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Abstract

Debris flows are a type of mass movement characterized by high velocities and rapid evolution over time. These features, together with their capability to transport huge amounts of material, make them one of the most hazardous natural processes for both human lives and man-made structures. Therefore, a timely and effective monitoring activity plays a major role in any mitigation and early warning action connected with debris flow, such as alert messages dissemination and road closures. This paper deals with the development of a new automatic system named Gflow Safety Network (GSN), designed to be installed on flexible debris flow barriers with the objective to monitor the structure behavior with a real time approach. The main component of the system (called Gflow module) integrates an accelerometer and an electronic board, and it is able to identify an impact that generates an acceleration value higher than a predefined threshold. In this scenario, the system activates the accelerometer sensor integrated in the module and triggers every other monitoring device installed on-site to acquire information on the ongoing phenomenon. A series of impact tests were performed on a prototype installed on a flexible structure, in order to verify the initialization time of the accelerometer sensor after the first threshold overcoming. The outcomes evidenced the good performances of the Gflow module, which was able to record the event following the first impact on the test structure.
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Transportation Research Procedia 55 (2021) 1783–1790
2352-1465 © 2021 The Authors. Published by ELSEVIER B.V.
This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0)
Peer-review under responsibility of the scientific committee of the TRANSCOM 2021: 14th International scientific conference on
sustainable, modern and safe transport
10.1016/j.trpro.2021.07.169
10.1016/j.trpro.2021.07.169 2352-1465
© 2021 The Authors. Published by ELSEVIER B.V.
This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0)
Peer-review under responsibility of the scientic committee of the TRANSCOM 2021: 14th International scientic conference
on sustainable, modern and safe transport
Available online at www.sciencedirect.com
ScienceDirect
Transportation Research Procedia 00 (2021) 000000
www.elsevier.com/locate/procedia
© 2021 The Authors. Published by ELSEVIER B.V.
This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0)
Peer-review under responsibility of the scientific committee of the TRANSCOM 2021: 14th International scientific conference on sustainable,
modern and safe transport
14th International scientific conference on sustainable, modern and safe transport
Development and Preliminary Tests of a Low-Power Automatic
Monitoring System for Flexible Debris Flow Barriers
Roberto Savia, Alessandro Vallettaa *, Andrea Carrib, Edoardo Cavalcaa, Andrea
Segalinia
aUniversity of Parma, Department of Engineering and Architecture, Parco Area delle Scienze 181/a, 43124 Parma, Italy
bASE Advanced Slope Engineering S.r.l., Parco Area delle Scienze 181/a, 43124 Parma, Italy
Abstract
Debris flows are a type of mass movement characterized by high velocities and rapid evolution over time. These features, together
with their capability to transport huge amounts of material, make them one of the most hazardous natural processes for both human
lives and man-made structures. Therefore, a timely and effective monitoring activity plays a major role in any mitigation and early
warning action connected with debris flow, such as alert messages dissemination and road closures. This paper deals with the
development of a new automatic system named Gflow Safety Network (GSN), designed to be installed on flexible debris flow
barriers with the objective to monitor the structure behavior with a real time approach. The main component of the system (called
Gflow module) integrates an accelerometer and an electronic board, and it is able to identify an impact that generates an acceleration
value higher than a predefined threshold. In this scenario, the system activates the accelerometer sensor integrated in the module
and triggers every other monitoring device installed on-site to acquire information on the ongoing phenomenon. A series of impact
tests were performed on a prototype installed on a flexible structure, in order to verify the initialization time of the accelerometer
sensor after the first threshold overcoming. The outcomes evidenced the good performances of the Gflow module, which was able
to record the event following the first impact on the test structure.
© 2021 The Authors. Published by ELSEVIER B.V.
This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0)
Peer-review under responsibility of the scientific committee of the TRANSCOM 2021: 14th International scientific conference
on sustainable, modern and safe transport
Keywords: Debris flow; Monitoring; Early Warning; Accelerometer
* Corresponding author. Tel.: +0-000-000-0000 ; fax: +0-000-000-0000 .
E-mail address: alessandro.valletta@unipr.it
Available online at www.sciencedirect.com
ScienceDirect
Transportation Research Procedia 00 (2021) 000000
www.elsevier.com/locate/procedia
© 2021 The Authors. Published by ELSEVIER B.V.
