Physical based models of Landslides' triggering
-
Upload
cafe-geoframe -
Category
Education
-
view
1.318 -
download
1
description
Transcript of Physical based models of Landslides' triggering
Riccardo Rigon, Giuseppe Formetta, Giovanna Capparelli, Fabio Ciervo, Mariolina Papa
Process -based models of landslide triggering (especially the hydrological parts)
Giornata di Studio su: “La modellazione dell’innesco dei movimenti franosi - Rende 7 Novembre 2013
We feel clearly that we
are only now beginning to acquire reliable
material for welding together the sum total of all
that is known into a whole; but, on the other
hand, it has become next to impossible for a
single mind fully to command more than a small
specialized portion of it.
!E. Schroedinger (What is life ?)
!3
What’s the physics of landslides ?
Hillslope Hydrology
Introduction
Rigon et al.
Hillslope stability
+
!4
Hillslope Hydrology
bricks
Introduction
Darcy hypothesis
Mass conservation
Soil water retention curves (SWRC)
Fluxes Hypothesis
Eventually assume a theory that relates SWRC to fluxes
Rigon et al.
!5
Darcy’s hypothesis
Hillslope hydrology
Rigon et al.
This is the REV Representative Elementary Volume
!6
Richards’ equation core
is that what it is true is this
Mass conservation (no nuclear reactions) ! but actually true if the continuum (a.k.a. Darcy) hypothesis is valid
Hillslope hydrology
Rigon et al.
!7
Assume a parametric form of soil water retention curves
Se :=�w � �r
⇥s � �r
Parametric van Genuchten (1981)
C(⇥) :=⇤�w()⇤⇥
Se = [1 + (��⇥)m)]�n
But other forms are possible ...
Hillslope hydrology
Rigon et al.
!8
Flux hypothesis
Darcy-Buckingham Law
Volumetric flow through the surface of the infinitesimal volume
Hydraulic conductivity times gradient of the hydraulic head
Bu
ckin
gh
am, 1
90
7, R
ich
ard
s, 1
93
1
~Jv = K(✓w)~r h
Hillslope hydrology
Rigon et al.
!9
A theory for getting hydraulic conductivity from soil water retention curves
K(�w) = Ks
⇧Se
⇤�1� (1� Se)1/m
⇥m⌅2
But other forms are possible also here...
Hillslope hydrology
Rigon et al.
!10
Now you can simplify it
Hillslope hydrology
http://abouthydrology.blogspot.it/2013/06/ezio-todini-70th-symposium-my-talk.html
Rigon et al.
!11
Simplifications with more details
http://abouthydrology.blogspot.it/2013/07/hillslope-hydrology-from-point-of-view.html
An outcome of this project
Rigon et al.
!12!12
Soil depth
Soil
rocks
Where does water flow ?
The medium is the message
Rigon et al.
!13
Because is usually believed that it is the perched water
table that can form at soil
discontinuity that causes shallow landslides
Soil depth is particularly important for landslides
The medium is the message
Rigon et al.
Perched water table
Water table
http://abouthydrology.blogspot.it/2012/09/soil-depth-estimation.html
!14
Hillslope stability
bricks
Stresses (and strains)
Effective stresses
Soil stresses characteristics curves (SSCC)
Material strength (Coulomb Hypotesis)
Factor of safety
Rigon et al.
Geomechanics
!15
I do not enter into
the geotechnical
details
Rigon et al.
http://www.camilab.unical.it/summer_school/index.html
Geomechanics
!16
Commercial a good book save a lot of searching
N. Lu, J. Godt,Hillslope Hydrology and Stability, Cambridge University Press, 2012
Rigon et al.
Geomechanics
!17
Advancing Knowledge Promoting Learning�
6.#Effec(ve#Stress#in#Soil�
! Suction stress is the effective stress (skeleton stress) with zero total stress.
! Suction stress is the work done by the inter-particle stress or internal stress due to water.
! What are the components of the inter-particle stress σs?
