Geosynthetics April/May 2021 - 25

TABLE 1 Design considerations for rockfall embankments

Design block
energy and
bounce height

Foundation
bearing
capacity

Boulder mass (size, shape, frequency,
trajectory, velocity, etc.). The kinetic energy
of the impact is determined considering the
velocity and mass of the falling block, and
mathematical and statistical simulations
of material characteristics of the rock and
slope by using specific software, e.g., Rocfall
Rocscience, or other similar tools.
Foundation bearing capacity based on
vertical load from the embankment over
the width of the footprint. The bearing
capacity should be checked against soil
rupture as well as settlement.

Embankment
height

A freeboard above the design bounce
height shall be included. Where space is
limited, a net fence may be used to extend
the height of the embankment so that it
can catch the infrequent higher bounce
rock or larger volume without substantially
increasing the footprint of the structure.

Embankment
width

The embankment width is governed by a
minimum top crest width of 3.3 feet (1 m),
with a minimum width at impact center
height of 2 times the penetration depth
and 5 times the extrusion length.

Upslope face

The upslope face angle should be as steep
as possible to minimize the potential for
blocks to roll up and over the structure. The
potential for a block to shatter should be
considered in the selection of the upslope
facing material.

Materials

Upslope ditch

This may be incorporated into the design
and may include a layer of energyabsorbing material as cushion. The upslope
profile change shall be considered for the
rockfall simulations.

Access and
maintenance
road

This should be incorporated to allow for
regular maintenance, including removal
of small debris or fallen rocks from behind
the embankment. The geometry of the
embankment should allow access for
equipment suitable for rock removal.

Drainage

Drainage through and around the
structure shall be considered to minimize
the potential for ponding, erosion and
instability issues. It needs to be considered
also if an upslope ditch is included.

Facing type

*	 Internal stability of embankment
(static and seismic analysis)
*	 External stability of slope and
embankment (static, seismic
and impact loading)
*	 Global stability of slope and
embankment (static, seismic
and impact loading)

The embankment deformation depends
also on the type of facing selected (e.g.,
wrap-around, gabions, rigid wood,
pneumatic tires, geocells, etc.).
Selection of the reinforcement must be
carefully considered. According to the
Rimoldi-Brusa method, reinforcement
can be made of steel or geosynthetic.
The following shall be evaluated:

Facing of the embankment (type, ease
of repair); backfill materials (e.g., friction
angle gradation, min/max particle
size, permeability, pH); geosynthetic
reinforcement (or steel mesh/strips);
construction and QA/QC equipment.
The following stability analyses should
be performed:

Stability
analyses

Durability and
maintenance

The embankment facing shall be durable
to resist environmental exposure and
potential minor impacts. It should be
easily patched under the SLS condition or
reconstructed in the affected section under
the ULS condition (designed impact event).
Reinforced RPEs can benefit from the easy
maintenance given by the reinforced
soil technique.

*	 Type of reinforcement (straps, geogrid,
geotextile, steel mesh, etc.)

Geosynthetic
selection

*	 Ultimate tensile strength and strength
at low deformation (2%)
*	 Angle of distribution given by the
inclusion of the reinforcement within
the earth embankment
*	 Number of reinforcements involved
during boulder impacts and
rockfall events
*	 Behavior of transversal and
longitudinal reinforcements
*	 Direct shear and pull-out
of the reinforcement

*	 Dynamic resistance to penetration
on the upslope face
*	 Dynamic resistance to extrusion
of the downward face

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Geosynthetics April/May 2021

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