This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0)
Peer-review under responsibility of the scientific committee of the TRANSCOM 2021: 14th International scientific conference on sustainable,
modern and safe transport
14th International scientific conference on sustainable, modern and safe transport
Development and Preliminary Tests of a Low-Power Automatic
Monitoring System for Flexible Debris Flow Barriers
Roberto Savia, Alessandro Vallettaa *, Andrea Carrib, Edoardo Cavalcaa, Andrea
Segalinia
aUniversity of Parma, Department of Engineering and Architecture, Parco Area delle Scienze 181/a, 43124 Parma, Italy
bASE Advanced Slope Engineering S.r.l., Parco Area delle Scienze 181/a, 43124 Parma, Italy
Abstract
Debris flows are a type of mass movement characterized by high velocities and rapid evolution over time. These features, together
with their capability to transport huge amounts of material, make them one of the most hazardous natural processes for both human
lives and man-made structures. Therefore, a timely and effective monitoring activity plays a major role in any mitigation and early
warning action connected with debris flow, such as alert messages dissemination and road closures. This paper deals with the
development of a new automatic system named Gflow Safety Network (GSN), designed to be installed on flexible debris flow
barriers with the objective to monitor the structure behavior with a real time approach. The main component of the system (called
Gflow module) integrates an accelerometer and an electronic board, and it is able to identify an impact that generates an acceleration
value higher than a predefined threshold. In this scenario, the system activates the accelerometer sensor integrated in the module
and triggers every other monitoring device installed on-site to acquire information on the ongoing phenomenon. A series of impact
tests were performed on a prototype installed on a flexible structure, in order to verify the initialization time of the accelerometer
sensor after the first threshold overcoming. The outcomes evidenced the good performances of the Gflow module, which was able
to record the event following the first impact on the test structure.
© 2021 The Authors. Published by ELSEVIER B.V.
This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0)
Peer-review under responsibility of the scientific committee of the TRANSCOM 2021: 14th International scientific conference
on sustainable, modern and safe transport
Keywords: Debris flow; Monitoring; Early Warning; Accelerometer
* Corresponding author. Tel.: +0-000-000-0000 ; fax: +0-000-000-0000 .
E-mail address: alessandro.valletta@unipr.it
1784 Roberto Savi et al. / Transportation Research Procedia 55 (2021) 1783–1790
2 Savi et. al. / Transportation Research Procedia 00 (2021) 000000
1. Introduction
Debris flows are extremely rapid, flow-like mass movements involving a saturated, unsorted mixture of granular
soils, organics, and other debris Hungr (2013). These features, together with their ability to travel great distances,
make this typology of landslide particularly devastating, with a single event potentially able to destroy entire c ities
and cause heavy human losses Dowling and Santi, (2014). Moreover, even more social-economic resources are needed
in the after-event management, including reconstruction, livelihood of victims, and recovery of the disaster area Liu
et al., (2009). This is especially important for what concern transport infrastructures, which can sustain both direct
damage involving the road and associated structures, and consequential damages such as effect of delays, detours, and
reduced level of business activities Fraštia et al., (2019); Milne et al. (2009); Winter et al. (2014); Winter and
Bromhead, (2012). Because of this, several mitigation strategies have been developed over the years, including both
passive and active measures to reduce the risk associated with these events Jakob and Hungr, (2005); Vagnon et al.,
(2020); Vagnon (2020).
During the last decades, several authors have addressed the development and application of different monitoring
and early warning systems specifically designed for debris flow events. Hungr et al. (1987) identified three categories
to describe the features of different warning systems, which could rely on correlation with the behavior of triggering
parameters such as rainfalls (Arattano and Marchi, 2008), direct measurement of the debris flow event McArdell et
al. (2007), or monitoring of the phenomenon effects on buildings and structures after its occurrence Hungr et al.,
(1987). In particular, Early Warning Systems (EWS) intended to disseminate alert messages at the event occurrence
could be aimed to observe the phenomenon during its evolution, or they could be developed for the direct monitoring
of previously installed mitigation structures (e.g., debris flow barriers). The interaction with structural protection
measures is a key aspect in the analysis of these phenomena, and several different studies have been carried out on
this topic by exploiting in-situ observations and numerical modelling (e.g. Ferrero et al. (2010); Vagnon et al. (2017,
2018); Chen et al. (2019); Marchelli and De Biagi (2019). Early warning and monitoring applications have benefited
significantly from the several technological innovations that were introduced during recent years in the geotechnical
field. Notably, the introduction of automatic devices and the improvement of remote communication between sensors
and control units allowed to develop real time and near-real time monitoring systems with the ability to provide an
accurate and timely description of the ongoing event. On the other hand, devices able to record data with high sampling
frequencies require a careful evaluation of the power supply unit design, since an underpowered system could be
unable to continue properly the monitoring activity, with potentially devastating consequences in case of an undetected
event.
