Soil Mechanics I 1 Basic characteristics for soils. Introduction Description State Classification

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1 Soil Mechanics I 1 Basic characteristics for soils Introduction Description State Classification 1

2 Introduction GEOTECHNICAL STRUCTURES [1] 2

3 Introduction Geotechnical (Engineering Geology) Site Investigation Input data for design (geotechnical, structural) Engineering Geology - maps, cross sections, rocks, soils, mineralogy, origin... Mechanical properties Strength Compressibility Permeability Technology compaction... Ground Water 3

4 Introduction GEOMECHANICS Mechanics of Rocks Mechanics of Soils Mechanics of Snow and Ice + Mechanics of Powders = MECHANICS OF PARTICULATE MATERIALS 4

5 Introduction PARTICULATE MATERIALS Influence of water on mechanical behaviour 5

6 Introduction Role of pore volume, pore liquid The pore liquid water exhibits the primary role in the soil (particulate materials) mechanical behaviour principle of effective pressure σ' = σ - u σ' controls the mechanical behaviour of soils (strength, deformation) 6

7 Introduction Rock bolts [3] 7

8 Introduction Rock bolts [3] 8

9 Introduction Rock bolts [3] 9

10 Introduction DILATANCY A further energy necessary for shearing dense particulate materials (below a limiting porosity) (Casagrande, 1936) 10

11 Introduction STRUCTURE, SENSITIVITY Leda Clay (Can) [2] 11

12 Introduction SUBSIDENCE Mexico Basin lowering of GWL (Legget and Karrow, 1982, Geology in civil engineering, McGraw Hill) 12

13 Introduction Influence of water pore pressures [1] 13

14 Introduction HISTORY of SM 1775 Coulomb (France) friction in soils - fortifications ca 1911 Atterberg (Sweden) clay plasticity 1925 Terzaghi (Austria, USA) - his book Erdbaumechanik... Theoretical soil mechanics (1943) = foundation of the new discipline; principle of effective stress (±1936); one-dimensional consolidation... Casagrande, Hvorslev (USA) strength, dilatancy, critical void ratio, plasticity, soil classification... Roscoe, Schofield, Wroth (UK Cambridge) the first theory combining deformations and strength based critical state soil mechanics Skempton (UK) colloid activity of clays, residual strength Fellenius, Petterson, Bishop, Janbu -...slope stability 's to 1960's from 1970 FEM, BEM... DEM... in geomechanics 14

15 Soil Description GRAIN SIZE DISTRIBUTION (= description, not state) sieving and/or sedimentation grading curve [2] 15

16 POPIS ZEMIN Sieving [4] 16

17 Soil Description Sedimentation using hydrometer Stokes' law v=f(d2;density, viscosity) [4] 17

18 POPIS ZEMIN Combination of sieving and sedimentation [4] 18

19 Soil Description Quantification of the grading curves: Effective diameter: Def = D10 to D20 Uniformity coefficient: CU = D60 / D10 CU< ca 5 uniform soil = poorly graded CU>15 non-uniform soil (well graded) Coefficient of curvature: CC = (D30)2 / (D60 D10) CC = 1 to 3 (and CU> 4 to 6) well graded CC = <1 or >3 gap-graded 19

20 Soil Description EN Particle size Fractions 20

21 Soil Description - Classification Composite soil: Principal fractions Secondary fractions sagr = sandy gravel grcl = gravelly clay Interlayered soil e.g.: gravelly clay interbedded with sand: grclsa 21

22 Soil Description State WATER CONTENT STATE w = Mw / Md = Mw / Ms Volumetric water content θ = Vw / Vt ( = S n) 22

23 Soil Description CONSISTENCY LIMITS ( Atterberg limits ) Liquid limit wl (the water content at which the soil changes from liquid to solid material with plastic behaviour) Plastic limit wp (with further decrease of the water content the soil stops being plastic) Shrinkage limit ws Determination on a paste, D < 0.4 mm Plasticity index IP= wl-wp DESCRIPTION (= constants for a given soil!) 23

24 Soil Description Liquid limit wl [4] Looking for water content at which an arbitrary penetration is reached (10mm with 60º/60g cone (20mm with 30º/80g)) 'foundation' failure undrained strength of about 2-3 kpa 24

25 Soil Description Liquid limit wl [2] Casagrande method Looking for the water content at which the groove closes at 10 mm (slope failure undrained strength of about 2-3 kpa) 25

26 Soil Description Casagrande apparatus [2] 26

27 Soil Description Plastic limit wp [2] Looking for the water content at which the soil crumbles as shown undrained strength of about kpa 27

28 Soil Description - Classification PLASTICITY Casagrande plasticity chart PLASTICITY (L, I, H...) determined by wl only 28

29 Soil Description [2] 29

30 Soil Description ACTIVITY A (of clay minerals) A (= IA) = IP / (% of clay fraction by mass) (Skempton, 1953) 30

31 State properties CONSISTENCY (STATE) - fine-grained soils Consistency Index IC = (wl-w) / (wl-wp) Liquidity Index IL=(w-wP) / (wl-wp) Consistency: liquid IC<0 soft, firm (plastic) IC = 0 to 1 stiff IC >1 EN very soft soft firm stiff very stiff IC<0,25 IC = 0,25 to 0,50 IC = 0,50 až 0,75 IC = 0,75 až 1,0 IC > 1,0 31

