E3S Web of Conferences 415, 06003 (2023)
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https://doi.org/10.1051/e3sconf/202341506003

Modelling flow-landslides impact against protection structures
Sabatino Cuomo1*
1Geotechnical Engineering Group (GEG), Department of Civil Engineering, University of Salerno, Italy

Abstract. Dynamic impact of flow-like landslides against protection structures calls for a soundunderstanding of the interaction mechanisms. In fact, despite a large variety of flow-landslides, there is also
a significant availability of several types of protection works and many different modelling approaches,
which have been customized to the specific classes of flow-landslides and protection structurers. Someremarks are reported below in a design-oriented engineering framework.

1 Introduction
Independent on the landslide type, the site-specific geoenvironmental context and the triggering mechanisms
always play a role. Among the most destructive gravitydriven mass movements there are flow-like landslides,
which can be mainly grouped in two main classes: i)channelised and ii) unchannelised. The former ones arecontrolled by both slope morphology and soil properties,while the latter ones can be even more complex as thepropagation path itself is the outcome of the propagation
mechanisms. Another key issue concerns the presence(or not) of boulders and the amount of rock debris. In
fact, the impact of boulders against protection structures
is highly destructive. On the other hand, the propagationof so-called flowslides is typically related to the featuresof the landslide body formed by liquefied soils. Even
more, the case of recurrent phenomena (e.g., annual orseasonal debris flows inside the same channel or ravine)
must be distinguished by those cases of first-failure
landslides, which occur and propagate only once in agiven area.
The previous differences are fundamental for: i) thetype of usable protection structures, ii) the landslidestructure interaction mechanisms.

2 Protection works and mechanisms
In many cases, the use of control works is one of the few
landslide mitigation options usable to protect structuresand infrastructures. Sometimes, the protection works areinstead part of a more comprehensive landslide risk
mitigation strategy including hazard/risk zoning, slope
stabilization interventions and early warning systems.
Many of the mitigation measures are designed tointercept and contain landslide debris in order to provide
protection to developments on slope or at hill toes. It
entails landslide resisting barriers and debris straining
structures. On the other hand, some of the mitigation
measures regulate the landslide debris runout processe.g., impediments along landslide debris flow path
which aim to achieve dissipation of debris kinetic
energy and to promote deposition of landslide debris.
According to this rationale, landslide risk mitigation
measures can be classified into two groups: i) flow
control measures and ii) protection measures. The firstgroup includes: transport channels, check dams, debris
flow impediment and straining structures, grillstructures, deflection structures, among others. thesecond group contains, for instance, debris-resistingbarriers, debris retention basins, debris flow sheds. A
complete description of those several options isavailable in the scientific literature, while some remarks
are provided below especially with reference to thelandslide-structure interaction mechanisms.
In fact, it is useful stressing that flow control
measures are engineering works constructed on thelandslide propagation path and they aim to regulate thelandslide debris runout process. Particularly, thoseworks are used to retard the rate of debris transportation
and reduce the active volume of the landslide debris.
Conversely, protection measures are usually constructed
at hill toe, and they are expected to retain some/all thelandslide debris and to prevent damages to development.
The landslide-structure interaction mechanisms areintimately related to the type and geometry of protection
work. (1) For instance, transport channels must ensure
the passage of debris surges down a pre-determined
path, without blockage or overflowing (Hungr et al,1987; Kang, 1996). (2) On the contrary, check dams
allow stormwater flow, as well as drainage of waterfrom the solid material entrapped behind the dam. (3)Interestingly, built as array of columns, the baffles areoften used to spread the flow (Cosenza et al, 2006) or
behind a debris-resisting barrier as a sacrificial structure
to screen out boulders for design robustness (Kwan et al,2018). (4) Debris-straining structures are measures withopenings designed to trap stony landslide debris,
including boulders, from a debris flow. Examples areslit-, cell-, or grid-structures. (5) On the contrary,“dewatering screens”, which are horizontal grill* Corresponding author: scuomo@unisa.it© The Authors, published by EDP Sciences. This is an open access article distributed under the terms of the Creative Commons Attribution License 4.0(https://creativecommons.org/licenses/by/4.0/).