This paper describes a monitoring and early warning system based on the Internet of Natural Hazards (IoNH)
approach Segalini et al. (2019), and specifically developed to be installed on flexible debris flow barrier. The system
exploits several different sensors in order to identify the occurrence of a potentially critical event and achieve a near-
real time monitoring of the structure behavior. In particular, this paper is going to focus on the development of the
component dedicated to the activation of the entire system after the detection of a debris flow in close proximity to
the barrier. The main objective is to verify the ability of the system to trigger the monitoring activity in a sufficiently
short time period in order to follow accurately the event evolution over time.
2. Materials and Methods
2.1. Monitoring system description
As underlined before, a reliable power source is a key component of each acquisition and communication system
Reid et al. (2008). This is especially relevant when dealing with monitoring devices installed in remote areas, where
fixed connections to a power line are often unavailable. For this reason, automatic monitoring system usually rely on
a battery-supplied structure with the integration of a solar panel to recharge the power unit.
The proposed system, named Gflow Safety Network (GSN), was developed to provide a near-real time automatic
monitoring system for flexible debris flow barriers, featuring low power consumption and the ability to trigger the
activation of all connected devices at the occurrence of a critical event. Moreover, the GSN structure would allow to
Roberto Savi et al. / Transportation Research Procedia 55 (2021) 1783–1790 1785
Savi et. al. / Transportation Research Procedia 00 (2021) 000000 3
integrate multiple sensors measuring different parameters, in order to have a complete description of the ongoing
phenomenon.
The core of the GSN system is the Gflow module, designed to be placed directly on the monitored structure in
order to detect the accelerations experienced by the debris flow barrier. This element consists of a certified IP68 metal
box (dimensions: 12.5 x 9.0 x 6.0 cm) fixed to a two-plate system specifically designed for its installation (Fig.
1aChyba! Nenašiel sa žiaden zdroj odkazov.). The module integrates an accelerometer (ADXL335) and an
electronic control board, while the power supply is provided by a 3.6 V lithium battery connected to a charge controller
and a solar panel placed on the upper part of the metal box.
The Gflow module is able to switch between two operating modes, depending on the data recorded by the
accelerometer. The standard configuration is defined Low Power Mode, which is intended to minimize power
consumption by activating only the essential components of the electronic board. The transition into Operational Mode
is triggered by the overcoming of a predefined acceleration threshold, related to the electrical tension values measured
on two analog ports located on the board. These data correspond to the accelerometer output along the X and Y axes
respectively, according to the configuration presented in Fig. 1b. Alternatively, Operational Mode can be activated
with a user-defined frequency, which can also be set from remote after the system installation. While in this state, the
Gflow module samples 150 acceleration data and compares them with a second software-based threshold. If this level
is not reached, the system transmits the acquired
dataset containing information on the steel net rotation and the module status. On the other hand, the threshold
overcoming additionally triggers the reading of any other monitoring device connected to the GSN system, such as
remote cameras, to acquire more information on the event responsible of the system activation.
2.2. System activation tests
The system ability to activate the monitoring sensors in correspondence of an event involving the barrier is one of
the most important processes in the GSN application for early warning purposes. In particular, it is fundamental to
have a time interval between the impact on the structure and the triggering of system as short as possible, in order to
be able to acquire information on the debris flow interaction with the barrier.
For this reason, preliminary tests performed on the Gflow module involved the initialization time assessment by
installing the device on a flexible steel net and simulating a sudden impact on the structure. Data recorded by the
sensors integrated in the module were matched with those acquired by another accelerometer (PCB356A16), installed
on the same structure and recording the event with a continuous approach. The comparison between the two datasets
allowed to identify the point where the Gflow started the sampling process, which corresponds to the transition
between Low Power and Operational Mode. Taking as a reference the start of the load application, which can be
Fig. 1. a) Gflow module protoype, fixed to the installation plates; b) Graphical render representing the Gflow installation and axes orientation
with respect to the debris flow barrier.
