2117
Technical Committee 207 /
Comité technique 207
The BS 8006 concept results in having the highest
connection stress requirements at the footing of the
construction, while research and lessons learned from failures
indicate to have the highest stress levels at approx. 1/3 height
starting from the bottom of the walls.
Nevertheless, the reduction of the lateral earth pressure of
both concepts has a direct influence on the design of reinforced
walls and allows for steep walls with a friction connection
between e.g. blocks and reinforcement.
5 LARGE-SCALE TEST IN SITU
5.1
Design and set-up
In addition to the large scale tests on full height panel walls
performed by Pachomow, a full scale trail has been performed
by KWS Utrecht, Netherlands, supported by NAUE, Germany.
While under laboratory conditions high loads up to 450 kPa
could have been applied to the structure, in situ the influence on
installation procedure, weathering (changes of moisture-content
and temperature) and long term effects caused by the
thermoplastic characteristics of the used high strength Polyester
geogrid could be investigated. Figure 4 gives the cross section
of the test set-up for the in-situ test with geometry comparable
to the laboratory test.
Figure 4. Test setup full height panel wall, KWS Utrecht
To reduce the required amount of structural steel for the
construction, the panel has not been designed using
conventional design methods, but taking the results from
laboratory test explained in Chapter 4 into consideration.
Therefore, the design configuration has been optimized,
assuming the load distribution given in EBGEO, applying an
overall safety to the earth pressure distribution of 1.5
(assumption).
The load distribution has been applied to the panel design,
testing several static systems and designs to optimize the
amount of required structural steel. At the end, the system could
be optimized for transport steel only.
To make the system as easy as possible, only 1.5 m long
strips of the reinforcement have been precast to the concrete
(Figures 4, 5a). The required length of the reinforcement to fit
the overall safety according to EBGEO has been placed on site,
just overlapped by friction. For the earth pressure distribution,
satisfactory pull-out resistance of the strips from the reinforced
backfill has to be ensured.
Several types of instrumentation have been used, taking the
static principle of ΣH = 0 into consideration. The sum of forces
acting on the backside of the panel shall be equal to the forces
acting on the geogrids, the temporary prop, added by the friction
on the toe of the panel.
Therefore, the toe of the panel has been designed as plain
bearing, using geosynthetic components for sliding purposes
with tested and well-known friction parameters for back-
analysis of the forces acting at the toe. Temporary wooden
wedges, applied during placing the panel, have been removed
after the installation of the first 1.5 m of backfill material, so
lateral movement of the panel toe was possible but has not been
observed.
Further on, it had to be ensured that the material used is
applicable to the use in concrete, as it is given here by
independent testing and applying a partial reduction factor for
environmental influences to the polyester material of 1.18 [-].
To predict stress, strain and lateral movement of the stage
construction, finite element (FE) analysis have been worked out
using PLAXIS 2D, 2011. These calculations are also usable for
comparing the measurements and predictions for the reference
times t
0
…t
5
charged as indicator for significant changes in the
static system with construction stage and time, Figure 5.
Figure 5a. Installation procedure and expected deformations of wall.
Secugrid
®
120/40 R6
precast in panel
Secugrid 80/20 R6
placed on site
0.5 m
0.5 m
1.0 m
1.0 m
0.5 m
1.0 m
Horizontal strain of geogrids
Vertical strain of concrete
Axial strain
lateral movement
1.5 m
geogrids connected
by friction
geotextile/
geomembrane
(smooth-smooth)/
geotextile
t
0
t
1
t
2
t
4
t
5
removement
of props
removement
of footing‐support
(long term
stiffness
of geogrids)
(end of
consolidation)
Figure 5b. Time schedule of construction.
5.2
Measuring strain and back-calculation of stress
For the back-analysis of horizontal forces from strain
recordings, the corresponding stress has to be known. This can
be read from isochronous stress-strain curves, as far as they are
available. For the used material here, Secugrid
®
made from
polyethylenterephthalat (PET), the curves are given. The back-
analysis for representative times t
0
, t
1
and t
2
(see Figure 7) has
been worked out using the isochronous curve for 1 hour, repre-
sentative for the situation immediately after compaction of soil.
As this gives conservative values of stress, no further differ-
entiation is required.
For the time t
4
and t
5
, long term stiffness has been calculated
using the isochronous curve for 1000 h, also giving
