1. DESIGN AND MODELLING BY DISCRETE ELEMENTS OF
TREE-ANCHORED ROCKFALL PROTECTION FENCES
G. De la Cruz Alcalá* ( UCLM )
I. Olmedo-Manich ( G.T.S. )
F. Bourrier ( IRSTEA )
* Contact: gonzalo_cruz_alcala@hotmail.com
Rockfall is an issue of special importance in mountains areas since they can represent
relevant socio-economic and environmental consequences. This danger has been
increased during the last years with the intensification of the implementation of
infrastructures and facilities in these territories.
This research is developped within the french national projet C2ROP which aims to
involve the whole french rockfall hazard management community (practitioners,
engineering companies, contractors and researchers). It is organized around 3 axes:
Hazard Characterization, Protection Devices Design and Risks Management.
This work isincluded within te second axis of C2ROP. The objective is to design and
model, based on the Discrete Element Method (DEM), a new protection device:
“Tree-anchored Rockfall Protection Fences”. These structures, designed for low-energy
impacts (up to 150kJ), make use of the trees to replace the anchorage metallic piles,
which require of the use of heavy machinery during the construction allowing to reduce
the environmental impact and the costs during the construction.
INTRODUCTION AND CONTEXT
TREE-ANCHORED ROCKFALL PROTECTION FENCES
This innovative system developed by G.T.S
can de composed by one or several
segments. Every segmentis formed by many
modules (up to 4) connected by an upper
and a lower cable. Every module, except
those located on the line ends, contains a
chain link mesh (TUTOR) which is the
intercption component. Every fence is also
attached by lateral cables.
Two types of links to trees are used. A-Class joints are installed at the cable endings to
fix the cables using shackles located at both sides of the trunk in the structure line.
B-Class are used for cable guidind and they are used in the sense of the slope
perpenduclar to A-Class.
The TUTOR net is installed with its longitudinal sense on the horizontal ditection.
Using this disposition, special spires are used to connect the net and vertical cables. On
the contrary, the link to horizontal cables is built zigzagging the cable between the
mesh.
EXPERIMENTAL CAMPAIGN
Tensile tests on the mesh have been
carried out in order to characterize its
mechanical response. Remarkable
differences with the data provided by
the manufacturer are found. This
inaccuracy is associated to the
appearance of stress concentration
points close to the corners.
In addition, full scale impact tests have been carried out. Only a single module has been tested subjecting it to a
controlled impact of a block guided by a zip line. The campaign was performed in N. Damme de Commiers in the
period from the19 May - 31 to the May 2016
To study its structural behaviour, force captors are installed in both horizontal cables and in one of the lateral cables.
A high-speed video camera is used to control the block’s trajectory.
A numerical tool based on DEM has been
built. using spheres (mesh and block) and
grid elements (cables, shackles and trees).
Material properties are mostly obtained
from the literature. However, TUTOR
properties are deduced from tensile tests.
To validate the model, only the 31 of May
test could be employed. Test conditions are
simulated and the numerical and
experimental responses are compared (see
figures on the right). The model provides a
good response when cables loading and
impact duration is studied. On the
contrary, remarkable differences are found
in terms o dispalcements (specially in the
vertical component)
NUMERICAL MODEL ON DEM
In addition, a parametrical analysis is carried out in order to:
1) Identify the influence of
some design parameters
2) Guide and put in
evidence to which
properties a special
attention must be paid to
improve the behaviour of
the model
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