Analysis, design and construction - Practical Engineering Geology - page 248

Reaction dead
weight
(kentledge)

Spreader beam

Displacement
measurement

Jack and load
measurement

Reference
beam

Displacement

Support for
reference
beam away
from test

Most of
load in
skin
friction

Load carried
by skin
friction at
higher level

Skin friction
reduced to
'residual'

1 2 3

End bearing
failure

Load

1 2 3

Residual
settlement on
removal of
load

settlement at
top of pile

'Elastic'
settlement of pile
and ground

Figure 6.10 Typical set-up for pile load test. At early stages (1), most of the ground resistance will
come from skin friction at shallow depths. End bearing is not mobilised until later stages (2) and (3)
of the test (depending on the con le). The rate of settlement

increases as the ground resistance becomes fully mobilised and there will be some permanent
displacement (residual settlement) once the pile is unloaded.

guration of the pile and ground pro

performing until a test approaches failure ( Figure 6.10) . Recently, a
system has been introduced where Osterberg cells are incorporated
into the pile construction at depth and then expanded against the test
pile, both upwards and downwards (Figure 6.11). The end-bearing
resistance below the cell is balanced by the skin friction from the soil
above the cell. This systemwas used for the Incheon Bridge design, using