2110
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
and deformation modulus
E
def
= 30 up to 112 MPa according to
geological investigation by dynamic penetration testing up to
the depth 40m. Locally in layers with fine-grained gravel with
minimal sand filling the value if
I
D
was 0.15 and deformation
modulus
E
def
= 16 MPa. Average thickness of the quaternary
gravels was 13 m. Neogene sediments were represented mostly
by sandy clays (
saCl
) with firm filling of clay, with sand
locations with addition of fine-grained soil (less than 15 %), to a
small extent also with silts of middle plasticity to clays of high
plasticity in depths of 19.8 to 20.6 m and 25.3 to 26.4 m. The
value
E
def
determined by dynamic penetration tests was 20 to 28
MPa in Neogene soils.
5
CONCLUSIONS
Contact stress in base foundation of the high building was
500 to 800 kPa. Limit settlement determined the type of
foundation (rafts or piles). Based on the information about
disproportionately high compressibility of the subsoil, ground
treatment by deep vibratory compaction was performed. Base
foundation was located in the depth of 4.0 m under the surface.
The raft is 1.4 m thick, in deepened parts 2.0 m. Density of
compaction points was in raster of 2.2 x 2.4 m for stress of 800
kPa, under pad footings and strip footings in raster 2.5x 2.5 m to
1.75 x 3.5 m for stress of 500 kPa and under pads and strips in
raster 1.8 x 1.8 m for stress of 800 kPa. The length of the piles
for stress of 800 kPa was in depth of 3.0 m from the working
base under the surface 10,0 m (i.e. till the Neogene in the depth
of 13.0 m), shortened to 7 m in area with load of 500 kPa.
The key value in the design of high building foundation in deep
excavation pits is the limit usability state. Most questions are
raised by the simulation of soil deformation characteristics and
expected groundwater inflows. Good prognosis of deformations
is based on combination of determining correct soil deformation
characteristics verified by laboratory and field tests in the whole
deformation zone and selecting the right calculation method.
The project must respond to the architect's requirements by
suitable design, its monitoring and potential modification of
stiffness of the retaining structure, subsoil and additional sealing
elements.
Geotechnical design and execution of deep excavations of
high-rise buildings in urban areas are presented in the paper.
Design of the retaining structure and subsoil behaviour based on
the results of in situ measurement during execution with the aim
of minimising the settlement of high-rise building are discussed.
The paper summarizes stability and dewatering problems
associated with design and execution of deep excavations in the
city of Bratislava. The results of geotechnical calculations have
been compared to the results of in-situ measurements.
6
ACKNOWLEDGEMENTS
This arrangement was based on previous comparable
experience in Quaternary gravel sediments of Bratislava where
the verified deformation modulus of the vibrated gravel
columns reached the average value of
E
def
equal to 500 MPa and
increasing of the deformation modulus of average environment
was proved by the values
E
def
from 250 to 300 MPa. The
calculation of the average deformation modulus of improved
subsoil in the area A in question is according to the relation
The present work has been supported by the project of the
Slovak Science Agency VEGA No. 1/0241/13 and by the
Ministry of Education, Science, Research and Sport of the
Slovak Republic within the bounds of OPVaV project No.
26220220140.
7
REFERENCES
Bednárová, E. Minárik, M. Grambličková, D. Sabo, J. 2010. Flood
Protection of Bratislava and its Specifics from the Viewpoint of
Geological Composition of Surrounding Environment. In:
XIV
th
Danube-European Conference on Geotechnical Engineering
:
Proceedings. Slovak University of Technology in Bratislava,
Slovakia, 7 p.
A
EA+EA
= E
s s
g g
def
(6)
where
A
g
is the area of vibrated stone columns
E
g
– deformation modulus of the vibrated stone columns
A
s
– area of the unimproved soil
Kopecký M. Černý M. 2008. Landslides remediation of railway cut in
Bratislava. Czech Journal
Silnice a železnice
. 3/2008. Part
Foundation
E
s
– deformation modulus of the unimproved soil
After constructing the vibrated stone columns, dynamic
penetration tests were performed, located in the middle of the
vibrated stone columns. Increase in the deformation modulus
with depth was also proved, which was taken into account in the
calculation of predicted settlement based on the monitored data.
Average value of
E
def
= 284 MPa was measured under the base
foundation up to depth of 2 m. The predicted final settlements
are summarized in the table 1.
Ťavoda O. and Šabo A.
Foundation below groundwater
. ALFA,
Bratislava, 1986, 272 pp.
Turček P. and Hulla, J.
Foundation engineering
. JAGA, Bratislava,
2004, 360 pp.
Turček, P. and Súľovská M. Using the observation method for
foundation of high-rise buildings. In: Proceedings of the 14
th
European Conference on Soil Mechanics and Geotechnical
Engineering. Vol. 2. Madrid, 2007, Millpress Rotterdam. p. 419 –
422.
Table 1. The values of settlement calculated for different foundations.
Foundation
Settlement
s
(mm
)
Spread foundation without soil improvement
104.46
Spread foundation with soil treatment by stone
columns (
E
def
based on comparable experience)
67.01
Spread foundation with soil treatment by stone
columns (
E
def
based on site testing)
64.55
Pile foundation
73.97
During the construction of the high building the vertical and
horizontal deformations were monitored. The measured value of
settlement after consolidation process reached 52.2 mm.
