ae303 intro to deep foundations

8/18/2019 AE303 Intro to Deep Foundations

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• When the soil directly below a building is not strongenough, or the footing size would be larger than practical,

a deep foundation can be used.• Deep foundations can be divided into two types.. A drilled

and poured in place “pier”, or a driven “pile”.

Piers and piles have two components to their load capacity:

End bearing and shaft friction.

Piles are made of:

Steel; H- piles, Steel pipe

Concrete; Site cast or Precast

Wood;.. Often used as temporarypiling today...but wood was used forpermanent piling in the past. Theseare 100+ year old piles under city hall.Wood piles will last “forever” as longas they stay wet.

Driven Piles:8” to 10” pipe piles driven 25’ to 35’ are very common In this area.

H piles are used for soil retaining systemsand to support buildings where the required

pile strength and depth is greater than can becarried by pipe. H piles under the US bank

building in Milwaukee go150’ deep.


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Drilled Piers

Deep FoundationsBell Creator

Shaft Casing

Drilled Piers

Deep Foundations

Rebar Cage Insertion

Rebar Cage

Shaft Casing


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Piles and Piers are always Load Tested

Sometimes the pile is loaded by

pressing against a static deadload.

Piles and Piers are always Load Tested

Sometimes they aretested by reacting

against other piles.


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Deep Foundation Design



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Pile caps are footings used to tie a group of piers orpiles together to support and transmit column loads

to them.

Pile caps: ACI Rules :


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Group Efficiency.

Stresses coming from the piers or piles in the soil mass overlapwhen they are placed too close to each other. The load-bearing

capacity of the group is less than the sum of the individual

capacities .

There are a number

of methods forpredicting the

capacity of groups.

Deep Foundation DesignGroup Efficiency, here are three representative methods of calculation.

1) The Converse-LaBarré method. In this method, η represents the group’sefficiency expressed as a percentage of the theoretical total group load. The

theoretical group load is the ultimate load of each pile multiplied by the total

number of piles.

The ni represents the number of rows and columns, d is the pile diameter and s isthe spacing between piles (center-to-center).

2) The Feld rule reduces the calculated load capacity of each pile in a group by

0.0625 for each adjacent pile. The pile spacing s is not taken into account.

3) The Contractor’s rule reduces the calculated load capacity of each pile by a

factor I for each adjacent pile, where,

ae303 intro to deep foundations

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