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structures, allows the draining of the debris to slow it
down and consequently promotes debris deposition
through consolidation. (6) Deflection structures are used
to divert debris flows away from the highly vulnerable
areas towards a less steep topography, where the debris
runout velocity reduces, and debris deposition isinitiated. (7) Debris-resisting barriers are generally
constructed near the distal end of a drainage line as aterminal barrier in order to minimize the run-up heightand debris impact loading on the barrier. Rigid barriers(typically concrete dams or earthfill embankments) can
resist high impact load from the debris. Flexible barriers
are instead built using steel wire nets and are subject tolarge deformation when they intercept landslide debris.
(8) Debris retention basins are usually constructed at thedeposition zone where the ground profile is relatively
gentle, and a sufficient area is available for debris flow
to slow down and deposit.

analytical model for evaluating the deflection of aflexible barrier (a net fixed to the ground) through thevalidation against experimental results of centrifuge
tests. Ng et al. (2021) examined the case of dual barriers.
Recently, Cuomo et al. (2022) proposed ananalytical model based on inelastic collision approach
applied to a deformable landslide body impacting
against a movable and deformable earthfill barrier; Di
Perna et al. (2022) proposed an enriched empiricalapproach for impact loading and landslide energy
release. Both approaches were calibrated and validated
through Material Point Method simulations.
Nevertheless, landside physical modelling is still avaluable tool, and recent experiences in centrifuge orlarge flume facilities allow collecting meaningful
insights about the landslide-structure interaction
mechanisms, for instance for rigid and flexible barriers(Song et al., 2017; Choi et al., 2015).
Dr. Julian Kwan (Geotechnical Engineering Office, HongKong, China), as well as Dr. Angela Di Perna (University ofSalerno, Italy) and Dr. Mario Martinelli (Deltares, Delft,Netherlands) are respectively acknowledged for the helpful
discussions and the support in numerical modelling.

3 Modelling approachesNumerical modelling is the most used option to tackle
the analysis of Landslide-Structure Interaction (LSI).
Examples of Discrete Element Method (DEM) are
reported by Leonardi et al. (2016), Calvetti et al. (2017)
and Shen et al. (2018) or continuum mechanics models
based on Eulerian methods (Moriguchi et al. 2009),
Lagrangian particle-based methods such as SmoothedParticle Hydrodynamics (SPH) (e.g. Bui and Fukagawa2013), Particle Finite Element Method (PFEM) (e.g.
Idelsohn et al. 2006), Finite Element Method with
Lagrangian integration points (FEMLIP) (e.g., Cuomoet al. 2013), Material Point Method (MPM), (Ceccato etal., 2018) or coupled Eulerian-Lagrangian methods(Jeong and Lee 2019).
Several other numerical methods exist since years(Rabczuk and Belytschko, 2004) and meshfree methods
are becoming very popular. However, the solid-fluidhydro-mechanical coupling and the role of theinterstitial fluid in the landslide-structure interaction
have been considered only in recent times. For instance,
the impact behaviour of saturated flows against rigidbarriers was simulated through MPM analyses ofcentrifuge test results (Cuomo et al., 2021a).
Analytical models have been also used to investigate
the LSI for various cases. Yong et al. (2019) proposed
an analytical solution for estimating the sliding of abarrier under the impact of a boulder. In this case, thecolliding bodies are both assumed as rigid, and theimpact is studied through the elastic collision principles.
However, such method cannot be applied for instance tothe case of a flow-like landslide impacting a Deformable
Geosynthetics-Reinforced Barrier (DGRB), i.e., anembankment made of coarse-grained soil layers
reinforced by geogrids (Cuomo et al., 2020b). Li et al.
(2021) proposed an analytical model to estimate thepeak impact pressure that a debris flow exerts on a rigidbarrier. Such model has the strength of being validated
by data encompassing a wide range of distinct flow
regimes, relative to real-scale observations of debris
flows, small-scale experiments and recent coupled
CFD-DEM simulations. Song et al. (2021) obtained an

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