilize the side walls

You don't typically need to vibrate the bottom portions of a drilled pier - usually only the top several feet.

Specify that the contractor provide clear, defined troughs for the water to flow out away from the piers. Then require the upper 3 to 6 inches of the pier to be cut off after partial setting to remove any concrete contaminated with too much water.

 

[cnstengineer]

I should have mentioned that these caissons are in an area adjacent to a stream so pumping the excavation prior to pouring is not feasible, even with a casing. Thanks for the responses. Very helpful.

 

[PilebuckEngineer]

Tremie concrete with a shaft type mix will work fine. Pouring into a hole from the bottom up with water in it is what it's made to do. Most state DOT's have a designation with "P" behind it for shaft concrete. Vibration is not needed with the right mix. If you are concerned added CSL tubes or coring at random afterwards will check for voids. I second the opinion that you will have a lot of latents and sludge on top, but that's easy to vac off and chip down to good mud.

 

[TXStructural]

Use a good pump mix. Pump the concrete through a connected (pressurized) tremie (we have seen PVC pipe work in shallow holes, but I'm not recommending it for higher pump pressures.) Keep the tip of the tremie in the fresh concrete, withdrawing as you pump. Continue pumping until all of the water and some good quality, fresh concrete is rolling out of the top of the hole. This is VERY commonly done to place concrete in standing water. I don't have an ACI reference in front of me on a Friday night, but will try to remember to look it up.

 

[Ron]

TXStructural has it right. The ACI reference is "Design and Construction of Drilled Piers", ACI 336.3