2653
Technical Committee 212 /
Comité technique 212
Dembicki et al. presented an analysis of raft foundation
supporting the pylon of cable-stayed bridge in Rędzin.
Important decision on the pile length was their shortening due
to occurrence of confined aquifers which would cause soil
liquefaction under the piles during installation. The decision
could be undertaken after comprehensive numerical analyses as
well as additional investigations of soil parameters. Load tests
with measurement of the distribution of force along the piles
with extensometers were found very useful, allowing the control
of design assumptions. It was concluded that in-situ
measurements with agreeable results from numerical analyses
are the best proof of assumptions made in the design process.
EI – Sakhawy and Nassar investigated the behavior of soil –
pile interaction during soil consolidation by performing several
experimental tests for different conditions such as end bearing
pile and floating tip pile for different soils at the tip of pile.
From the test results authors concluded that;
1. The negative skin friction was developed along the pile shaft
due to consolidation of the soil surrounding the pile under
surcharge loads.
2. The neutral plane was moved closer to the tip of the pile with
increase in the end bearing.
3. The depth of the neutral plane was increased with increase in
the pile length.
Elsherbiny and El Naggar presented a 3D FE analysis using
ABAQUS on helical piles for performance of the pile groups
under axial compressive loads. Mohr-Coulomb plasticity model
is used for soils, where numerical models are calibrated and
verified using: full-scale load testing data of single piles;
representative soil properties obtained from the borehole logs;
and realistic modeling assumptions. It was found that the
performance of a helical pile group in sand or clay is mainly
affected by the pile-to-pile spacing. The practical range of inter-
helix spacing (1D~3D) has negligible effect on the settlement
ratio, R
s
. The factor of safety could significantly affect R
s
for
piles in sand and has negligible effect for piles in clay. In
general, R
s
for helical piles with multiple helices spaced at a
typical pile spacing of 3D is suggested to be 1.15 to 1.2 for both
clay and sand.
Fakharian et al. adopted a numerical approach for studying
the setup effects of a single pile embedded in layered soil strata
by calculating the pile shaft resistance β – parameter. Authors
adopted an axi-symmetric non – linear finite element scheme
for simulating the cavity expansion which occurred due to pile
driving followed by dissipation of pore water pressure and
ageing. Finite element based numerical package ABAQUS was
used for modelling the soil as elasto – perfectly plastic model. It
was observed that an increase in the interface shear strength
between pile – soil was considered to be the ageing component
of the soil setup.
Goto et al. conducted model pile load tests on grouped piles
in large tank of dry sand. 9 cylindrical model piles of 40mm
diameter were tested under 50-200kPa load pressures. Test
results were discussed at yielding point of the total load, tip
stress distribution of the grouped piles, pressure distribution in
the soil measured by the sensors and ground deformation after
the loading tests. The authors suggested that the group pile of
2.5D spacing caused significant interactional effect between
piles and it will behave as a block. In contrast, the piles in a pile
group of 5.0D spacing was reported more independently.
Gusmão et al. presented main aspects of design, execution
and control of shopping centre construction of 280,000 m2 area
in Recife, Brazil. Geotechnical characterization revealed that
soil consisted of silty clays. Static pile load tests were
conducted on 400mm and 500mm diameter piles with allowable
loads of 700 and 1,150 kN. The Van der Veen equation was
used for extrapolating the results of the geotechnical rupture
load for the load tests which may help in the design. It was
found that as the number of sample increased standard deviation
increases and probability density function around the mean
decreases and the curve with flatter appearence can be
observed. With increases in sample space, population dispersion
is incorporated into sample and standard deviation was found to
increase with increase in dispersion, reliability index decreases
probability of failure was found to increase.
Gwizdala and Krasinski discussed the cases of bridge
structures founded on driven displacement piles. It is pointed
out that the general principles given by Eurocode 7 should aim
at an unification of the methods for the calculation of bearing
capacity of the pile. It would be important to create the
international database with complete static and dynamic test
results and the information regarding the soil resistances over
the pile shaft and under the base referred to careful description
of the subsoil and the in situ tests itself.
Haberfield described the design of piled raft for two
buildings (Tall towers and Nakheel tower (1000m high)) in
Dubai which is founded on weak carbonate rocks and a group of
tall towers (up to 300 m high) founded in deep alluvial soil
deposits based on serviceability condition to find out ground
modulus based on various field testing adopted. To get accurate
results pressuremeter, seismic crosshole test and Osterberg load
cell test were used to evaluate the geotechnical properties of
foundation material for two towers. Test result revealed that
significant thickness of debris was found at the base of pile toe
which made the elastic modulus estimation challenging and its
estimation is made on unloading and reloading response of pile
load test.
Hai and Dao performed two bidirectional loading tests on
piles to determine pile capacities for the foundation of 12-story
Sea Bank Building project in Da Nang City, Vietnam. Authors
validated the capacities of pile with pile load test programme of
the bidirectional O-cell test as it is the best suitable for the
limited project. From the test results authors concluded that
maximum upward movements were 3.3 and 7.4mm and
maximum downward movements were 28mm and 49.3mm for
the two tests, the maximum upward movement of pile head
were 0.2 and 2.5 mm respectively and the shaft resistances
above 30 m depth were not full mobilized.
Hamova et al. briefly described the effects of landslide of
width in the top 55m, length 38m and depth 8 to 9m that
occurred on main road and affected more than half of the
roadway. From the analysis authors mentioned that ground
water table raise, river erosion undermining the slope and the
dynamic effects of transport were the main factors for slope
instability. Authors designed and recommended cantilever
retaining wall on driven pile foundation. Authors observed the
proposed structure for period 2006 – 2012 and concluded that
the landslide was successfully stabilized and new landslide
deformations had not been established.
Herrmann et al. investigated the load-bearing behaviors of
bored piles with different enlarged bases. According to DIN EN
1536, overboring of the bottom of drilled piles to increase the
bearing resistance is permissible up to three times the pile
diameter. To validate the supports of design specifications,
model tests at a scale of 1:25 were performed. The tests showed
that an enlargement contributes significantly. By the use of a
reduction coefficient of 0.75 for the bearing resistance, covering
the disturbance effects of the drilling the enlargement, the
bearing resistance would be underestimated. The results were
evaluated against the available results of large 1:1 drilled pile
experiments.
Ishikura et al. discussed the technology of using surface
stabilization and floating type deep mixing soil stabilization for
acceptable settlement where the performance of piles on deep
soft soil layers is maintained. Consolidation settlement
properties and skin friction of model test of grouped piles were
investigated. Two types of model tests and full scale FEM
analysis were conducted. The full mobilization length of skin
friction was found to be increased with elapsed time and it
would converge to the constant value during the consolidation.
Simple forms of the formulations are presented to calculate the
skin friction of floating type column and equivalent conversion
