Integrated Ground Behavior

Size: px

Start display at page:

Download "Integrated Ground Behavior"

Lewis Briggs
5 years ago
Views:

1 Integrated Ground Behavior Part A: Particle-level Phenomena & Macroscale Behavior (J. Carlos Santamarina) Georgia Institute of Technology

2 fluid particles microorganisms mineral size shape surface charge double layers capillarity forces specific surface relative size sphericity roundness smoothness soil fine-grained soil fabric coarse-grained soil packing platy particles conduction diffusion energy coupling stiffness threshold strain strength (scales) rheology diagenesis

3 fluid particles microorganisms mineral size shape surface charge double layers capillarity forces specific surface relative size sphericity roundness smoothness soil fine-grained soil fabric coarse-grained soil packing platy particles conduction diffusion energy coupling stiffness threshold strain strength (scales) rheology diagenesis

4 Water Ionic concentration acid ph= 7 basic H + OH - NaCl HCl NaOH

5 Minerals montmorillonite OH - O = kaolin Al octa Si tetra Si tetra Al octa Si tetra calcite MDL /

6 Diffuse double layer Stern layer Gouy diffuse layer bulk electrolyte ψ St mineral surface ζ ψ St / e shear plane ψ e -x O = OH - ~ t ddl x ph ionic concentration & valence

7 Mixed fluid phase Interacting menisci: θ non-constant

8 fluid particles microorganisms mineral size shape surface charge double layers capillarity forces specific surface relative size sphericity roundness smoothness soil fine-grained soil fabric coarse-grained soil packing platy particles conduction diffusion energy coupling stiffness threshold strain strength (scales) rheology diagenesis

9 Particle Forces Skeletal 2 N = σ'd #200 Weight Buoyant W = ( πg U = ( π γ s w γ w / 6) d / 6) d 3 3 skeletal & weight (Terzaghi) Hydrodyn. F drag = 3πμ vd fines detach coarse v Capillary F cap = πt s d capillary El. attraction Ah Att = 2 24t d electrical El. repulsion Re p = 24 co e 8 t c o d Cementation T = πσtent d μm diameter d mm

10 Size and Surface - Surface Phenomena Specific Surface [m 2 /g] 10 4 m 2 /g 10 2 m 2 /g 1m 2 /g 10-2 m 2 /g S s = max for any mineral montmorillonite ~ 6 L ρ min illite kaolinite Si flour 1μm Ottawa m 2 /g nm μm mm Particle Size L min

11 Size and Surface - Surface Phenomena Cum. Distribution Surface Weight Density Grain size

12 Fines migration and bridge formation D/d=2.4 MICA GLASS BEADS SAND clog clog pass pass clog pass D/d= Pore size / d fines

13 Particle Shape sphericity vs. ellipticity..platiness roundness vs. angularity smoothness vs. roughness 100μm 1 μm 100μm 1 μm Ottawa PCC Nevada formineferan

14 Particle Shape chemically controlled 50 μm mechanically controlled 1μ 100μm kaolinite Margaret River

15 fluid particles microorganisms mineral size shape surface charge double layers capillarity forces specific surface relative size sphericity roundness smoothness soil fine-grained soil fabric coarse-grained soil packing platy particles conduction diffusion energy coupling stiffness threshold strain strength (scales) rheology diagenesis

16 Fabric map kaolinite ph Edge IEP, ph 7.2 Silica dissolution - coagulation (ph>8) Face or Particle IEP ph 4 No global repulsion - vdw deflocculateddispersed deflocculateddispersed particle dissolution - liberation of Al 3+ - coagulation (ph<2) c o = mol/l Stern potential and R DL decrease van der Waals attraction prevails log(c o )

17 Clay minerals Differences 1:1 OH - O 2- O 2- OH - 2:1 O 2- - O 2- O 2- OH - different faces edge contribution ζ / particle thickness different from edge charge change hiding edge DL

18 Coarse particles: relative size random packing: D/d=1.37 porosity, n D/d=2 D/d= (Guyon et al., 1987) D/d= % volume fraction of small particles and

Relative size and shape 1.4 sphericity 0.9 0.7 0.5 0.

9 i roundness r = r max N minimum e min maximum e max 1.2 1.0 0.

19 Relative size and shape 1.4 sphericity (Krumbein and Sloss, 1963) i roundness r = r max N minimum e min maximum e max coefficient of uniformity, C u (Youd, 1973; see also Maeda, 2001)

20 Platy particles: bridging 1.2 sand + mica L m /d s = 3 void ratio L m /d s = 2 L m /d s = % mica

21 fluid particles microorganisms mineral size shape surface charge double layers capillarity forces specific surface relative size sphericity roundness smoothness soil fine-grained soil fabric coarse-grained soil packing platy particles conduction diffusion energy coupling stiffness threshold strain strength (scales) rheology diagenesis

22 Small-strain stiffness: Contact-controlled coarse grains V S = α σ' kp a 1 β= 6 (Frocht, 1941) fine grains V S = α σ' kp a β< 3 4 (N. Skipper UCL 2002)

23 Stiffness-Stress: contact behavior & fabric changes Very soft clays V S = α σ' x + σ' 2 kp a y β β exponent Sands β= α/700 OC clays Cemented soils α-factor [m/s]

