2116
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
active earth pressure coefficient, being expected in the range of
0.2 and 0.35, depending on the theory and boundary conditions.
Figure 1 indicates that the normalised lateral stress on the facing
is significantly less for reinforced structures. Furthermore, the
data indicate that the absolute height might not have a decisive
influence at all, but the normalised one.
Ruiken et al. (2010) have demonstrated the arching effects
close to the facing of a geogrid-reinforced soil sample, using
biaxial tests at plane strain conditions. The degree of arching
and the absolute value of stress reduction depends on the lateral
movement of the facing as well as on the degree of
reinforcement, see also Bussert (2006).
Based on full scale tests using several commonly known
reinforcing products varying in a small range of nominal
strength from 40 kN/m up to 55 kN/m a clear tendency can be
obtained concerning the stiffness, described by the secant
modulus J of the products:
J [kN/m] = strength F [kN/m] /strain
[%] (eq. 1)
Figure 1. Compiled data of lateral stress to facing, presented at
normalized height and relationship between normal load σ
h
and lateral
pressure σ
v
.
Figure 2. Deformation of full scale walls with semi-flexible facing,
depending on the product (Pachomow & Herold, 2009).
Figure 2 shows preliminary results of a 4.0 m high
construction using a weak facing system and a load beam 1.0 m
behind the wall surface, applying a top load of up to 350 kPa.
The deformation varies significantly depending on the type of
product. All products performed satisfactory in an acceptable
range, while some products allow for higher loads and show an
enhanced performance in terms of serviceability.
4 EUROPEAN DESIGN CODES
Exemplarily the mostly used design codes in Europe, BS 8006
and EBGEO 2010, dealing with reinforced earth will be
discussed in the following.
Following the basic principles of designing reinforced soil,
based on the results shown in Chapter 3, EBGEO allows further
for a reduction of the lateral stress as compared to the Rankine´s
active earth pressure. The well-known coefficient for the lateral
active earth pressure k
ak
is just used as basic parameter (eq. 2),
taking the inclination of the wall as well as the soil parameters
(e.g. angle of internal friction
´) into consideration. The
correction factor
G
as per Figure 3 is then applied, knowing
well that using the lateral active earth pressure k
ak
as basic
parameter is just an interim solution up to full understanding
and modeling of reinforced earth. In the upper part of the
construction respectively on the actual construction level, the
earth pressure due to compaction (not shown in Figure 3,
typically up to 25 kPa) becomes decisive, but is going to be
superimposed by the earth pressure resulting from the self-
weight of the construction.
E
Facing
= (
g
* ka
gh,k
*
k
* H
i
*
G
(eq. 2)
+
q
* k
aqh,k
*q *
Q
) * l
v
with
E
Facing
Earth pressure on facing [kN/m]
g
,
q
Matching coefficient [-]
k
agh,k
, k
aqh,k
Coefficient active earth pressure [-]
k
Weight of the soil [kN/m³]
H
i
Covering [m]
q
Traffic load [kN/m²]
G
,
Q
Partial safety factor DIN 1054 [-]
l
v
Vertical space between layers [m]
0,00
0,10
0,20
0,30
0,40
0,50
0,60
0,70
0,80
0,90
1,00
0,00
0,10
0,20
0,30
0,40
0,50
h
v
normalised height (H/H
max
) [-]
1.0
0.5
1.0
flexible
1.0
0.7
1.0
semi
flexible
1.0
1.0
1.0
rigid
0.4 H
< h
H
0
< h
0.4 H
q
g
Correction Factor
H
e
ah
h
GTX PEC 55 F (PET)
GG GX 55/30 F (PET)
GG 50/50-30M (PVA)
GG 55/30-20 (PET)
GG 40/40 Q6 (PES)
deformation of facing [mm]
height of wall [m]
top load: 350 kN/m
Figure 3. Correction factors applied to k
ah
according to EBGEO, 2010.
In opposition to EBGEO, the earth pressure following
BS 8006 is calculated using the active earth pressure coefficient
k
ah
for the structure, superimposed by k
0
in the upper part. The
reduced stress acting on the front of the construction depending
on the stiffness of the wall-facings is considered by a reduction
of the connection stress, e.g. by 25 % in the upper 60 % of wall
height using wrap-around method.
