Geosynthetics April/May 2021 - 20

Development of a new design method for geosynthetic-reinforced RPEs

FIGURE 5 Reinforcement layers offer
a preferential plane for shear rupture
(Ronco et al. 2009).

The Rimoldi-Brusa
method is derived from
the Italian standard
(UNI 11211-4:2018),
so it is based on the
resistance capacity of
the embankment to
impact, and it allows
the designer to estimate
uphill block penetration
and downhill extrusion
of the geosyntheticreinforced RPE.

20

Geosynthetics | April May 2021

of the proposed method, while the
method will be fully presented in future
conferences and journals.
The Rimoldi-Brusa method is derived
from the Italian standard (UNI 112114:2018), so it is based on the resistance
capacity of the embankment to impact,
and it allows the designer to estimate uphill
block penetration and downhill extrusion
of the geosynthetic-reinforced RPE.
The aim of the authors is to develop
an engineering design method that is
a calculation model based on rational
physical assumptions derived from available research and that can consider the
effect of almost all the variables playing
a role in the resistance to penetration
on the upward face and the resistance to
extrusion on the downward face to finally
compute approximate, yet consistent,
values of the penetration depth and of the
extrusion length.
An engineering design method for RPE
should allow the designer to understand:
*	 How do the geosynthetics perform
under impact?
*	 Do they " stretch " ?
*	 Do they " slide " or " pull out " ?
*	 What is the geosynthetic strain limit
to choose?
*	 What is the impact of load spreading afforded by the inclusion of the
reinforcement, especially if the impact
is not perpendicular as it is on realscale tests (Figure 5)?
*	 What is the reinforcement design
strength to consider?
*	 What is the benefit given by close
reinforcement spacing?
*	 What about the inclusion of a longitudinal reinforcement layer? What is the
effect of different types of upstream
and downstream facing?
*	 What is the effect of thinner or thicker
cross sections?
*	 What is the effect of soils with different compressive resistance and friction angles?

The Rimoldi-Brusa method answers
all these questions; hence, the designer
can quickly try different solutions and
finally select the best combination of
design variables that respect all design
limits and factors of safety.
Reinforcement layers, made of
geogrids or geotextiles, can spread the
impact load along the embankment axes
in both transversal and longitudinal ways.
By using this method, the designer
could also understand the benefit given
by the inclusion of a longitudinal geosynthetic reinforcement. The longitudinal
reinforcement can help in dissipating the
energy in case of non-RPE-perpendicular
block impact and repeated impacts, and
in avoiding punching-type failure in favor
of a larger envelope-type failure.
The Rimoldi-Brusa method is based
on the following assumptions (derived
from Peila et al. 2002):
*	 Being that the impact is an impulsive action in nature, the falling rock
transfers to the embankment the
momentum and the angular momentum of the motion. The impulsive
force that is instantly applied to the
embankment depends on the mass,
the shape and the velocity of the rock,
and on the mass, geometry, geotechnical properties and construction
method of the embankment.
*	 Moreover, the response depends on
the number, position, layout and technical characteristics of the reinforcing
geosynthetics.
*	 The energy wave generated by the
impulsive force applied to the
embankment propagates in a quasispherical shape.
*	 This means that below the rock
imprinting in the front face, the soil
is highly compressed, while above
the imprinting, the soil is subject
to upward vertical stresses, which
would lift the mass of soil above if
reinforcement is not present.
Geosynthetics April/May 2021

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