2520
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
FLAC3D3.10
ItascaConsultingGroup, Inc.
Minneapolis,MN USA
©2006 ItascaConsultingGroup, Inc.
Step3676 ModelPerspective
10:49:27MonSep292008
Center:
X:1.126e+001
Y:2.046e+001
Z:9.320e+000
Rotation:
X:110.000
Y:130.000
Z:360.000
Dist:7.957e+001 Mag.: 3.05
Ang.: 22.500
Surface
Magfac= 0.000e+000
ExaggeratedGridDistortion
Livemechzonesshown
Axes
Linestyle
Block State
Livemechzonesshown
None
shear-nshear-p
shear-p
shear-p tension-p
tension-p
History Location
11131617
1001 1003 1006 1007
21232627
31333637
41434647
51535657
61636667
71737677
Figure 2. Plasticity zones during the one stage excavation of the
examined stone column
FLAC3D 3.10
ItascaConsultingGroup, Inc.
Minneapolis,MN USA
©2006 ItascaConsultingGroup, Inc.
Step42971 ModelPerspective
07:52:29FriSep262008
Center:
X:6.840e+000
Y:8.394e+000
Z:5.784e+000
Rotation:
X:120.000
Y:130.000
Z:360.000
Dist:7.957e+001 Mag.: 5.96
Ang.: 22.500
Surface
Magfac= 0.000e+000
ExaggeratedGridDistortion
Livemechzones shown
Axes
Linestyle
Block State
Livemechzones shown
None
shear-nshear-p
shear-nshear-p tension-p
shear-n tension-nshear-p tension-p
shear-p
shear-p tension-p
tension-nshear-p tension-p
History Location
121
123
126
131
133
136
137
141
143
146
147
151
153
156
157
161
163
166
167
171
173
176
177
187
Figure 3. Plasticity zones during multi-stage filling of the stone column
with crushed geomaterial at depth of 16 to 15m simulated by an
equivalent static radial pressure (sub-stage IIIa, 8
th
ascending step of
construction of the examined stone column)
FLAC3D 3.10
ItascaConsultingGroup, Inc.
Minneapolis,MN USA
©2006 ItascaConsultingGroup, Inc.
Step115079 ModelPerspective
20:07:50SatSep272008
Center:
X:1.265e+001
Y:1.964e+001
Z:7.970e+000
Rotation:
X:120.000
Y:120.000
Z:360.000
Dist:7.957e+001 Mag.: 4.77
Ang.: 22.500
Surface
Magfac= 0.000e+000
ExaggeratedGridDistortion
Livemechzones shown
Axes
Linestyle
Block State
Livemechzones shown
None
shear-nshear-p tension-p
shear-p
shear-p tension-p
tension-p
History Location
111316
17
1001
1003
1006
1007
21
23
26
27
31
33
36
37
Figure 4. Plasticity zones during multi-stage filling of the stone column
with crushed geomaterial at depth of 1m to head of the stone column,
simulated by an equivalent static radial pressure (sub-stage IIIa, 23
rd
final ascending step of construction of the examined stone column)
6. CONCLUDING REMARKS
For the needs of the present project it has been decided to adopt
a rather simple, yet representative, soil profile corresponding to
a bridge pier, where typical stone columns of 0.8m diameter and
23m length are constructed, in order to improve foundation soil
behaviour. The complex system consisting of a stone column
and the surrounding soil is numerically analyzed with FLAC3D
numerical code based on finite differences.
The numerical code used considered the procedure of
construction, as well as, its effects on the surrounding soil, and
simulated at its best, the physical procedure of the stone column
construction, in a rational and well documented way.
Excavation stage is simulated in one and unique stage,
whereas, construction of a stone column is simulated by a multi-
stage complex procedure divided in two distinct calculating
steps. Those are identified as two sub-stages per ascending step
of construction: a) vibration and compaction, materialized by
application of an equivalent radial pressure against the internal
wall of the cylindrical excavation and b) stone column filling
with a linear elastic geomaterial assigned a high elastic modulus
of compressibility, due to the compaction procedure, preventing
a rebound of the induced radial displacements of the first sub-
stage.
Commenting the outcome of numerical analyses performed,
the following points can be outlined:
1. after completion of excavation stage, the plastic zones
developed around the cylidrical excavation are limited,
same as horizontal displacements, ranging from some
millimeters to only a few centimeters,
2. once excavation procedure is completed, it has been
documented via a “trial and error” back calculating
procedure, that a zone of about 60cm is seriously disturbed,
affecting notably the mechanical and deformational
parameters of the surrounding soil,
3. the stage of constuction of the stone column has been
simulated by a multi-stage procedure of ascending steps of
1m and application of an equivalent static radial pressure,
as defined in §4.2, progressively reduced as ascending
construction steps approached the head of the stone column
at the free surface,
4. horizontal inelastic displacements in the limit of the side
wall of the cylidrical excavation range between 10 and
20cm, resulting thus in an expansion of the constructed
diameter, compared to the theoretical one as designed.
7. REFERENCES
Edafomichaniki s.a. 2007. Egnatia Odos s.a., section of Nestos bridge
and road access on it (14.1.2/14.2.1). Geotechnical Final Design
Study (boreholes GT1 to GT5).
Itasca Consulting Group Inc. FLAC3D v3.10 : Fast Lagrangian
Analysis of Continua. User’s Manual version 3.10.
Itsak and Gazetas G. 2003. Study of seismic response and evaluation of
liquefaction risk.
Issue 1,
pp 73.
Mylonakis G., Nikolaou S. and Gazetas G. 2006. Footings under
seismic loading: Analysis and design issues with emphasis on
bridge foundations.
Soil Dyn. Earthquake Eng., 26(9), 824-853.
