2583
Technical Committee 211 /
Comité technique 211
The algorithm for calculating the proposed technique is
based on the tensile force dependence in the geosynthetics
F
a
on
the size and shape of the collapse, the reinforcing interlayer
depth, the surface load and geosynthetic material elongation .
Our studies showed that the tensile force – elongation
dependence is determined most accurately with the use of the
formula similar to that in the BS 8006 standard
a
Dq h k
аF
6
1
1
)
(
5,0
,
(1)
where
k
is the coefficient taking into account the supposed form
of the collapse (for the rectangular collapse – plane problem – it
is equal to 1). In the British standard BS 8006 the value of 0.67
for the axisymmetric case is given , but studies showed that
higher convergence with the experimental results was obtained
when
k
= 0.78;
a
is the specific elongation of the geosynthetic
material depending on the tensile force in the reinforcing
interlayer, which is determined according to the graphs (for
example, as shown in Fig. 2);
h
is the depth of the reinforcing
layer, m;
is the specific weight of the ground, which is located
above the reinforcing interlayer, kN/m
3
. If there are ground
layers having different specific weight values and located above
the reinforcing interlayer, it is necessary to make the following
replacement in the formula
n
i
i
i
h
h
1
(2)
where
n
is the number of ground layers above the reinforcing
interlayer,
i
is the specific weight of the
i
-th ground layer,
h
i
is
the height of the
i
-th ground layer;
q
is the equivalent surface
load on the reinforcing layer, кН/м. Its calculation depends on
the surface load amount by analogy with the calculation of the
additional pressure (tension) in the ground mass, as well as on
the load type, the load area-to-collapse region ratio, the surface
load location with respect to the ground collapse;
D
is the
collapse length (diameter), m.
The main problem when calculating by this method is that at
the initial calculation stage we are aware of neither the tensile
force
F
a
, nor the specific elongation of the geosynthetic material
a
because the actual dependence of the elongation on the
tensile load is not taken into account in the formula (1). That’s
why, we used the successive approximations method accurate to
5 %. The received value
a
is used to determine the maximum
deflection
s
a
of the reinforcing material
2
8/3
D
s
a
a
.
(3)
To calculate the maximum ground surface settlement, the
following formula is used,
a
s
h
D s
2
tanθ 2
,
(4)
where
is the inclination angle of the slip plane to the vertical.
The values
depend on the characteristics of the backfill soil.
Since it is necessary to determine the maximum surface
settlement by the current Russian regulations, in practical
calculations
=
is taken. In case the ground layers located
above the reinforcing interlayer have different
values, the
following value is used.
n
i
i
n
i
i
i
h
h
1
1
(5)
The obtained value of the surface settlement
s
is compared
with the normative or design values for this construction
project. If the condition
s
≤
s
и
is not satisfied, then a
geosynthetic material with different characteristics is selected
and the calculation is done again.
To evaluate the proposed method, its comparison with the
results of the experiments and calculations performed by other
methods (BS8006, Giroud, Perrier, R.A.F.A.E.L.) as well as
PLAXIS and Sofistik programs was carried out. Due to the fact
that we were not able to do model experiments in Russia, the
data for comparison were taken from Schwerdt’s works.
Table 1. Results of calculations
Calculation method
Tensile force
in
geosynthetic
material ,
kN/m
Deflection
of
geosynthetic
material,
mm
Surface
settlement,
mm
Experiment
105
90
30
BS8006
64
240
30*
Giroud
215.5
90*
30*
Perrier
120
90
90
R.A.F.A.E.L.
95.8
120
–**
PLAXIS
103
160
–
Sofistik
113
130
–***
Proposed method
114.5
107
34
*-These are initial data according to the indicated methods.
**-Negative values are received.
***-The Sofistik program does not allow to determine the surface
settlement.
4 REFERENCES
Blivet et. al. 2002. Design method for geosynthetics as reinforcement
for embankment subjected to localized subsidence. Delmas; Gourc;
Girard (ed):
Geosynthetics
7. ICG.
Swets & Zeitlinger.
BS 8006: 1995.
Code of Practice for Strengthened/Reinforced soil and
Other Fill, British Standart Institution.
Section 8. Design of
embankment with reinforced soil foundation on poor ground, 98–
121.
Giroud J.P., Bonaparte R.; Beech J.F. 1990. Design of Soil Layer-
Geosynthetic Systems overlying Voids.
Geotextiles und
Geomembranes
. 9Jg, H. 1., 11-50.
Schwerdt, S. 2003. Die Ueberbrueckung von Erdeinbruechen unter
Verwendung von einlagig verlegten Geogittern - Vergleich
zwischen Versuchsergebnissen und den Ergebnissen von
analytischen und numerischen Berechnungen.
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, 26, 95-
105.
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collapse into underground voids.
EuroGeo 3: Geosyntetics
conference
, Munich, Germany, 483-488.
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Tome 1, 93-99.
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Proc.
7.
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und
Vortragstaguung Kunststoffe in der Geotechnik
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Section
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