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Prof. B V S Viswanadham, Department of Civil Engineering, IIT Bombay Index properties

Prof. B V S Viswanadham, Department of Civil Engineering, IIT Bombay Review

 Clay particle-water interaction

 Identification of clay minerals

 Sedimentation analysis

Prof. B V S Viswanadham, Department of Civil Engineering, IIT Bombay 20 - 40 Hydrometer analysis 0.995

130 - 150 Hydrometer is a device which is used to measure the specific 1.030 gravity of liquids. 10 - 20 4.7 φ 50

60 29 -31 φ

(All dimensions 50 are in mm)

Prof. B V S Viswanadham, Department of Civil Engineering, IIT Bombay Hydrometer Analysis -For a soil suspension, the particles start settling down right from the start, and hence the unit weight of soil suspension varies from top to bottom.

Measurement of specific gravity of a soil suspension (Hydrometer) at a known depth at a particular time provides a point on the GSD.

Prof. B V S Viswanadham, Department of Civil Engineering, IIT Bombay Process of Sedimentation of Dispersed Specimen

W VW w 1

V S WS

VS = Ws/(Gsγw) Vw = [1 -Ws/(Gsγw)]

γ γ Initial unit weight of a i = [Ws+ wVw]/1 unit volume of suspension γi = [γw + Ws(Gs-1)/(Gs)]

Prof. B V S Viswanadham, Department of Civil Engineering, IIT Bombay Process of Sedimentation of Dispersed Specimen  Size d of the particles which have settled from the surface z dz through depth z in time t X X d (From Stroke’s Law): 18µ z d = (Gs −1)γ w td Note: Above the level X – X, no particle of size > d will be present. In elemental depth dz, suspension may be uniform and particles of the size smaller than d exist. Prof. B V S Viswanadham, Department of Civil Engineering, IIT Bombay Process of Sedimentation of Dispersed Specimen  If the percentage of weight of particles finer than d (already sedimented) to the original weight of soil solids in the suspension is N′ Then:  Weight of solids per unit volume of suspension

at depth z = (N′)(W/V) (i.e. Ws = W/V)

Unit Weight of suspension after elapsing time td at depth z is γz = [γw + N′(W/V)(Gs-1)/(Gs)]

N′ = [GS/(GS-1)[γz - γw](V/W) N′ in %

Prof. B V S Viswanadham, Department of Civil Engineering, IIT Bombay Process of Sedimentation of Dispersed Specimen

 But γz = GSSγw = (1 + Rh/1000) γw

Where GSS = Sp. Gravity of Soil Suspension (Graduated on hydrometer from 0.995 – 1.030)

Rh is the reading on Hydrometer

N′ = [GS/(GS-1)](Rh/1000) (V/W)

= (GS/(GS-1) (Rh/W) For V = 1000 c.c.

Prof. B V S Viswanadham, Department of Civil Engineering, IIT Bombay Calibration or Immersion correction for Hydrometer H Vh/(AJ) x´ x´ x x y´ h/2 h y´ e h = height of the bulb y y H = Height of any reading Rh Vh/(2AJ) AJ = Area of C/S of Jar

Vh = Vol. of hydrometer Before the immersion After the immersion of hydrometer of hydrometer

he = [H+h/2+Vh/(2AJ)-Vh/AJ) = (H+h/2) - Vh/(2AJ)

Prof. B V S Viswanadham, Department of Civil Engineering, IIT Bombay Conversion of Rh = 0; Gss = 1.00 Rh into He

R = (G -1)103 h SS He1 he Rh = 30; Gss = 1.030 Plot of Rh with He – Valid for a particular He2 hydrometer

he = He1-[(He1-He2)/30]Rh  up to 4 min.

he = He1-[(He1-He2)/30]Rh – Vh/(2AJ)  after 4 min.