(a) (b)
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assessed thanks to the second accelerometer, it was possible to identify the time needed by the Gflow to enter
Operational Mode and start recording the event.
Fig. 2 describes the setup used to perform the initialization time test, which entailed a total of three different
configurations depending on the number of load application points actively involved in each setup. The Gflow
prototype was installed 2.60 m from the right anchor point of the structure, realized with two steel ropes and a triple-
torsion metal net. The impact was simulated by releasing a 5kg weight connected to the structure with a 1.10-metre
long steel wire. The starting position of each weight before being dropped matched the height at which the structure
was installed. Moreover, a digital camera (Canon EOS 5D) was used to record the tests outcomes in order to assess
the weight impact velocity on the structure. Table 1 summarizes the three different configurations and the different
load application points involved.
Table 1. Load configurations of the three tests performed on the Gflow module
Load Point A
Load Point B
Load Point C
x
x
x
x
x
x
3. Results and Discussion
Because of the general setup of the performed test, data elaboration involved the comparison of acceleration values
recorded along the X-axis of for both sensors. The analysis was carried out with the Signal Processing Toolbox
developed by Mathworks® and followed the steps reported below:
Extraction of the signal recorded by the PCB356A16 accelerometer along the X-axis for a time duration of 1.5
seconds;
Extraction of the signal recorded by the ADXL335 accelerometer along the X-axis and alignment of the two
datasets;
Fig. 2. Position of the two accelerometers and three load application points on the test structure.
Roberto Savi et al. / Transportation Research Procedia 55 (2021) 1783–1790 1787
Savi et. al. / Transportation Research Procedia 00 (2021) 000000 5
Identification of the time
0
corresponding to the first reading above the analog threshold of 0.1 g, recorded by
the PCB356A15 accelerometer;
Identification of the time 1 corresponding to the first reading performed by the Gflow module;
Initialization time evaluation, as  = 1− 0.
3.1. CC1 configuration
The first test involved the release of a 5 Kg weight in correspondence of the Load Point A. Fig. 3a displays the
position and velocity reached by the ballast, from its initial release to the point of complete extension of the steel rope.
From this plot it is possible to note that the weight achieved a maximum velocity equal to 4.7 m/s recorded at 1.12 m
from the release point. After this point, the reaction force applied by the structure leads to a deceleration, and the next
measured velocity is 3.7 m/s.
The comparison between datasets recorded by the two different accelerometers is reported in Fig. 3b. In particular,
it is possible to observe the main impact recorded by the PCB356A16 accelerometer, leading to an overcoming of the
predefined threshold at 0=138.19 ms. Following peaks recorded after this event are caused by the elastic response of
the steel net, which induces a rebound effect on the dropped weights with a subsequent load application. By comparing
the recorded datasets it’s possible to observe the good correspondence between the two datasets recorded by the
accelerometers after the Gflow module activation, which happened at 1=179.00 ms. As a result, the initialization time
observed in the CC1 configuration is equal to 40.81 ms.
It is worth noting that the difference between the two datasets in correspondence of acceleration peaks derives from
the different range of the two sensors. In fact, the ADXL335 accelerometer has a range of ±5 g, so it is not suitable to
measure higher accelerations.
3.2. CC2 configuration
This configuration involved the release of two 5 kg weights from the same quote, in order to obtain an impact as
simultaneous as possible. The result of this procedure is reported in Fig. 4a, displaying the position in the vertical
Fig. 3. a) Position and velocity evolution over time referring to the weight released in the load application involved in the CC1 configuration; b)
Acceleration signal recorded by the two accelerometers installed on the structure in the CC1 configuration, with a magnified
representation of the
first impact identified.
(a) (b)
1788 Roberto Savi et al. / Transportation Research Procedia 55 (2021) 1783–1790
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direction and the velocity over time of the ballasts used for this test. It is possible to notice that, in both cases, the
maximum velocity was reached at the same time and amounts to 4.4 m/s.
As in the previous configuration, the acceleration signal (Fig. 4b) evidences the main event caused by the impact,
followed by a series of minor peaks associated with the elastic response of the test structure. However, it is possible
to observe that the Gflow module was able to measure correctly the acceleration variation, as confirmed by the
comparison with data recorded by the other device. In this case, the impact was identified at 0=201.76 ms when the
acceleration values overcame the predefined threshold. Moreover, the Gflow module sampled the first value of the
dataset at 1=248.00 ms, leading to an initialization time of 46.24 ms.
