Cased Piles vs Auger cast piles (ACP) 2

[pelelo]

Hello,

I have been working for a while in the design of auger cast piles. Now I notice some project specifications in my area require piles with casing instead of ACP.

To my knowledge, for axial capacity purposes, I guess the cased depth will not contribute to any skin resistance (or maybe a very low contribution), therefore the pile capacity will be developed by the uncased soil depth (therefore would make the pile longer compared to an ACP). Probably for lateral capacity purposes these cased piles provide higher lateral capacity that ACP. Please correct me if I am wrong.

Bassically I would like to know what are the advantages and disadvaanges of ACP vs cased piles?. No question cased piles are way more expensive as you need to deal with circular steel profiles and maybe the time of construction, compared to a ACP, would be longer.

My point is, using ACP, yet, I don´t see the point of dealing with cased piles.

Please let me know your feedbacks.

Thanks.

 

[JAE]

ACP tend to be smaller and use skin friction (sometimes some end bearing) and you are right that in areas where water inflows are a concern, they are a better choice.

Drilled/cast and (sometimes) cased piers can and are drilled to much larger diamters (I've done a 90" dia. before) and also can be augmented with belled bottoms for total end bearing conditions.

In non-water situations where casing isn't needed, drilled piers are great. If the soil can't support bells, has water, etc. the use of an auger cast pile might be a better choice.

 

[motorbiketocrank]

Would help if you could clarify:

- What do you mean by cased piles? For example do you mean micropiles with a cased upper portion and pressure injection at the base?

- What is the soil strata in these applications?

The pros and cons of various pile types will vary based on the stratigraphy, economics, site layout, etc, etc.

 

[Ron]

There are many reasons to select various type of piles. ACP are typically used in sandy soils where needed capacities are less than 50 tons per pile and the depth of the piles is less than 50 feet. They are used with or without competent end bearing.

As JAE noted, another form of ACP is a wet method drilled shaft or pier. Both are used in areas where water and sloughing soils are issues.

Cased piles or piers have appropriate application as well, though usually they are used in areas where high end bearing is available and there is less need for skin friction as a major component of the pile capacity.

In short, the selection of a pile type has to do with soil stratigraphy, geology, needed capacity, installation limitations, cost, and history of performance in the area.

 

[molerat2210]

Pelelo,

I am not sure if your spec is intended to mean permanent or temporary casing? If may just mean that a temporary casing is to be provided to prevent soil inclusions in the shaft. In this case a ACP or drilled shaft could satisfy the intent of the spec. It is good to keep in mind that specs were written by people and may be less than perfect. Personally, I have never seen a drilled shaft with a permanent casing. That would be very costly.