Belled Drilled Piers in Sand
Belled Drilled Piers in Sand
(OP)
Is it possible to construct a belled drilled shaft in sand. I am having problems reaching my allowable bearing load and a bell seems to be the only solution. However since i'm in sand I was curious if it was possible. A spread footing seems to be the only other solution, but a quick calc shows an extremely large foundation which will be costly and the client has a preference with drilled shafts.





RE: Belled Drilled Piers in Sand
The geotech had indicated that the sandy clay soils were OK for bells but once the contractor started drilling, the belled out piers caved in. We quickly had to convert to a straight shaft system (yes - 90" diameter shafts) and go from there.
So be careful with bells in sand. Its very difficult to know whether a sandy soil will hold up long enough to allow cage insertion and concrete placement. You may have to use a tremie as well to avoid the falling concrete from hammering the sidewalls of the shaft and initiating collapse of the bell.
RE: Belled Drilled Piers in Sand
As for the tremie I doubt any contractor would attempt to place concrete in bored piles without a tremie.
RE: Belled Drilled Piers in Sand
RE: Belled Drilled Piers in Sand
RE: Belled Drilled Piers in Sand
RE: Belled Drilled Piers in Sand
CE475, I assume this is a stupid question but are you calculating using shaft friction along with end bearing capacity for the bored piles.
RE: Belled Drilled Piers in Sand
RE: Belled Drilled Piers in Sand
RE: Belled Drilled Piers in Sand
Of course everything depends on the soils, but on my latest project (near a river and silt/clay soils) we have 800mm diameter driven precast spun piles which are designed for a working load of 350 tonne with a length of 50m.
RE: Belled Drilled Piers in Sand
RE: Belled Drilled Piers in Sand
RE: Belled Drilled Piers in Sand
Since these structures are often constructed in out-of-the-way places, drilled shafts become more desirable than forming large spread footings. I have seen drilled piers up to 8 to 10 feet in diameter for these kinds of structures and nobody blinked an eye.
I have seen helical piers used frequently in the power industry. For A-Frame type structures, I have designed combined foundations supported by them in the past.
As a side note, AB Chance first developed their helical piers for anchoring guy wires for transmission structures. AB Chance produces a wide variety of power-related products and helical piers are only a small part of that.