“Debris Flow Risk mitigation by the means of rigid and flexible barriers. Experimental tests and impact analysis” Anna Maria Ferrero, Luigi Canelli Università

“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

Università degli Studi di Parma Progetto ICE D.R. 975 del 26/11/2209

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


EXPERIMENTAL METHOD

Level trasducers

Load cells

Rectangular flume (dim. 4 x 0.4 x 0.7 m, inclined 30°)

Barrier (rigid or flexible)

35 fps cameras

0.400 m^3

Bottom dumping hopper


EXPERIMENTAL METHOD

Flows of water saturated sandProperties of the mixture

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


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)

3. Adimensional impact force

2. Froude number of the frontg

fgh

vFr

2

max

2

1~

gmhg

FF


DATA ANALYSES AND FIRST RESULTS

and comparing the obtained value of the adimensional impact force with the following formulations:

1. Momentum balance: (vertical jet-like wave) AvF m2

2. Hungr (1984): AvF m25.1

3. Campania Region (After Sarno, 1998), Japan AghAvF fmm 2

12

4. Armanini & Scotton (1993): AhF max5.4 Adimensional Formulation

1.

2.

3.

4. 9~ F

22~

fFrF

23~

fFrF 221

~fFrF


0 1 2 3 4 5 6 7 8 9 100

100

200

300

400

500

600

f(x) = 1.62223008016411 x^2.19639549679622R² = 0.811027296041342

Measured Adimensional ForcePower tdlineArmanini & Scotton (1993)

Froude Number

Adi

men

sion

al F

orce

Rigid barrier perpendicular to the channel


Rigid barrier in vertical position

0 1 2 3 4 5 6 7 8 9 100

100

200

300

400

500

600f(x) = NaN x^NaNR² = NaN

Measured Adimensional Force

Power tdline

Armanini & Scotton (1993)

Froude Number

Adi

men

sion

al F

orce


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)


Rigid filter barrier in vertical position

0 1 2 3 4 5 6 7 80

100

200

300

400

500

600

Measured Adimensional ForceArmanini & Scotton (1993)

Froude Number

Adi

men

sion

al F

orce


Net barrier vertical position

0 1 2 3 4 5 6 7 80

100

200

300

400

500

600

Measured adimensional forceArmanini & Scotton (1993)

Froude Number

Adi

men

sion

al F

orce


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.

More tests will be conducted, changing the characteristics of the mixtureand trying to evaluate the additional load due to

collisional force of a single boulder.

Filter and flexible barrier do not cause this phenomenon.

Real scale tests will be performed on a flexible net.


Thank you for your attention!

Contacts:

[email protected]

[email protected]

Documents

“Debris Flow Risk mitigation by the means of rigid and flexible barriers. Experimental tests and impact analysis” Anna Maria Ferrero, Luigi Canelli Università