Geosynthetics April/May 2021 - 24

Development of a new design method for geosynthetic-reinforced RPEs

To the authors'
knowledge, the
Rimoldi-Brusa method
is, at present, the
only design method
for RPEs that takes
into account all
the parameters
contributing to the
penetration and
extrusion resistance.

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24

Geosynthetics | April May 2021

*	 Given the impulsive nature of the
impact load and the consequent
impulsive state of tension in the
extrusion zone, a reduction factor
for impulsive conditions, RF imp, is
applied to the pullout force, which is
calculated with the pullout factor, fpo,
valid in static conditions.
*	 The residual energy, Es, is assumed to
be equal to the work done by the friction and pullout forces, which allows a
calculation of the extrusion length, Lv,
on the valley side of the embankment.
The impact analysis allows the setting
of the required geometry of the embankment, such as the height, H, the crest
width, Lu, the slope angles on the mountain side, βm, and on the valley side, βv;
and the required layout of reinforcement
(type, strength, vertical spacing in transversal and longitudinal directions), by
considering the following design targets:
*	 The maximum allowable penetration
length shall be less than half of the
embankment width at the bounce
height of the impacting boulder, in
order for the impacted embankment
to be repaired with simple maintenance works.
*	 The maximum allowable extrusion
length shall be less than 20% of the
embankment width at the bounce
height of the impacting boulder,
in order to avoid instability of the
whole embankment.
Then such geometr y and reinforcement layout shall be checked for
internal stability with the usual analysis, and for external and global stability considering the accidental load of
the impact force as an equivalent static
force, F imp (kN), applied horizontally
in the center of impact, which can be
calculated as the sum of the equivalent
penetration force, Fp (kN), and of the
equivalent extrusion force, Fv (kN), simply evaluated as energy/movement.

To the authors' knowledge, the RimoldiBrusa method is, at present, the only design
method for RPEs that takes into account all
the parameters contributing to the penetration and extrusion resistance.
Accordingly, rockfall embankments
should be designed by considering
Table 1.
References
Carotti, A., Di Prisco, C., Vecchiotti, M., Recalcati, P., and
Rimoldi, P. (2004). " Modeling of geogrid reinforced
embankments for rockfall protection. " Proc., 3rd European
Geosynthetics Conf., Munich, Germany, 675-680.
Carotti, A., Peila, D., Castiglia, C., and Rimoldi, P. (2000).
" Mathematical modelling of geogrid reinforced
embankments subject to high energy rock impact. "
Proc., 2nd European Geosynthetics Conf. and Exhibition,
Bologna, Italy.
Kar, A. K. (1978). " Projectile penetration into buried
structures. " Jour. of Structural Division, 104(1), 125-139.
Labiouse, V., Descoeudres, F., and Montani, S. (1996).
" Experimental study of rock sheds impacted by rock
blocks. " Structural Engineering Int., 3, 171-175.
Lambert, S., and Kister, B. (2017). " Analysis of existing
rockfall embankments of Switzerland (AERES), Part A. "
Irstea, Saint Martin d'Hères, France.
Mayne, P. W., and Jones, S. J. (1983). " Impact stresses
during dynamic compaction. " Jour. of Geotechnical
Engineering, 109, 1342-1346.
ONR. (2020). ONR 24810: " Technischer
Steinschlagschutz: Begriffe, Einwirkungen, Bemessung
und konstruktive Durchbildung, Überwachung und
Instandhaltung, " ( " Technical rockfall protection: Terms,
effects, dimensioning and structural development,
monitoring and maintenance " ). Österreichisches
Normungsinstitut (Austrian Standards Institute),
Vienna, Austria (in German).
Peila, D., Oggeri, C., Castiglia, C., Recalcati, P., and Rimoldi,
P. (2002). " Testing and modelling geogrid reinforced soil
embankments subject to high energy rock impacts. " Proc.,
7th Int. Conf. on Geosynthetics, Nice, France, 133-136.
Plassiard, J.-P., and Donzé, F.-V. (2009). " Rockfall impact
parameters on embankments: A discrete element method
analysis. " Structural Engineering Int., 19(3), 333-341.
Rimoldi, P., Lorizzo, R., Pettinau, D., Roncallo, C., and
Secci, R. (2008). " Impressive reinforced soil structures
in Italy. " Proc., 1st Pan American Geosynthetics Conf.,
Cancun, Mexico, 789-798.
Ronco, C., Oggeri, C., and Peila, D. (2009). " Design of
reinforced ground embankments used for rockfall
protection. " Natural Hazards and Earth System Sciences,
9, 1189-1199.
UNI 11211-4:2018. (2018). " Opere di difesa dalla caduta
massi-Parte 4: Progetto definitivo ed esecutivo, "
( " Rockfall protection works-Part 4: Definitive and
executive design " ). UNI-Ente Italiano di Normazione,
Milano, Italy (in Italian). G


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Geosynthetics April/May 2021

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