What is Suction Stress?
11
s
s
s s
Dry: no stress (a)
Wet: internal suction stress (b)
Dry: equivalent suction stress (c)
dε1 dε1
dε 2
dε 2
! s = !!C = !! cap !! pc ! S ua !uw( )
Rigon et al.
However, let me say something
Dry: no stress Dry: equivalent suction stressWet: internal
suction causes , and correspondent
strain
Geomechanics L
u a
nd
God
t, 2
01
2
!18
Ning Lu
Geomechanics
!19
Lu
an
d G
od
t, 2
01
2
Effective stress at REV is the composition of several
forces acting at micro scale
Advancing Knowledge Promoting Learning�
6.#Effec(ve#Stress#in#Soil�
! To define a stress that accounts for soil saturation and is “effective” in describing strength and deformation at Representative Elementary Volume (REV).
Stresses at sub-pore scale " forces at pore scale " stress at soil REV scale
Rationale for Suction Stress Characteristic Curve
10
Fc
uw
Fcap
ua
Fpc
A
Aa2
Aa3
Aw1
Aw2
Aw3
Ac1
Ac2
Ac3
Area of REV Cross-Section
Aa1
Aa4
Fc
uw
Fcap
ua
Fpc
A
Aa2
Aa3
Aw1
Aw2
Aw3
Ac1
Ac2
Ac3
Area of REV Cross-Section
Aa1
Aa4
w uwSa ua 1 S( )cap = fcap (S)pc = fpc (S)
' = ua( ) + S ua uw( ) + cap + pc
' = ua( ) s
s = S ua uw( ) cap pc
c = - s
Soil-Water-Air REVContinuum Media
cap a
c = -
wpc
c = -Soil-Water-Air REVContinuum Media
cap a
c = -
wpc
c = -Soil-Water-Air REVContinuum Media
cap a
c = -
wpc
Ft
Suction stress�
Rigon et al.
Geomechanics and vadose zone hydrology
!20
Effective suction stress is then:
Effective stress
Lu
an
d G
od
t, 2
01
2
Rigon et al.
Stress in material
air pressure
Suction stress
Geomechanics and vadose zone hydrology
!21
Effective suction stress is then:
capillarity
interparticle stresses
relative water content
water pressure
Rigon et al.
Geomechanics and vadose zone hydrology
!22
Soil Suction Characteristic Curves
SSCC
As a result of Lu et al. 2010 work, suction stress can be expressed as a
function of the SWRC:
Se :=�w � �r
⇥s � �r
Parametric van Genuchten (1981) Se = [1 + (��⇥)m)]�n
from slide 7
Geomechanics and vadose zone hydrology
Rigon et al.
!23
Therefore
Rigon et al.
Geomechanics and vadose zone hydrology
The determination of the SWRC is of fundamental
importance, and the key to predict both soils
suction and stress evolution in hillslopes
What about hillslope
failure ?
!24
Geomechanics and vadose zone hydrology
FoS
Factor of Safety
Rigon et al.
Both Material Strength and Design Loads, in
the hillslope game are function of the stresses
Details in Lu and Godt, 2012 and references therein
!25
To sum up
We have a sound and comprehensive theory
!
GEOtop and its brothers and sisters
!27
So what ? We have the theory (and the equations)!
However we have to
implement it in sound numerical code
to identify the parameters (and there are quite a few)
treat the input and the output data
Rigon et al.
!28
GEOtop
!• it models: !- subsurface saturated and unsaturated flows !
- surface runoff !
- turbulent fluxes across the soil-atmosphere interface.
Rig
on
et
al.,
20
06
, En
dri
zzi
et a
l., 2
01
3GEOtop as a tool of this project
Rigon et al.
!29
GEOtop
• 3D physically based finite-difference model !!
• spatially distributed
Rig
on
et
al.,
20
06
, En
dri
zzi
et a
l., 2
01
3GEOtop as a tool of this project
Rigon et al.
