Skin Friction Pile
Skin Friction Pile
(OP)
hi all i need some clarification about skin friction bored piles. what is the normal construction practice? how we can do the Pile testing? i don't have experience in this skin friction pile.
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RE: Skin Friction Pile
RE: Skin Friction Pile
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RE: Skin Friction Pile
Often there will be a casing (section of pipe) which is placed in the ground for the top few metres (maybe 5m. Then the soil is excavated from within the casing and continuing down to the required level. The exvacation can be carried out by various machines including an auger drill or a bucket.
Depending on the soil conditions something will be needed to support the sides of the excavation as you go down. This could be a full depth casing, or water mixed with the soil, bentonite or polymer drilling fluid.
Once you get to full depth then assuming bentonite has been used you will have a circular hole of the correct diameter filled with bentonite. Now you have to lower a rebar cage into the bentonite. Finally you use a tremie tube to place the concrete into the bottom of the excavation and progressively displace the bentonite.
RE: Skin Friction Pile
RE: Skin Friction Pile
RE: Skin Friction Pile
I have always worked on bored piles using either full length casing (London), or bentonite (Malaysia, Vietnam, Thailand, Philippines) or polymer (Thailand) as excavation support. I have also seen trials of a reverse circulation technique where the existing soil (clay in this case) is mixed with water to provide support.
I've never seen bored piles without excavation support, but I suppose it depends on location, dimensions and soil types.
RE: Skin Friction Pile
RE: Skin Friction Pile
When you come across the WT, that means you've got an aquifer with possibly loose sandy or gravelly soil, that stands for 'cave-ins', so whatever support si required is used (regular slurry being the cheapest, casing being the most espensive)
Slurry may be tricky in salty water.
Another tricky situation: a pressured aquifer.
You've got a dry hole in clayey soil, self supporting, no probs whatsoever, no slurry nor casing used, until you drill a little distance above the pressured aquifer, the clay plug resistance is overcome, water almost erupts into the hole, turbulence causes caveins of the water bearing layer and the job which you believed a shoe-in is ruined.
A geologist knowing the area is always a valuable asset in these cases.
RE: Skin Friction Pile
RE: Skin Friction Pile
RE: Skin Friction Pile
RE: Skin Friction Pile
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You will have to get a good quality contractor and insist on a good QA regime.
The first step is the test pile. You may select a test pile with instrumentation so that you can check the perfomance of the pile at different soil levels during the load test.
http://www.pile.com.my/bored.htm
RE: Skin Friction Pile
RE: Skin Friction Pile
RE: Skin Friction Pile
I think bored piles of the diameter and length you require have often been constructed in Sri Lanka. As a personal preference I would choose a contractor with Bauer rigs. Bauer rigs are dependable and well tested with piles of this type.
The first thing is to make sure your SI is reliable. The depth of the SI boreholes should be greater than the required pile length. I have seen cases where the boreholes are at a lesser depth than the pile and it is assumed the SPT's will remain the same or get greater - this is not always the case.
Next you need to decide about the pile test requirements. Test piles are expensive especially with instrumentation. If you only have 6 piles then probably just a load test is sufficient. But if you have many piles then instrumentation will allow for value engineering.
For QA you have to decide whther sonic logging is required or not. This is a significant expense but is getting more common.
You should discuss with proposed contractors whether they propose bentonite or polymer excavation support/drilling fluid. I think in Sri Lanka bentonite will be preferred. A suitable procedure and QA system must be provided.
RE: Skin Friction Pile