3.3. CC3 configuration
In the last configuration, the test includes the release of three 5 Kg weights located at load application points A, B,
and C. As can be observed in Fig. 5a, the ballasts moved simultaneously with a minor deviation evidenced by the
element located in position C. However, all weights reached the maximum velocity at the same time instant, thus
generating a uniform impact in the structure. Peak velocities for CC3 configuration range from 4.6 m/s to 4.9 m/s.
Fig. 4. a) Position and velocity evolution over time referring to the weight released in the load application involved in the CC2 configuration;
b) Acceleration signal recorded by the two accelerometers installed on the structure in the CC2 configuration, with a magnified representation
of the first impact identified.
Fig. 5. a) Position and velocity evolution over time referring to the weight released in the load application involved in the CC3 configuration; b)
Acceleration signal recorded by the two accelerometers installed on the structure in the CC3 configuration, with a magnified representation o
f the
first impact identified.
(a) (b)
(a) (b)
Roberto Savi et al. / Transportation Research Procedia 55 (2021) 1783–1790 1789
Savi et. al. / Transportation Research Procedia 00 (2021) 000000 7
The acceleration signal represented in Fig. 5b displays two major events, probably related to the slightly different
release time of the ballasts. Both events exceed the predefined threshold, so the first impact was responsible of the
activation of the Gflow module, which correctly recorded also the following acceleration variations. In particular, the
threshold overcoming happened at 0=180.80 ms, as recorded by the PCB365A16 accelerometer, while the first value
measured by the ADXL335 sensor was obtained at 1=231 ms. Thus, the initialization time resulting from the CC3
configuration is equal to 50.20 ms.
By taking into account the results obtained in all different tests, it results that the average time interval between the
detection of a threshold overcoming and the initialization of the Gflow module is 45.75 ms. Table 2 summarizes the
tests outcomes for all three configurations.
Table 2. Results obtained for the three different impact test configurations
Test configuration
Threshold overcoming 0 [ms]
Gflow module activation 1 [ms]
Initialization time  [ms]
CC1
138.19
179.00
40.81
CC2
201.76
248.00
46.24
CC3
180.80
231.00
50.20
4. Conclusions
Debris flow are one of the most dangerous types of mass movements. Featuring high velocities and long runout
distances, they are responsible of causing massive damages to buildings and transport structures, also leading to
significant human losses due to their rapid evolution. For these reasons, debris flow monitoring and early warning
activities are essential to prevent and mitigate these hazards. A large number of different approaches have been
introduced over the years, integrating different sensors for the monitoring of the event evolution and its influence on
mitigation structures.
This paper focuses on the preliminary tests performed during the development of a new monitoring system named
Gflow Safety Network (GSN), specifically designed to be installed on flexible debris flow barriers. The main goal of
the system it the identification of an impact on the structure and the activation of any connected monitoring device, in
order to acquire useful information on the event and its effect of the protection structure with a near-real time approach.
The Gflow module is the primary component of the GSN system, and it has the task to identify the impact after the
overcoming of a predefined acceleration threshold. It integrates an accelerometer and an electronic board, while a 3.6
V lithium battery provides the power supply.
In order to evaluate the initialization time of the Gflow module, a series of tests were performed by installing a
prototype version of the device on a flexible structure. The impact intended to trigger the module was simulated with
three different configurations, each of them involving a different number of load application points. The tests were
performed by evaluating the time interval between the first threshold overcoming, identified thanks to another
accelerometer operating with a continuous reading approach, and the first value sampled by the Gflow module. Results
obtained by performing these tests evidenced the fast response of the sensor to the impact experienced by the structure.
In particular, the mean initialization time value deriving from the three test configurations is equal to 45.75 ms. In a
real case scenario, such a rapid start-up of the Gflow module would be able to guarantee a timely activation of all
instrumentation installed on-site, thus managing to obtain useful information concerning the event and to disseminate
alert messages depending of the monitoring data sampled by the instrumentation.
