Geosynthetics April/May 2021 - 22

Development of a new design method for geosynthetic-reinforced RPEs

FIGURE 6 Scheme of the 1-DOF oscillator

nature of the active force doesn't consider any creep effect and considers a
higher dynamic tensile modulus of the
geosynthetics than the static one.
*	 Repeated impacts produce larger
and larger outward displacements,
which can bring it to the pullout
failure of the wrapping length of the
reinforcement. Hence, this length
shall be designed to be much longer
than in static conditions; connection of the frontface and backface
reinforcement, that is a back-to-back
design, is highly recommended.
In the Rimoldi-Brusa method these
assumptions translate into the following:
*	 The downward vertical component
of the impact load is resisted by the
embankment fill and may have an
effect only on the bearing capacity of
the foundation and the global stability
of the structure and the downhill slope,
while the upward vertical component
of the impact load is resisted by the fill
confined by reinforcement layers.
*	 Hence the soil mass involved in the
impact-extrusion mechanisms is limited by the horizontal planes tangent
at the top and bottom points of the
impacting boulder (Figure 6), and

FIGURE 7 Portion of the RPE involved in a potential impact
22

Geosynthetics | April May 2021

laterally by two planes diverging from
the boulder lateral limits according to
a load-spreading angle, α.
Moreover, the following rational
assumptions are made for the compressed
zone at the upstream face:
*	 Geosynthetic reinforcements cannot work in compression; hence,
reinforcement placed in the direction
of the impact ( " transversal reinforcements " ) may not contribute to penetration resistance.
*	 Only reinforcements placed along the
axis of the embankment ( " longitudinal reinforcements " ), if present, can
contribute to resist the impact load
through the tensioned-membrane
effect generated by the deformation
of the reinforcement like the cord of
an arch. This effect can be considered
as an increase of the load-spreading
angle, α.
*	 The soil resists the impact load through
its coefficient of viscous damping, C,
and its elastic passive resistance with
an overall elastic coefficient, K, which
is given by the sum of the elastic coefficient, Ks, of the soil and of the elastic coefficient, Kg, of the geosynthetic
reinforcements (as said, only by the
longitudinal ones, if present).
*	 The elastic coefficient, Ks, of the soil
is assumed to be proportional to the
Winkler modulus, Mw, of the compacted fill; while the elastic coefficient, Kg, provided by the longitudinal reinforcements is assumed to be
proportional to their ultimate tensile
strength, Tu.
*	 The upstream-facing system contributes to the elastic passive resistance
through a coefficient, Cg, which modifies the overall elastic coefficient, K:
the higher the facing rigidity and the
higher the coefficient, Cg.
*	 The coefficient of viscous damping,
C, is assumed to be proportional to
Geosynthetics April/May 2021

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