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Cedex Madrid - Politecnico di Milano
Analysing the Chemo-mechanical coupling in BVP: Analysing the Chemo-mechanical coupling in BVP:experimental set-upexperimental set-up
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WeatheringWeathering of a cemented silica sand: an artificial soft rock of a cemented silica sand: an artificial soft rock
1) SILICA SAND1) SILICA SAND
Part 1: Experimental study Part 1: Experimental study
After immersion in acid solution: After immersion in acid solution: • Progressive dissolution of calcareous intergranular bondsProgressive dissolution of calcareous intergranular bonds
CaCO3 + 2 H3O+ <=> Ca2+ + 3H2O + CO2 (gas)
Calcite Acid Calcium Water Carbon Dioxide
2)LIME2)LIME
3) WATER3) WATER
•COMPONENTSCOMPONENTS •ARTIFICIAL SOFT ROCKARTIFICIAL SOFT ROCK
INTACT (cemented sand)INTACT (cemented sand) COMPLETELY WEATHERED (unbonded sand)COMPLETELY WEATHERED (unbonded sand)
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Experimental measures on carbonate dissolution reactionExperimental measures on carbonate dissolution reaction CaCO3 + 2 H3O+ <=> Ca2+ + 3H2O + CO2 (gas)
Calcite Acid Calcium Water Carbon Dioxide
We will use artificial cemented sand: the initial amount of CaCO3 is known if we assume a complete lime hydration.
Anyway we can measure it in the chemical lab.
It means to measure the pH value. We will use electronic pH_meter to get precise and continuous measures
We will use a electronic ion chromatograph to get precise and continuous measures
•We also know the total amount of ion H+ to dissolve all the initial amount of CaCO3.
•Ning et al (2003)
•The kinetic of this reaction has been widely studied by chemical researchers
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COLUMN TEST: monodimensional chemo-mechanical tests with acid transportCOLUMN TEST: monodimensional chemo-mechanical tests with acid transport
•Using the WTD, but with an HIGHER specimen
Specimen
Axial load
Strain gaugesAcid flow
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COLUMN TEST: monodimensional chemo-mechanical tests with acid transportCOLUMN TEST: monodimensional chemo-mechanical tests with acid transport
•Using the WTD, but with a HIGHER specimen and measuring pH and Ca2+ at different levels
hh
AAcciidd ffllooww
a = const.
ACID FLOW
Axial stress
Axial strain
Radial stress
• pH Output
• [Ca2+] output
water flow
• pH and [Ca2+] measures at different levels
• pH Input
Mechanical:
-Axial stress
-Radial stress
-Axial strain
-Radial strain
Fluid :
-Fluid Velocity
-Pore pressure
Chemical:
-Source input boundary
-Chemical species H+ Ca2+
•Dimension : diam. 50mm, heigh 100mm
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Experimental BVP-Weathering induced subsidence of a shallow foundation Experimental BVP-Weathering induced subsidence of a shallow foundation
Automatic load system with both load and displacement control
Available Experimental apparatus
Box test (plane strain)
(890 x 440 x 200 mm)
Photogrammetric acquisition of subsoil displacement field
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Experimental BVP-Weathering induced subsidence of a shallow foundation Experimental BVP-Weathering induced subsidence of a shallow foundation
Automatic load system with both load and displacement control
Available Experimental apparatus
Box test (plane strain)
(890 x 440 x 200 mm)
Photogrammetric acquisition of subsoil displacement field
Ready for test
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Apparatus scheme
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0
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0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35
Spostamento verticale (mm)
Car
ico
ver
tica
le (
Kg
)
Photogrammetric acquisition of subsoil displacement field
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• Digital calibrated photocamera • Reference markers
• Image analisis
Photogrammetric acquisition of subsoil displacement field
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CORRELAZIONE A MINIMI QUADRATI
si ricerca la massima somiglianza tra i toni di grigio dei pixel della FINESTRA di RIFERIMENTO, f(i,j)
min),(),( 2 i j
jigjif
la convergenza al minimo è ottenuta • iterativamente partendo da un’approssimazione della posizione iniziale pari a 5 pixel
MODELLO GEOMETRICO:• trasformazione affine
MODELLO RADIOMETRICO:• correzione preliminare col FILTRO DI WALLIS
e
quelli della FINESTRA MOBILE, g(i,j) :
• variando, attraverso un ricampionamento, FORMA, POSIZIONE, TONI DI GRIGIO della finestra mobile.
posizioneiniziale
posizionefinale
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SITUAZIONE INIZIALE
SITUAZIONE FINALE
FASE OPERATIVA
sulla prima immagine si selezionano, etichettano, misurano
i punti d’interesse
su immagini seguenti si predicono le coordinate approssimate
considerando gli spostamenti precedentemente valutati
prova n°2:99/102 sferette su 40 immagini
prova n°1:175/190 sferette su 77 immagini
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Test 2 results Gid postprocessor
EVOLUZIONE DEGLI SPOSTAMENTI DALL’ISTANTE INIZIALE
MESH D’ORIGINE
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D'C'
B'
A'
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
6.5
7.0
7.5
8.0
0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300
tempo (secondi)
Sp
ost
am
en
to V
ert
ica
le (
mm
)
Sfera 11
Sfera 28
Sfera 62
Sfera 79
Sfera 45
Comparison with settlement-load curve
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Experimental BVP#1-Weathering induced subsidence of a shallow foundation Experimental BVP#1-Weathering induced subsidence of a shallow foundation
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Experimental BVP#2-Pumping oil -injecting water Experimental BVP#2-Pumping oil -injecting water
AA BB
Silica sand : n= 0.3-0.4Silica sand : n= 0.3-0.4
Water conductivity k=1*10Water conductivity k=1*10-3-3 m/s m/s
Imposing water pressure in injection camera A and im the pumping camera B:Imposing water pressure in injection camera A and im the pumping camera B:
Rwsolution of 1 kPa , range from 0-1000 kPaRwsolution of 1 kPa , range from 0-1000 kPa
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