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This paper discusses the applicability and the limitations of an approach to the limit states design of flexible barrier in which the soil/rock strength are factored as required in the European construction code. It shows as this approach has different implications if it is applied to the same kind of structure when loaded by different phenomena (rockfall and debris flow in particular). Flexible barriers are common countermeasures to protect from rockfall hazard and to restrain debris flow events. Even if an intense scientific production has demonstrated the difference between the two phenomena, the protection systems are still often designed in the same way. Additionally, the Eurocode 7 (EC7), which is the European Standard concerning geotechnical design, has not been conformed to these kinds of structures and consequently a relationship between the reliability of the system and the partial factors does not exist. Since most of the parameters that rule these systems are not even considered in the code, the Authors propose the study of two cases, in which rockfall and debris flow occur, respectively, to analyse the applicability and the limitations of EC7 principles to design the suitable kind of structure.
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Debris flows occur in mountainous areas characterized by steep slope and occasional severe rainstorms. The massive urbanization in these areas raised the importance of studying and mitigating these phenomena. Concerning the strategy of protection, it is fundamental to evaluate both the effect of the magnitude (that concerns the definition of the hazard), in terms of mobilized volume and travel distance, and the best technical protection structures (that concerns the mitigation measures) to reduce the existing risk to an acceptable residual one. In particular, the mitigation measure design requires the evaluation of the effects of debris flow impact forces against them. In other words, once it is established that mitigation structures are required, the impacting pressure shall be evaluated and it should be verified that it does not exceed barrier resistance. In this paper, the author wants to focus on the definition and the evaluation of the impacting load of debris flows on protection structures: a critical review of main existing models and equations treated in scientific literature is here presented. Although most of these equations are based on solid physical basis, they are always affected by an empirical nature due to the presence of coefficients for fitting the numerical results with laboratory and, less frequently, field data. The predicting capability of these equations, namely the capability of fitting experimental/field data, is analysed and evaluated using ten different datasets available in scientific literature. The purpose of this paper is to provide a comprehensive analysis of the existing debris flow impact models, highlighting their strong points and limits. Moreover, this paper could have a practical aspect by helping engineers in the choice of the best technical solution and the safe design of debris flow protection structures. Existing design guidelines for debris flow protection barrier have been analysed. Finally, starting from the analysis of the hydro-static model response to fit field data and introducing some practical assumptions, an empirical formula is proposed for taking into account the dynamic effects of the phenomenon.
Article
In the European Union since 2010, the design of any type of structures must comply with EN-1997 Geotechnical Design (CEN 2004) (EC7) referring to engineering projects in the rock mechanics field. However, the design of debris flow countermeasures in compliance with EC7 requirements is not feasible: EC7 uses partial safety factors for design calculations, but safety factors are not provided for phenomena such as debris flows and rock falls. Consequently, how EC7 can be applied to the design of debris flow barriers is not clear, although the basic philosophy of reliability-based design (RBD), as defined in EN1990 (CEN 2002) and applicable to geotechnical applications, may be a suitable approach. However, there is insufficient understanding of interactions between debris flows and structures to support RBD application to debris flow barrier design, as full-scale experimental data are very limited and difficult to obtain. Laboratory data are available but they are governed by scale effects that limit their usefulness for full-scale problems. The article describes an analysis, using the first-order reliability method (FORM), of two different datasets, one obtained through laboratory experiments and the other reflecting historical debris flow events in the Jiangjia Ravine (China). Statistical analysis of laboratory data enabled a definition of the statistical distributions of the parameters that primarily influence debris flow and barrier interactions. These statistical distributions were then compared to the field data to explore the links between flume experiments and full-scale problems. This paper reports a first attempt to apply RBD to debris flow countermeasures, showing how the choice of the target probability of failure influences the barrier design resistance value. An analysis of the factors governing debris flows highlights the applicability and limitations of EN1990 and EN1997 in the design of these rock engineering structures.
Article
Debris flows are rapid gravity-driven flows of sediment-water mixture, which can be greatly destructive due to its huge volume, high velocity and large impact force. Check dam is essential protective structure for controlling debris flow. However, it is a challenging work to assess the interactions between debris flow and check dam, especially when involving complex topography and dam destruction. A numerical method was developed in this study to investigate the interactions between debris flow and check dam on three-dimensional terrain. The debris flow and check dam were simulated by Smoothed Particle Hydrodynamics (SPH) method and Finite Element Method (FEM), respectively. The method was validated by a dam break problem and a granular flow flume test. An actual debris flow event originated from failure of tailings dams on 19 July 1985 in Stava, Italy was simulated as an example. The results indicate that the proposed method is a practical tool to simulate the runout characteristics of debris flow (e.g., flow velocity, flow depth, impact area) and interactions between debris flow and check dam (e.g., impact force, destruction of check dam, interception by check dam). Given similar total dam volume, increasing the number of dams will improve the hazard mitigation effect. Moreover, it is recommended to construct dams in downstream area with straight channel. This study will contribute to a better understanding of the flow-structure interaction and is helpful for rational design of check dams.
