Slurry Displacement Method

[abusementpark]

I often heard of this method for installation of drilled shafts, but have never anyone explain how it precisely works.

Can anybody give me a quick summary of this??

 

[Drumchaser]

This method is employed when the excavation will not stay open and ground water cannot be controlled by casing due to various reasons, and at various depths (including from the onset) of drilling.

Bentonite is mixed with water (on-site preferably) to a spec. gravity, and viscosity required by the exist. conditions.

Drilling in slurry produces a filter cake on the sidewall of the shaft thus discouraging influx of water, also the hydrostatic head and or downward pressure of a shaft full of slurry stabilizes the walls until such time as concrete can be placed.

This is the short version....placing concrete (w/ tremie) is a whole other topic.

Bentonite I have seen used came from Bariod and is essentially clay dust from the Black Hills of Wyoming...I think.

 

[abusementpark]

So is the bentonite/slurry pumped out before the concete is pumped in??

 

[hokie66]

No, the concrete is placed from the bottom by tremie and displaces the bentonite upward. The bentonite is collected and recycled. So the bentonite stabilizes the walls while drilling and until the concrete is in place.

 

[Zambo]

Polymer drilling fluids are also available. There are various advantages/disadvantages for using polymer, bentonite or a mixture of both.

Tests have been made which show that the placement of concrete by tremie to displace the drilling support fluid does not have a detrimental effect on the bond between rebar and concrete.

In Asia it is not unsual to have bored piles (drilled shafts) constructed by this method in excess of 100m depth.

 

[abusementpark]

Is the bentonite placed in the shaft as it is being drilled?

 

[Zambo]

Yes

 

[Drumchaser]

Zambo

There have been problems with the Polymer slurry. It is no longer allowed in my work areas.

 

[Zambo]

Problems..... There are advantages/disadvantages of polymer and bentonite. The main disadvantage of polymer is the cost which the polymer manufacturers say is compensated for by reuse advantages.

For bentonite the main disadvantage stated is the possible effect of debonding of the concrete to rebar, and the coating of the bore wall which affects the friction capacity of the pile. Both of these properties are enhanced by the use of polymer.

 

[Drumchaser]

As stated....the Polymer slurry is not allowed. This is not to say it is/has been used with great success in many, many other areas ...globally.

Just not here.

 

[Zambo]

Drumchaser, not disputing it's not allowed in your area. Just interested to know whether it is banned on environmental concerns or performance as a drilling support fluid.

 

[Drumchaser]

OK...it is my understanding that the Polymer slurry properties must be more carefully monitored.

I do not have firsthand knowledge of the "settlement" problems associated with this product....only documentation of a moratorium on its use at the present time.

Apparently at several locations shafts were turned down due to obvious problems.

It may have very well been attributed to mismanagement of the operation and or said product.

Not environmental.

Have you used this product routinely with much success?