“Debris Flow Risk mitigation by the means of rigid and flexible barriers.
Experimental tests and impact analysis”
Anna Maria Ferrero, Luigi Canelli
Università degli Studi di Parma
Giuseppe Mandrone
Università degli Studi di Torino
Rif. Progetto ICE D.R. 975 del 26/11/2009
RATIONALE AND OBJECTIVES
Despite there is no connection between debris flows frequency and global warming in the Alps,
recent studies have concluded that debris flows are significantly increasing at the margin of
glaciers (Chiarle et al. 2006)
These events are among the largest in Italian Alps.
Recently in order to control and mitigate debris and mud flows events, flexible barriers (such as
net barriers) have been used. Noteworthy are the similarities between these barriers and the
protections used for rock fall events. (Ferrero et al. 2010, Wendeler et al. 2008)
For this typology of barriers there is no specific regulation, experimental results on debris flows
impact on structures are controversial.
Experimental tests
Full scale tests
Numerical Modelling
Understand properly the interaction
of Debris Flows with barriers
and define a solid and easy to use design method
Università degli Studi di Parma
Progetto ICE D.R. 975 del 26/11/2209
EXPERIMENTAL METHOD
Level trasducers
0.400 m^3
35 fps cameras
Load cells
Rectangular flume (dim. 4 x 0.4 x 0.7 m, inclined 30°)
Bottom dumping hopper
Barrier (rigid or flexible)
Università degli Studi di Parma
Progetto ICE D.R. 975 del 26/11/2209
EXPERIMENTAL METHOD
Properties of the mixture
Flows of water saturated sand
Università degli Studi di Parma
Progetto ICE D.R. 975 del 26/11/2209
d50 (m)
0.001
Фg (°)
30
ρs (kg/m3)
2550
ρf (kg/m3)
1000
ρm (kg/m3)
1930
υs
0.6
υf
0.4
hf (m)
0.02÷0.1
v (m/s)
1.8÷5.5
BARRIERS INSTALLED
Università degli Studi di Parma
Progetto ICE D.R. 975 del 26/11/2209
DATA ANALYSES AND FIRST RESULTS
Test analyses were conducted measuring:
1. Flow depth at each level trasducers
2. Dynamic Thrust using load cells
…estimating:
1. Flow velocity (using image analysis and level trasducers)
2. Froude number of the front Fr f 
3. Adimensional impact force
~
F
Università degli Studi di Parma
Progetto ICE D.R. 975 del 26/11/2209
v
ghg
Fmax
1
g m hg2
2
DATA ANALYSES AND FIRST RESULTS
and comparing the obtained value of the adimensional impact force with
the following formulations:
1. Momentum balance: F 
2. Hungr (1984):
 m v 2 A (vertical jet-like wave)
F  1.5  m v 2 A
3. Campania Region (After Sarno, 1998), Japan
F  mv2 A 
4. Armanini & Scotton (1993): F  4.5hmax A
1
 m gh f A
2
Adimensional Formulation
1.
2.
3.
Università degli Studi di Parma
Progetto ICE D.R. 975 del 26/11/2209
4.
~
F  2 Fr f2
~
F  3Fr f2
~
F  1  2 Fr f2
~
F 9
Rigid barrier perpendicular to the channel
600
y = 1.6222x2.1964
R² = 0.811
500
Adimensional Force
400
Measured Adimensional Force
Armanini & Scotton (1993)
300
Power tdline
Momentum balance
Hungr (1984)
200
100
0
0
2
4
6
8 di Parma
Università
degli Studi
Froude Number
Progetto ICE D.R. 975 del 26/11/2209
10
Rigid barrier in vertical position
600
y = 1.0282x2.5982
R² = 0.7959
500
Adimensional Force
400
Measured Adimensional Force
Armanini & Scotton (1993)
300
Power tdline
Momentum balance
Hungr (1984)
200
100
0
0
2
4
Froude Number
6
8
Università degli Studi di Parma
Progetto ICE D.R. 975 del 26/11/2209
10
Dynamic thrust loading due to
the impact of the peak of the sourge
(duration 2/10 s)
Impulsive load caused by the fall
of the reflected wave into the channel (1/40 s)
Università degli Studi di Parma
Progetto ICE D.R. 975 del 26/11/2209
Rigid filter barrier in vertical position
600
500
Adimensional Force
400
Measured Adimensional Force
Armanini & Scotton (1993)
300
Momentum balance
Hungr (1984)
200
100
0
0
1
2
3
4
Froude Number
5
6
Università degli Studi di Parma
Progetto ICE D.R. 975 del 26/11/2209
7
8
Net barrier vertical position
600
500
Adimensional Force
400
Measured adimensional force
Armanini & Scotton (1993)
300
Momentum balance
Hungr (1984)
200
100
0
0
1
2
3
4
Froude Number
5
6
7
Università degli Studi di Parma
Progetto ICE D.R. 975 del 26/11/2209
8
CONCLUDING REMARKS & FUTURE DEVELOPMENTS
Results have shown that even if empirical, Hungr’s formulation (1984) is a solid and easy to use
method for the estimation of the dynamic thrust of a debris flow.
For channelized flows it has to be taken into account the possibility of an impulsive force due to
the impact of the reflected wave into the channel.
Filter and flexible barrier do not cause this phenomenon.
More tests will be conducted, changing the characteristics of the mixture
and trying to evaluate the additional load due to
collisional force of a single boulder.
Real scale tests will be performed on a flexible net.
Università degli Studi di Parma
Progetto ICE D.R. 975 del 26/11/2209
Thank you for your attention!
Contacts:
[email protected]
[email protected]
Università degli Studi di Parma
Progetto ICE D.R. 975 del 26/11/2209