Proposal of Axel Ruiken of
Geogrid-Soil Interaction Mechanisms
from Plane Strain Model Testing
The
aim of this research project is the investigation of geogrid‐soil
interaction mechanisms in order to describe the behaviour
of geogrid reinforced soil structures. An economic design, however, implies an
exact knowledge of the stresses acting within the reinforcement. The current
research project is therefore taking the benefits from plane strain testing of
geogrid reinforced soil in order to determine the stresses acting in the geogrids.
For this purpose a biaxial compression test apparatus is currently being
developed with respect to the experience gained from first tests with the box
shown in Figure 1. The test box measures (H-W-D) 1m x 1m x 0.45m and has
transparent sidewalls. The geogrids can be placed in the box either without any
connection to the facing or with one side fixed. The clamps for the fixture are
connected to load cells to be able to record the connection loads of the
geogrids at the facing. At testing with fixed geogrids the facing can be
retracted until it is held completely by the geogrids, i.e. state of
equilibrium.
Fig. 1.
Plane strain test box for geogrid reinforced soil
Fig. 2.
Movement of soil particles from PIV analysis
(Soil reinforced with 2 geogrid layers)
Performance
of tests includes homogeneous loading of the geogrid reinforced soil with a
compressed air cushion with up to 50 kPa, followed by
a controlled horizontal displacement (retraction) of either one facing or both
facings simultaneously. The test series include the variation of the number of
reinforcement layers (resp. reinforcement spacing), the type of geogrids (resp.
geogrid stiffness), the stress level, the type of filling soil and the fixture
of the geogrids in order to answer the following questions:
Measurement
of forces and pressures is made with standard load cells at the abutments and
with high resolution foil sensors (approx. 1 measured value per cm²) between
the soil and the facing. Furthermore, redundancy is ensured by measuring the
earth pressure also with 20 load cells, each 5 cm high, forming one of the
facings. Geogrid strains are being recorded with strain gauges attached to the
geogrids. Using the particle image velocimetry (PIV)
method to evaluate photographs taken during testing allows to identify shear
surfaces (Fig. 2) and areas of interlock.