Prof. B V S Viswanadham, Department of Civil Engineering, IIT Bombay Hydrometer corrections

N′ = (GS/(GS-1) R/W R = Rh+ Cm ± Ct - Cd N = N′[W /W ] R = Corrected observed combined 75 T reading

Where, W75 = Wt. of soil passing 75µ

WT = Total wt. of Soil taken for combined Sieve and Hydrometer Analysis

Cm = Meniscus correction (Always + ) Because density readings increase downwards

Ct = + for T > 27°C (Rh will be less than what it should be) = - for T < 27 °C (Rh will be more than what it should be)

Cd = Always Negative (Dispersion agent concentration!!)

Prof. B V S Viswanadham, Department of Civil Engineering, IIT Bombay µ

Example on Hydrometer analysis (kaolin) Given Data: Volume of suspension = 1000 ml

Volume of hydrometer, Vh= 90 cc Weight of dry soil, Ms = 50 g Specific gravity of soil, G = 2.62 2 Cross- sectional area of jar, Aj = 31.0075 cm Room temperature, T = 27º C

Dispersing agent correction, Cm= 0.0004 Meniscus correction, Cd= 0.0034 Temperature correction, Ct = 0.9965 Viscosity of water, = 8.545 x 10-7 kN-sec/m2

Prof. B V S Viswanadham, Department of Civil Engineering, IIT Bombay Example on Hydrometer analysis (kaolin)

H’e1 = Maximum depth to centre of bulb from Rh = 0.995 = 21 cm

H’e2 = Maximum depth to centre of bulb from Rh = 1.030 = 9 cm

At t = 2 min, Rh = 1.0285

Since H’e varies linearly with reading Rh

Prof. B V S Viswanadham, Department of Civil Engineering, IIT Bombay Example on Hydrometer analysis (kaolin)

Prof. B V S Viswanadham, Department of Civil Engineering, IIT Bombay Example on Hydrometer analysis (kaolin)

Prof. B V S Viswanadham, Department of Civil Engineering, IIT Bombay Example on Hydrometer analysis

100

80

60 Percent finer (%) 40

20

0 0.001 0.01 0.1 1 Particle size (mm)

Prof. B V S Viswanadham, Department of Civil Engineering, IIT Bombay Limitations of Stroke’s law -Soil particles are not truly spherical and sedimentation is done in a jar (For d > 0.2 mm causes turbulence in water and d < 0.0002 mm Brownian movement occurs (too small velocities of settlement) --- Can be eliminated with less concentrations. -Floc formation due to inadequate dispersion -Unequal Sp.Gr of all particles (insignificant for soil particles with fine fraction)

Prof. B V S Viswanadham, Department of Civil Engineering, IIT Bombay Measures of Gradation

D60 = dia. of soil particles for which 60 % of the particles are finer. (i.e. 60 % of the particles are finer and 40 % coarser than D60)

D10: Effective Particle Size D50 : Average Particle Size

(10 % Finer and 90 % coarser than D10 size)

Prof. B V S Viswanadham, Department of Civil Engineering, IIT Bombay Measures of Gradation -Engineers frequently like to use a variety of coefficients to describe the uniformity versus the well-graded nature of soils.

D30 = 0.3 mm

Prof. B V S Viswanadham, Department of Civil Engineering, IIT Bombay Measures of Gradation Some commonly used measures are:

The uniformity coefficient Cu = D60/D10 Soils with Cu < 4 are considered to be poorly graded or uniform. Cu > 4 – 6  Well Graded Soil Coefficient of Gradation or Curvature

2 Cc = (D30 )/(D60*D10) Cc = 1- 3 Soil is well-graded.

Higher the value of Cu the larger the range of particle sizes in the soil

Prof. B V S Viswanadham, Department of Civil Engineering, IIT Bombay Typical characteristics of GSD curves

-Steep Curves ⇒ Low Cu values ⇒ Poorly graded soil (Uniformly graded).