!30
Dav
id
et
al.,
20
13
Model integration with OMS
The Object Modeling System is a modular modeling framework that,
using an open source software approach, enables all members of the
scientific community to address collaboratively the many complex
issues associated with the design, development, and application of
distributed hydrological and environmental models.
Features
Components interoperability
Data interoperability
Language interoperability
GEOtop as a tool of this project
Rigon et al.
!31
In reality GEOtop is the most complex of a series
of models
and one scope is to compare many of them, and eventually use them for different purposes. In red those already implemented for the project.
Other tools
Rigon et al.
!32
GEOtop:
https://code.google.com/p/geotop/
CISLAM and SHALSTAB:
https://code.google.com/p/jgrasstools/
code at:
code at:
information at: http://abouthydrology.blogspot.it/search/label/GEOtop
information at:http://abouthydrology.blogspot.it/2012/09/my-past-research-on-shallow-landslide.html
Every is free … as “free of speech"
!33
Many landslides models with many physical approximations !• Does exist a minimum physical degree of simplification to
model a landslide? !
• Is it possible create a unique modeling framework where different models can be executed and compared? !!!!!!
Research but also practical questions
Rigon et al.
Questions
!34
Waiting for the data
… an application where we have some
TuostoloRigon et al.
It works!
!35
Measurement station
Some results
Rigon et al.
It works!
!36
Measurement station
• Suction [KPa] simulation at 0.35 m depth !
• Simulation period: 01-12-2007 to 01-05-2008
PBIAS=1.90 NSE=0.83
Rigon et al.
It works!
Tuostolo - Campania- Italy
!37
Tuostolo - Campania- Italy
• Soil moisture simulation at 0.35 m depth !
• Simulation period: 01-12-2007 to 01-05-2008 !• Time step: hourly
PBIAS=2.1 NSE=0.70
!38
Drake River - CO - USA
Trento 17 June 2011G. Formetta, Trento 24 June 2011G. Formetta,
C1
C3
Input data: • Radiation • Rainfall • Air Temperature • Relative Humidity !Output: • soil moisture at
different depths
!39
Simulation period: 01/09/2008-01/02/2009 !Simulation timestep: hourly
Drake River - CO - USA
!40
Simulation period: 01/09/2008-01/02/2009 !Simulation timestep: hourly
Drake River - CO - USA
Suction (mm)
30 cm depth
50 cm depth
!41
Simulation period: 01/09/2008-01/02/2009 !Simulation timestep: hourly
Drake River - CO - USA
Suction (mm)
30 cm depth
50 cm depth
!42
Simulation period: 01/09/2008-01/02/2009 !Simulation timestep: hourly
Drake River - CO - USA
Suction (mm)
30 cm depth
50 cm depth
!43
Safety factor
Drake River - CO - USA
!44
Comments
• GEOtop seems able to reproduce decently suction and water contents
• Therefore it can be reliably used for trying a forecasting of these quantities
• Certainly more analysis and data are required
It works!
Rigon et al.
The IWL3 Round Robin
!46
Thanks to Neaples Group: the IWL3 experiment
R. Greco1, L. Comegna1, E. Damiano1, A. Guida1,2, L. Olivares1, and L. Picarelli1
1Dipartimento di Ingegneria Civile Design Edilizia e Ambiente, Seconda Università di Napoli, via Roma 29, 81031 Aversa (CE), Italy 2Centro Euro-Mediterraneo sui Cambiamenti Climatici, via Maiorise, Capua (CE) 81043, Italy
GEOtop in the lab
Rigon et al.
!47
Tes t
nr.
Soi l Thickness (cm)
Slope Length (cm)
Initial porosity n0
Rainfal l intensity (mm/h)
Init ial mean suction (kPa)
Duration of test (min)
D3 10.0 100 0.75 55 17.5 36
D4 10.0 120 0.76 56 41.0 30
The inclination of the slope is 40°. !The test are carried out with constant and spatially homogeneous rainfall intensity.