24 Stiffness: platy particles Vs [m/s] % sand 1% mica 5% mica 10% mica 100% mica 50 0 L m /d s = load [kpa]

25 Particle shape effects V S σ' x + σ' = α 2 kpa β= α/700 y β β 0.5 platy particles β 0.5 roundness + sphericity (R+S)/2 < (R+S)/2 > mica sand α factor [m/s] α factor [m/s]

26 Drying Unsaturated media 1200 Shear wave velocity [m/s] glass beads + kaolinite Degree of saturation S

27 Stress change and cementation Load (no unloading) V s [m/s] 700 Unload and reload V s [m/s] 700 β = β~ β = β= β= V s [m/s] cementation Uncemented V s [m/s] β= 0.18 Uncemented Confining Pressure [kpa] Confining Pressure [kpa]

28 Strain regimes Small Strain Large Strain Deformation at contacts fabric changes Stiffness maximum decreases Losses very low large - frictional Volume Change minimal potentially large Diagenetic effects potentially high small in drained shear Fabric constant changes towards CS

29 Threshold strains - Ranges w =10% 10-1 w =1% Threshold Strain [ ] γ dt ξ = 1.2 d 2t δ = m ξ δ = 10 8 m high σ o low σ o γ dt ' 1.3 σ = Gg 2/ Particle Size [m]

30 fluid particles microorganisms mineral size shape surface charge double layers capillarity forces specific surface relative size sphericity roundness smoothness soil fine-grained soil fabric coarse-grained soil packing platy particles conduction diffusion energy coupling stiffness threshold strain strength (scales) rheology diagenesis

31 Stress-dependent strength and ε vol Chain buckling: coordination Rotational frustration: coordination Deviatoric Stress [kpa] Vertical strain [%]

32 Effect of roundness on Φ cv 50 CS friction angle cv φ cv = R Roundness R

33 Evolution of internal micro-scale 3D Contact normals N(θ) Isotropic confine. At peak dev. load AC (b=0) AE (b=1) T(θ) (magnified x5) Chantawarangul, 1993

34 Constant angle of repose? φ int φ ext 60 φ int =1.5 φ ext Internal angle φ int =φ ext External angle Narsilio, Dodds, Fugle, Trott, Kim, Yun

35 Anisotropy in φ - Clays 60 φ E =1.5 φ C φ extension φ compression φ E =φ C Mayne & Holtz 1985

36 Undrained strength anisotropy Controlled by the generation of pore pressure chain buckling and skeletal stiffness spatial variability of e cum. % smaller than 100% 0% increasing confinement or shear pore size (in log scale)

37 Undrained strength anisotropy Controlled by the generation of pore pressure chain buckling and skeletal stiffness spatial variability of e threshold strain 1.0 Su(AE) / Su(AC) Clays PI Mayne and Holtz 1985

38 Undrained strength anisotropy Controlled by the generation of pore pressure chain buckling and skeletal stiffness spatial variability of e threshold strain fabric anisotropy AC Fraser River Sand AC: b=0 α=0 SS: b>0 α>0 AE: b=1 α=90 SS AE Vaid and Sivathayalan 1996

35 Scales temporal spatial q T (MPa) t L load 2 / c v drained or undrained 0 5 0 10 20 30 40 f

39 35 Scales temporal spatial q T (MPa) t L load 2 / c v drained or undrained f f res quasi-static or dynamic Depth (m) L 2 L / ki / c v seepage or consolidation 25 30

fluid particles microorganisms mineral size shape surface charge double layers capillarity forces specific surface relative size sphericity roundness smoothness soil

40 fluid particles microorganisms mineral size shape surface charge double layers capillarity forces specific surface relative size sphericity roundness smoothness soil fine-grained soil fabric coarse-grained soil packing platy particles conduction diffusion energy coupling stiffness threshold strain strength (scales) rheology diagenesis

41 Gravel: < 5% fines C u >4, 1 C c 3 relative size else GW GP COARSE > 50% retained sieve #4 > 12% fines Below 'A' line Above 'A' line GM GC > 50% retained sieve # μm FINE < 50% retained sieve #200 Sand: < 50% retained sieve #4 LL<50 LL>50 plasticity index < 5% fines filled porosity > 12% fines 0 mineral, S s pore fluid CL CL-ML ML CL OL or ML C u >6, 1 C c 3 CH else Below 'A' line Above 'A' line OH or MH A line liquid limit SW SP SM SC ML CL OL MH CH OH

42 pore fluid (explicitly) Gravel: < 5% fines C u >4, 1 C c 3 else GW GP COARSE degree > 50% of retained saturation > 12% fines sieve #4 particle shape - coarse Below 'A' line Above 'A' line > 50% C u >6, 1 C c 3 retained < 5% fines else sieve #200 Sand: specific surface - fines (explicitly) < 50% retained > 12% fines extent sieve of diagenesis #4 60 inherent anisotropy 50 FINE LL<50 40 plasticity index spatial variability < 50% 20 CL retained bio-activity and bio-viability 10 CL CL-ML OL or sieve #200 LL>50 ML ML 0 30 Below 'A' line Above 'A' line CH OH or MH A line liquid limit GM GC SW SP SM SC ML CL OL MH CH OH

Discontinuities in Soils

Institute for Geotechnical Engineering ETH Zurich March 17 2011 Discontinuities in Soils J. Carlos Santamarina Georgia Institute of Technology A. Lizcano UniAndes J. Cartwright Cardiff U. H. Shin Hongik