(Cu < 5 for uniform soils)

-Flat Curves ⇒ High Cu values ⇒ Well graded soil.

-Most gap graded soils have a Cc outside the range. (an absence of intermediate particle sizes)

Prof. B V S Viswanadham, Department of Civil Engineering, IIT Bombay Typical GSDs for Residual soils Young residual Intermediate maturing Fully maturing

⇒ A residual deposit has its particle sizes constantly changing with time as the particles continue to break down…

GSD can provide an indication of soil’s history Prof. B V S Viswanadham, Department of Civil Engineering, IIT Bombay Typical GSDs for Transported soils Glacial Glacial-Alluvial

River deposits may be well-graded, uniform or gap-graded, depending up on the water velocity, the volume of suspended solids, and the river area where deposition occurred.

Prof. B V S Viswanadham, Department of Civil Engineering, IIT Bombay Grain Size Curves for different soils

Prof. B V S Viswanadham, Department of Civil Engineering, IIT Bombay Particle size distribution of Bentonite, Illite, and Kaolinite clay

After Koch (2002) Prof. B V S Viswanadham, Department of Civil Engineering, IIT Bombay Gradation

% Gravel = 0 % Sand = (100 – 60) = 40 % Silt = (60 – 12) = 48 % Clay = 12 %

Prof. B V S Viswanadham, Department of Civil Engineering, IIT Bombay Example problem Determine the percentage of gravel (G), Sand (S), Silt (M), and Clay (C) of soils A,B and C

Soil C: 0%G; 31%S; 57%M; 12%C (Well graded sandy silt) Soil B: 0%G; 61%S; 31%M; 7%C (Well graded silty sand)

Soil A: 2%G; 98%S; 0%M; 0%C (Poorly-graded sand)

Prof. B V S Viswanadham, Department of Civil Engineering, IIT Bombay Some applications of GSA in Geotechnology and construction Embankment -Selection of fill material Earth Dams

-Road Sub-Base Material -Drainage Filters -Ground Water Drainage -Grouting and Chemical Injection -Concreting Materials -Dynamic Compaction

Prof. B V S Viswanadham, Department of Civil Engineering, IIT Bombay Practical Significance of GSD -GSD of soils smaller than 0.075 mm (#200) is of little importance in the solution of engineering problems. GSDs larger than 0.075 mm have several important uses.

1) GSD affects the void ratio of soils and provides useful information for use in cement and asphalt concretes. (Well graded aggregates require less cement per unit of volume of concrete to produce denser concrete, less permeable and more resistant to weathering)

Prof. B V S Viswanadham, Department of Civil Engineering, IIT Bombay Practical Significance of GSD

2) A knowledge of the amount of percentage fines and the gradation of coarse particles is useful in making a choice of material for base courses under highways, runways, rail tracks etc., 3) To determine the activity of clay based on percentage clay fraction (<2µ) 4) To design filters (Filters are used to control seepage) and pores must be small enough to prevent particles from being carried from the adjacent soil.

Prof. B V S Viswanadham, Department of Civil Engineering, IIT Bombay Different physical states of fine-grained soil

Prof. B V S Viswanadham, Department of Civil Engineering, IIT Bombay Consistency of Fine-Grained Soils ‘Consistency’ is the property of a material which is manifested by its resistance to flow. -It represents the relative ease with which the soil may be deformed. -Degree of firmness of a soil and is often directly related to strength. -It is conveniently described as soft, medium stiff (medium firm), stiff (or firm), very stiff.

Note: These terms unfortunately are relative and have different meaning to different observers.

Prof. B V S Viswanadham, Department of Civil Engineering, IIT Bombay Consistency of Fine-Grained Soils In Soil Mechanics, it is required to determine the range of potential behaviour of a given soil type based only a few simple tests. Typical concerns are the following: i) Soils might shrink or expand excessively in an uncontrolled manner after they have been placed in geotechnical structures (roadway subgrades, dams, levees, foundation materials, etc.) ii) Soils might loose their strength and ability to carry loads safely.