Several devices (tensiometer, pore pressure transducer, TDR and laser
Rigon et al.
GEOtop in the lab
!48
. !!
first displacementfailure
first displacement
factor of safety here is 1.2
Suctions and pressures
-5 cm
-10 cm
Rigon et al.
Analysis of the data
!49
Water Content
Rigon et al.
Analysis of the data
!50
Water Content talks
Hydraulic conductivity was measured in the lab. The value given was around one order of magnitude less than the artificial rainfall
So we expect an Hortonian flux: saturation at the top and movement downward.
Which we do not have!
Rigon et al.
Analysis of the data
!51
So we expect an Hortonian flux: saturation at the top and movement downward.
red line is more ore less what we expect just after the beginning of irrigation in a Hortonian interpretation of infiltration
Rigon et al.
Analysis of the data
!52
What about the Darcy scale here ?
Rigon et al.
Questions
!53
Water Content talks
Is irrigation really stationary ? What happens after the 28th minute ? Lateral flow triggers ?
Rigon et al.
Analysis of the data
!54
Two hydraulic conductivities
One hypothesis we did is that, despite the homogeneity of the
preparation of the experiment, hydraulic conductivity (at
saturation) at the bottom is different from hydraulic conductivity at
the top of the mock-up.
Due to packing of particles ? Due to some unavoidable imperfection
in preparation ? Due to avoidable imperfection of the preparation ?
What else ?
Rigon et al.
Let’s go !
!55
Suction talks
Both suction and water content data were used to calibrate van Genuchten parameters. Also the hydraulic conductivity is among
Se :=�w � �r
⇥s � �r
Se = [1 + (��⇥)m)]�n
Also hydraulic conductivity at saturation is a calibration parameter
K(�w) = Ks
⇧Se
⇤�1� (1� Se)1/m
⇥m⌅2
Rigon et al.
Which parameters ?
!56
Calibrated Parameters
alfa n m0.052 1.805 0.445983
Ksat_layer superficiale (0-5cm) = 0.178 mm/s
Ksat_layer di fondo (5-10cm) = 0.117 mm/s
Rigon et al.
Which parameters ?
!57
Rigon et al.
Suctions
!58
Averaging does not get the right result
even if water contents are reproduced fairly well until the 21th minute
Rigon et al.
Water content
!59
Discussion
The friction angle of the material is 38 degrees. Therefore the stability
depends mainly on suction.
The FoS has been calculated into 2 different ways, by using the Fos
below that includes both the “classical” and “Lu’ Fos:
Rigon et al.
Analysis of the set up
!60
Stresses (FoS)
Rigon et al.
Stresswise
!61
Stresses (FoS)
Rigon et al.
Stresswise
!62
Comment
The way you calculate the FoS matters. While with the classical approach,
FoS remains consistently higher than 1 (close to 2), with Lu approach the
FoS comes close to 1.
In a sense, also this is not satisfactory, since we would like to have a
safety factor well below 1.
Do we neglected something ?
Rigon et al.
Stresswise
!63
Conclusion
We are close … but also far away …
The project allowed to set up an infrastructure that can be used to
investigate real cases, and to better tune experiments
On the present infrastructure can be incrementally built
“Real Time” physical modelling of these phenomena is feasible
Rigon et al.
What we gain
Thank you for your attention
G.U
lric
i, 2
00
0 ?
!64
La presentazione può essere scaricata da http://abouthydrology.blogspot.com
R. Rigon
Closing
!65
Do the physics simplify at hillslope scale ?
Which measures can we envision to make a verification of the theory ?
Can lab measures reproduce field ?
Questions
How we characterise spatial patterns (needed to check real cases) ?
The theory is sound … where it fails ?
What the relation between mass waste and erosion ?
How can we validate the overall process ?
What is the influence of these phenomena on landscape evolution ?
Rigon et al.
Closing
!66
What the role of plants’ roots in stability?
Questions
Rigon et al.
Closing