Article
Debris flow is a transient phenomenon that causes large disasters. Retaining systems, whose design is still nowadays a crucial issue, can mitigate this risk. Multiple surges can arise during this phenomenon; thus, an accurate analysis might consider the impact force time histories rather than only its maxima. The aim of this work is to analyze the effects of the interaction between the debris and the barrier during one surging phenomenon. A discrete element model models the granular motion and the interaction between the debris and a rigid open barrier set at the end of the channel. The estimated interaction force time history is then used as input impact force for the dynamic structural analyses of the piles. A total of 12 different structural sections are adopted and the internal forces at the base are critically compared. It results that the first mode vibration period is the parameter that largely affects the behavior of the piles.
Article
This paper analyses an important aspect of the continuum numerical modeling of rapid landslides as debris flows: by using the same rheological parameter values, are the results, obtained with codes that implement the same constitutive equations but a different numerical solver, equal? In order to answer this question, the two numerical codes RASH3D and GeoFlow_SPH are here used to back-analyze the debris flow event occurred in the Nora stream (Northwestern Italian Alps) in October 2000. Comparison of results evidenced that the RASH3D best fit rheological values for the Nora event back analysis overestimated both the final depositional heights and the simulated flow velocities if used in GeoFlow_SPH. In order to obtain thickness values comparable with those measured in situ, it was necessary to re-calibrate GeoFlow_SPH rheological parameter values. In this way, with the exception of a larger lateral spreading of the sliding mass given by RASH3D, both thickness and velocity values were similar for the two numerical codes.
Chapter
A considerable amount of experience with engineering control of debris flow hazards has been gathered in British Columbia, Canada. A summary of this experience encompasses the entire spectrum of possible defensive measures. Passive measures include hazard mapping and zoning, the basic techniques of which are briefly described, and various types of warning systems that have been used with mixed success. Active defensive measures have been applied in the source areas, transportation zones, and deposition zones of debris flow-prone creek basins. The primary measures being applied at present in the source areas concentrate on controlling timber harvesting methods and encouraging reforestation. Engineered erosion control devices such as check dams and channel linings have thus far received limited use in British Columbia. In the transportation zone, design methods have been developed for training chutes and channels, deflecting dikes, diversions, adequate bridge openings and clearances, and overhead debris chutes. The most widespread designs of defensive measures relate to the deposition zone (debris fan) of mountain streams and include inexpensive "open" deposition basins, as well as more sophisticated "closed" structures incorporating a controlled discharge section and a spillway. A number of examples of completed or proposed structures are described and discussed from the point of view of design methodology.
Article
Debris flows cause significant damage and fatalities throughout the world. This study addresses the overall impacts of debris flows on a global scale from 1950 to 2011. Two hundred and thirteen events with 77,779 fatalities have been recorded from academic publications, newspapers, and personal correspondence. Spatial, temporal, and physical characteristics have been documented and evaluated. In addition, multiple socioeconomic indicators have been reviewed and statistically analyzed to evaluate whether vulnerable populations are disproportionately affected by debris flows. This research provides evidence that higher levels of fatalities tend to occur in developing countries, characterized by significant poverty, more corrupt governments, and weaker healthcare systems. The median number of fatalities per recorded deadly debris flow in developing countries is 23, while in advanced countries, this value is only 6 fatalities per flow. The analysis also indicates that the most common trigger for fatal events is extreme precipitation, particularly in the form of large seasonal storms such as cyclones and monsoon storms. Rainfall caused or triggered 143 of the 213 fatal debris flows within the database. However, it is the more uncommon and catastrophic triggers, such as earthquakes and landslide dam bursts, that tend to create debris flows with the highest number of fatalities. These events have a median fatality count >500, while rainfall-induced debris flows have a median fatality rate of only 9 per event.