2742
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
final load phase was 400 kN approximately which is
equivalent to 11% of total load
Q
max
= 3560 kN;
essential portion of pile settlement (75% approximately) at
the level of pile head (5.5 mm) is related to the shortening
of the pile (4 mm approximately);
settlement of the pile base in the final loading stage reached
the value nearly 2 mm which explains small value of
mobilized soil resistance under the base;
values of mobilised unit friction resistances over the pile
shaft
t
s
in sandy layers varied from 85 to 130 kPa whereas
in mud layers from 25 to 35 kPa. Friction resistances in
sandy layers directly under the soil surface (
t
s1
) reached full
mobilization state corresponding to maximum value
100 kPa. In turn, the friction resistances of deeper sandy
layers (
t
s
2
,
t
s
3
,
t
s
5
i
t
s
7
) did not reach maximum values due to
small pile displacements against the soil occurring at the
corresponding levels;
mobilized unit resistance of the soil under the pile base
q
b
reached the value of 1300 kPa approximately and due to
small displacements of the base is far from ultimate value.
After extrapolation of the curve for the displacements
corresponding to 10% of the pile diameter (50 mm),
approximate value of limit unit resistance of soil under the
base was about 4500 kPa.
Extensometric measurements performed during the load test
revealed that upper subsoil layers took over large portion of the
pile force which made difficult the reliable assessment of the
bearing capacity of basic soil layers lying below. Thus the load
applied in the load test should be much higher corresponding to
Q
max
of the order of 6000–7000 kN. However, due to capacity
of loading stand it was not possible to apply such high loads.
The described case may be a good example showing that the
planning and interpretation of conventional loading tests
requires always individual approach and analysis referred to the
specifics of soil conditions, especially when we deal with
layered subsoil. In such cases it is recommended to carry out the
load tests accompanied by exetensometric measurements.
3 SUMMARY
Driven displacement piles of Vibro, Vibrex and Franki type
have favorable load-settlement characteristics and reveal small
settlements. General principles given by Eurocode 7 should aim
at an unification of the methods for the calculation of bearing
capacity of the pile. Current comparison of the calculation
results obtained by various methods indicated significant
differences in the assessment of the bearing capacity of the
piles.
Experiences and comparative analyses with the results of
load tests show that the most reliable results are obtained in
terms of calculation methods which make use of in situ test
results (CPT, CPTU, DLT, PMT). It would be of significant
value to create the international database with complete static
and dynamic test results of piles and the information regarding
the measurements of soil resistances over the pile shaft and
under the base referred to careful description of the subsoil and
the in situ tests itself.
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