Soil foundations - Geotechnical Investigation and Design Tables - page 278

Table 21.21 Uplift design.

Depth Load Comment

Surface to depth of No shaft capacity resistance Uplift Use1/3 of active zone

desiccation cracking
Surface to depth of

Swelling pressures (U s ) from swelling Uplift Typically 1.5 m to 5.0 m

active zone pressure tests. Apply U s to slab on depending on climate

ground 0.15 U s to shaft and soil +

use C u if no swell test

Below active zone 75% Downward shaft Resistance Due to cyclic softening

resistance dead load +

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Air space may be used below the main beam (a suspended floor system) or a void
former below the slab may be used to resist slab uplift.

21.22 Plugging of steel piles
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The pile shaft capacity is determined from the perimeter, and its length.

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The pile base capacity is determined from the cross sectional area.

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The pile must be assessed if in plugged or unplugged mode, as this determines the
applied area for adhesion and end bearing.

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For H - Pile sections, the soil is plugged if sufficient embedment occurs. The outer
“plugged'' perimeter and area is used.

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For open - ended steel pile sections, a soil plug occurs if sufficient embedment and
the full plugged cross sectional area is used.

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The plugging should be estimated from the type of soil and its internal friction.
The plug forms when the internal side resistance exceeds the end bearing resistance
of the pile cross - sectional area.

•

The table below is a first estimation guide only and subject to final design
calculations as pile pugging can be highly variable.

•

Internal soil plugging for very soft clay showed the internal soil plug moved down
with the plug and achieved a final length of 70% of the length of pile for 400mm
diameter pile.

•

For dense sand 40 to 50% of driven length likely.

Table 21.22 Initial estimate guidance pile plugs based on diameter of open pile.

Strength of material Likely pile plug Comment

Very soft clay 25 to 35 Pile diameters 10 m to 14 m plug formed for a 400 mm

diameter tubular pile (Trenter and
Burt, 1981). Under weight of hammer

Soft to stiff clays 10 to 20 Pile diameters Paikowsky and Whitman (1990)

Very stiff to hard clays 15 pile diameters Assumed <

Very loose to loose sands

>

30 pile diameters Assumed

Medium dense to dense sands 20 to 35 Pile diameters Paikowsky and Whitman (1990)

Very dense sands 20 pile diameters Assumed

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