32 State properties Amount of pores / voids POROSITY n = Vp / Vt VOID RATIO e = Vp / Vs... phase diagram 32

33 State properties DENSITY (UNIT MASS) Density of solid particles - Specific density (description not state) ρs= Ms / Vs = Md / Vs Density at natural water content (bulk density) ρ = Mt / Vt = (Mw +Md) / Vt Saturated density ρsat= Mt / Vt = (Mw +Md) / Vt Dried density ρd= Md / Vt 33

34 State properties UNIT WEIGHT γ = ρg...unit weight under water table: Archimédes law γ' = γsat γw 34

35 State properties Determination of densities - determination of volume density of solid particles density bottle 35

36 State properties Determination of densities - determination of volume Other densities ρ, ρsat, ρd - undisturbed sample cylinder/cube measuring the dimensions - undisturbed sample irregular shape weighing under water / expelled water 36

37 State properties...determination of densities - determination of volume - if impossible to take undisturbed sample (sands...) measuring of the volume of excavation (and weighing the excavated soil) 37

38 State properties Using the phase diagram for useful expressions for example e = n / (1 - n) ρd = ρs / (1 + e) determination of e from the dry density: e = (ρs ρd) / ρd ρd = ρ / (1 + w);...etc... 38

39 State properties Degree of saturation S ( Sr) S = Vw / Vp Determination from e and w 39

40 State properties RELATIVE DENSITY ID=(emax- e) / (emax- emin) loose medium dense ID= 0 to 0,33 ID = 0,33 to 0,67 ID = 0,67 to 1 very loose loose medium dense very dense ID= 0 to 0,15 ID= 0,15 to 0,35 ID= 0,35 to 0,65 ID= 0,65 to 0,85 ID = 0,85 to 1,0 40

41 Role of Fines and of Def Clayey sand (25% C a 75% S) of e = 0,5. What is the role of clay fraction in the mechanical behaviour of the soil? Consider removing of clay fraction: e = 1,0 The loosest sand with its spherical particles in contact: e<1 Sand grains (spheres) at e = 1 cannot be in contact At 25% of C and 75% of S spherical grains 'float' in the clay 'matrix' Clay may be expected to control the behaviour of the above soil having just 25% of clay fraction 41

42 Role of Fines and of Def Change in hydraulic conductivity (permeability) with the amount of fines (in a mixture of ash and sludge) 42

43 Role of Fines and of Def Change in strength with the amount of fines (in a crushed rock) (Mašín, 2000) 43

44 Examples of Use of Grading Curve (± Description) Estimation of emin and emax of a snad from Cu and shape of grains (Youd, 1973 in Mitchell and Soga, 2005) 44

45 Examples of Use of Grading Curve (± Description) Dependence of emin a emax on amount of silt fraction in a sand (Polito and Martin, 2001 in Mitchell and Soga, 2005) 45

46 Examples of Use of Grading Curve (± Description) Estimation of hydraulic conductivity of a sand Hazen: k [ms-1] = 0,01D102 [mm]...fine and medium sand: k = [A / (Cu+B) + C] D102, where A, B a C depend on density Estimation of hydraulic conductivity of fine-grained soil k = f (e, wp, IP) k = f (e, CF%, IA) (full correlations in Soos and Boháč (2002), Geotechnical Engineering Handbook, Ernst & Sohn) 46

47 Examples of Use of Grading Curve (± Description) Use of soil in filters (Cedergren, 1988) D15(of filter) / D85 (of soil) < 4 to 5 < D15(of filter) / D15 (of soil) 47

48 Examples of Use of Grading Curve (± Description) Use of soil in fills Dams for the impervious core the soil must be from the zone 1 or 2; for the stabilisation part from zone 3 or 4 48

49 Examples of Use of Grading Curve (± Description) Use in estimating frost heave frost susceptibility (Beskow, 1935 in [2]) [2] 49

50 Soil POJMENOVÁNÍ Classification Classification according to EN Grading only [5] 50

51 Soil Classification USCS classification grading + plasticity chart The Czech modification: + 51

52 Literature for the course Soil Mechanics II Atkinson, J.H. (2007) The mechanics of soils and foundations. 2nd ed. Taylor & Francis. Further reading: Wood, D.M. (1990) Soil behaviour and critical state soil mechanics. Cambridge Univ.Press. Mitchell, J.K. and Soga, K (2005) Fundamentals of soil behaviour. J Wiley. Atkinson, J.H: and Bransby, P.L. (1978) The mechanics of soils. McGraw-Hill, ISBN Bolton, M. (1979) A guide to soil mechanics. Macmillan Press, ISBN Craig, R.F. (2004) Soil mechanics. Spon Press. Holtz, R.D. and Kovacs, E.D. (1981) An introduction to geotechnical engineering, Prentice-Hall, ISBN Feda, J. (1982) Mechanics of particulate materials, Academia-Elsevier.) 52

53 References (used figures) [1] Atkinson, J.H. (2007) The mechanics of soils and foundations. 2nd ed. Taylor & Francis. [2] Holtz, R.D. and Kovacs, E.D. (1981) An introduction to geotechnical engineering, Prentice-Hall, ISBN [3] Hoek, E. (2007) Practical rock engineering (2007 edition). (downloaded 2008/02). [4] TS/ISO [5] EN ISO

Soil Mechanics I 3 Water in Soils. 1. Capillarity, swelling 2. Seepage 3. Measurement of hydraulic conductivity 4. Effective stress in the ground

Soil Mechanics I 3 Water in Soils 1. Capillarity, swelling 2. Seepage 3. Measurement of hydraulic conductivity 4. Effective stress in the ground 1 Influence of Water - Basics WATER IN SOIL - affects soil