Belled Pier Capacities
Belled Pier Capacities
(OP)
Received a geotechnical report for a project site that has expansive clay soils. In the report is states that the belled pier capacity is to be reduced when the spacing of the bells is less than 3 bell diameters (clear space) based on the larger pier. The reductions are 40% for 2-3 diameters and 60% for 1-2 diameters.
Given that some of our columns are spaced rather closely together in certain areas we can't get many of the piers to converge on a solution. Does anyone have any literature on reduced capacity of belled piers based on proximity to other piers. I need some background knowledge so that I can convince the geotech to ease up on these reductions.
Given that some of our columns are spaced rather closely together in certain areas we can't get many of the piers to converge on a solution. Does anyone have any literature on reduced capacity of belled piers based on proximity to other piers. I need some background knowledge so that I can convince the geotech to ease up on these reductions.






RE: Belled Pier Capacities
RE: Belled Pier Capacities
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RE: Belled Pier Capacities
"...that the belled pier capacity is to be reduced when the spacing of the bells is less than 3 bell diameters (clear space)."
Spacing of 3 diameters is the commonly accepted spacing to prevent group action. This applies to both driven piling & drilled piers, whether they are point bearing or friction.
The loop hole you can present is that all credible references that I'm aware of measure the 3 diameters from center to center, not clear space - that is a big difference. Check out references such as "Principles of Foundation Engineering", by Braja Das. Also, make sure that you are reading the report correctly.
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RE: Belled Pier Capacities
RE: Belled Pier Capacities
The pile diameter rule usually applies to skin friction piles, so it might be worth a call. The bell interaction should have more to do with the bulb around the bearing region. We put a lot of piles in CH or CM clay.