Cedex Madrid - Politecnico di Milano

Analysing the Chemo-mechanical coupling in BVP: Analysing the Chemo-mechanical coupling in BVP:experimental set-upexperimental set-up

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)

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

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

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

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

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

Apparatus scheme

0

10

20

30

40

50

60

70

80

90

100

110

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

• Digital calibrated photocamera • Reference markers

• Image analisis

Photogrammetric acquisition of subsoil displacement field

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

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

Test 2 results Gid postprocessor

EVOLUZIONE DEGLI SPOSTAMENTI DALL’ISTANTE INIZIALE

MESH D’ORIGINE

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

Experimental BVP#1-Weathering induced subsidence of a shallow foundation Experimental BVP#1-Weathering induced subsidence of a shallow foundation

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