Laboratory testing of soils Soil Classifications

Transcription

1 Faculty of Civil Engineering Institute of Geotechnical Engineering Laboratory testing of soils Soil Classifications Recommended books & weblinks 1. Liu, C., Evett, J.B., Soils and Foundations (Sixth Edition). Prentice Hall. 2. Craig, R.F., Soil Mechanics. Chapman & Hall. 3. Simons, N., Menzies, B., Matthews, M., A short course in geotechnical site investigation. Thomas Telford. 4. Budhu, M., Soil Mechanics & Foundations. John Wiley & Sons. 5. Atkinson, J., An introduction to the mechanics of soil and foundation. McGraw-Hill. 6. Bowles, J.E., Foundation Analysis and Design. McGraw-Hill.

2 7. A. Verruijt: Soil Mechanics Soil Mechanics Laboratory, University of Illinois at Chicago 9. Earth manual, US Bureau of Reclamation USACE manuals (US Army Corps of Engineers) FHWA manuals (Federal Highway Administration) Descriptive (index) properties Nature of grains grain size, grain size distribution, surface, shape, mineralogy, specific gravity Current state water content, unit weight, porosity (void ratio), degree of saturation, stress Structure/Fabric layering, bedding, fissuring, joints, cementing (scale-dependent!) various classifications

3 Sand grains Loam

4 Clay Grains

5 Grain size distribution

6 Sieve sizes

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8 Grain size distribution Grading Coefficient of uniformity: C u = d 60 /d 10 Coefficient of curvature: C c = (d 30 ) 2 /(d 60 d 10 )

9 AASHTO classification (AASHTO=American Association of State Highway and Transportation Officials) Grading, Shape and Surface

10 Grain unit weight γ s G = V w γ w + V s γ s = (V V s )γ w + V s γ s V s = V (G G s )/γ w and γ s = G s /V s 3-Phase composition

11 Soil unit weight γ unit weight: γ = G V G... soil weight (G = M g) V... soil volume (from a calibrated cylinder/sampler) Reference configuration (voids) porosity void ratio n voids V=1 e 1 n solids V s =1

12 Porosity, void ratio porosity n: n = V v V void ratio e: e = V v V s V = V v + V s e = n 1 n or n = e 1 + e resp. Dry unit weight γ d = G s /V Dry unit weight From γ s and n = (V V s )/V = (V G s /γ s )/V follows n = 1 γ d γ s or e = γ s γ d 1 resp Sand: γ s 26.0 kn/m 3 ( ϱ = 2.65 g/cm 3 ) Clay: γ s 26.5 ± 2.0 kn/m 3

13 Water content w = M w /M s Maximum water content Ratio of masses of water and grains: unit weight: γ = γ d (1 + w) maximum water content w max : w = G w G d = G w G s From G w = γ w V v = γ w nv and G d = γ s V s = γ s (1 n)v w max = G w /G d = e γ w γ s = n 1 n γ w γ s

14 Water saturation Degree of saturation / Saturation ratio: S = w = V w = w 1 n w max V v n γ s γ w Weight γ r of (with water) fully saturated soil: γ r = γ d (1 + w max ) = γ d + nγ w Typical values Soil γ d n e w max [kn/m 3 ] soft clay stiff clay silt loose sand dense sand gravel (after Kolymbas, 1998)

15 Density Limits loose versus dense Density Limits maximum density (ρ max or e min ) vibrated and heavily loaded sample minimum density (ρ min or e max ) very loosely poured sample Only coarse grained soils!

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17 Plasticity (Atterberg limits) Fine grained soils are sensitive to water content! PL: Plastic Limit (w p ) soil ceases to behave plastic and becomes brittle LL: Liquid Limit (w l ) soil starts to flow like a liquid PI: Plasticity Index PI = LL PL Plastic limit rolling threads of 3 mm diameter (rolling drying/densification)

18 Liquid limit

19 Fall cone test Remarks to Atterberg limits w l, w p... water contents, at which the soil has a certain strength τ(w p )/τ(w l ) 100 undrained shear strength at consistency limits: c u (w l ) = 1.5 kpa, c u (w p ) 150 kpa good correlations to compressibility (C c from PI) and to undrained shear strength (c u from w)

20 Plasticity chart USCS German Standard DIN description symbol w L small plasticity L < 0.35 medium plasticity M high plasticity A > 0.50

21 Unified Classification System

22 USCS classification (USCS=Unified Soil Classification System)

23 German standard DIN 18196

24 Soil state liquidity I L : liquidity index I L : consistency index I L = w w p w l w p = w w p I P I c = w l w w l w p = w l w I P I L : < 0 (0,1) > 1 I c : > 1 (0,1) < 0 state: solid plastic liquid = 1 I L

25 Soil state density I D : density index (relative density) I D = e max e e max e min I D : (%) state: very lose lose medium dense very dense Soil state rapid assessment sand particles (d > 0.06 mm) visible to the naked eye silt (0.002 mm < d < 0.06 mm) feel abrasive between fingers (but not gritty) clay (d < mm) feel greasy plasticity moulding without cracking possible dry strength (piece of soil about 6 mm thick): silts crumbling easy between the fingers toughness test rolling of threads on the palm of the hand (3 mm diameter): silts weak threads, which breake and crumble

26 Soil consistency rapid assessment moulding in the hand: very soft if it exudes between fingers soft if it is very easy to mould and it sticks to the hand firm if it moulds easily with moderate pressure very firm if it moulds only with considerable pressure hard if it will not mould under pressure in the hand Compaction: Proctor test Compaction energy 3 layers á 25 hits Ram mass: 2,5 kg Fall height: 30 cm Modified Proctor test 4.5-times compaction energy

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29 Optimum water content Compaction quality (measured by γ d ) depends on water content w Modified Proctor test

30 GU GW typische Proctorkurven SW SU GE SE TL TM TA