Prof. B V S Viswanadham, Department of Civil Engineering, IIT Bombay Consistency of Fine-Grained Soils  Tests used to detect potential problems for coarse- grained soils (gravels and sands) are different than those used to detect potential problems for fine- grained soils (silts and clays). Coarse-Grained soils:

- Water content is generally not a major factor - Major factor leading to shrinkage is the structure of the soil skeleton.

Fine-Grained soils: Water content is a major factor Water Soils shrink Content Soils expand Gain strength Loose strength

Prof. B V S Viswanadham, Department of Civil Engineering, IIT Bombay Different physical states of fine-grained soil If the water content of a clay slurry is gradually reduced by slow desiccation, the clay passes from a liquid state through a plastic state and finally into a solid state.

The water contents at which different clays passes from one of these stats into another are very different.

∴ Water contents at these transitions can be used for Identification and Comparison of different clays.

Atterberg limits are water contents where the soil behaviour changes…

Prof. B V S Viswanadham, Department of Civil Engineering, IIT Bombay Soil-Moisture scale

Physical State Consistency Sr

LL Liquid Very Soft Soft 100 % Plastic Stiff Natural Soil Deposits PL Very 100 Semi-Solid Stiff % SL Extremely 100 Solid Stiff % Air dry Hard Soil is no longer Hygroscopic fully saturated Moisture Oven dry

Prof. B V S Viswanadham, Department of Civil Engineering, IIT Bombay Consistency of Fine-Grained Soils It was discussed that fine-grained soils have high SSAs and electrical charges on their particles. Because of this, fine-grained soils, and clays in particular can change their consistency quite dramatically with changes in water content.

Each soil type will generally have different water contents at which it behaves like a solid, semi-solid, plastic, and liquid. For a given soil, the water contents that mark the boundaries between the soil consistencies are so called Atterberg Limits. [After Swedish Soil Scientist A. Atterberg (1902)]

Prof. B V S Viswanadham, Department of Civil Engineering, IIT Bombay Consistency of Fine-Grained Soils

Atterberg Limits Atterberg limits are water contents where the soil behaviour changes. Prof. B V S Viswanadham, Department of Civil Engineering, IIT Bombay Vol. of LIQUID Sample SEMI-SOLID PLASTIC STATE STATE STATE VO A SOLI D B  Transition Stages STATE from Liquid to Solid state Transition C Vw Zone Vol. Change of G D soil = Vol. of F E moisture lost V Vd a

Vs Water Content ws wp wl wo Prof. B V S Viswanadham, Department of Civil Engineering, IIT Bombay Atterberg Limits Liquid Limit (LL) is the water content at which a soil is practically in a liquid state, but has infinitesimal resistance against flow which can be measured (2.7 kN/m2) Plastic Limit (PL) is the water content at which a soil would just begin to crumble when rolled into thread of approximately 3 mm diameter.

Shrinkage Limit (SL) is the water content at which a decrease in water content does not cause any decrease in the volume of the soil mass.

(at SL Sr =1)

Prof. B V S Viswanadham, Department of Civil Engineering, IIT Bombay Shrinkage Phenomena Water

1 Surface1 R1, R2, R3, R4, R5: 2 Radii of menisci 2 3 3 4 4 (R1 >R2>R3>R4>R5) 5 5

Idealized section through soil Imagine a compressible soil consisting of tiny grains with capillary pore space between the grains.

Prof. B V S Viswanadham, Department of Civil Engineering, IIT Bombay Shrinkage Phenomena a) When the pore spaces are completely filled with water and there is free water on the surface of the soil, the meniscus is plane surface (1) and tension in the water is zero. b) As the evaporation removes water from the surface, a meniscus begins to form in each of the pores at the surface with a resulting tension in water.

c) At some time after evaporation has started the menisci would have reduced to some position (say 2).. At this stage, tension in the water is 2Ts/R2. Soil is compressed by stress equivalent to 2Ts/R2

Prof. B V S Viswanadham, Department of Civil Engineering, IIT Bombay Shrinkage Phenomena T R2 s Ts Tension in water TW can be estimated, by equating Tensile force σ′ σ′ in water to the vertical component Ts of surface tension force, as Tw = Ts (2Ts/R2) d) As the further evaporation occurs, the fully developed meniscus in the largest pore recedes to a small diameter!! Produces increased σ′ and caused further shrinkage

Prof. B V S Viswanadham, Department of Civil Engineering, IIT Bombay Shrinkage Phenomena e) As the evaporation continues the menisci continue to recede and the tension in the water continue to increase and the compression between the soil grains and the resultant shrinkage continue to increase.

f) Eventually, the meniscus will reach the smallest radius (R5)… By the time, meniscus reduces to least possible radius of meniscus the pores in the soil will not be there to compress… Hence, Shrinkage!!!

Prof. B V S Viswanadham, Department of Civil Engineering, IIT Bombay Atterberg Limits

The Atterberg limits provide a good deal of information on the range of potential behaviour a given soil might show in the field with variations of water content.

Prof. B V S Viswanadham, Department of Civil Engineering, IIT Bombay Prof. B V S Viswanadham, Department of Civil Engineering, IIT Bombay Plasticity Index or PI

It is the range of moisture content over which soil exhibits plasticity. Plasticity is defined as that property of a material which allows it be deformed rapidly, without rupture.

IP = wL – wP (Greater the difference between wL and wP, greater is the plasticity of the soil).

Prof. B V S Viswanadham, Department of Civil Engineering, IIT Bombay Plasticity Index or PI Plasticity Index = LL – PL This measures the range of water contents over which a given soil can pull water into its macro- structure, assimilate it, and still act like a solid.  Clay soils with high SSA’s and charged particles will be able to hold a large amount of water between platelets due to their charge field and the polar nature of water molecules.

Prof. B V S Viswanadham, Department of Civil Engineering, IIT Bombay Plasticity Index or PI

Clay soils with high SSA’s and charged surfaces are able to bind/assimilate water molecules and the overall soil will still behave as a plastic solid. Such soils will have high PIs.

Soils with comparatively lower SSA’s will not be able to bind/assimilate water molecules and thus will have much smaller PI values.

Prof. B V S Viswanadham, Department of Civil Engineering, IIT Bombay Classification of soil based on PI

PI Plasticity 0 Non-Plastic < 7 Low Plastic 7 -17 Medium Plastic > 17 Highly Plastic

Prof. B V S Viswanadham, Department of Civil Engineering, IIT Bombay Laboratory determination of Liquid Limit

Two Methods:

-Casagrandes Method (After Arthur Casagrande)

-Cone Penetrometer Method

Prof. B V S Viswanadham, Department of Civil Engineering, IIT Bombay Laboratory determination of Liquid Limit

54 mm  Casagrandes Method

10mm 2mm Hard Rubber Base

2 rev/s Soil Passing 200# Sieve

Prof. B V S Viswanadham, Department of Civil Engineering, IIT Bombay Laboratory determination of Liquid Limit -Number of blows required to close the two soil halves over a distance of 13 mm is recorded and the water content of the soil is determined.

-The test is repeated several times. Each time change the water content of the sample. A graph of water content vs number of blows is plotted.

Prof. B V S Viswanadham, Department of Civil Engineering, IIT Bombay Flow curve and Flow Index Water Content Slope of the flow curve [%] = Flow Index If ++ w1, N1 (indicates rate at at which soil + looses shearing resistance with + an increase in water content) w L + + w, N Flow Curve + + N > N1; w < w1

Equation of Flow curve: w – w1 = -If [log (N/N1)]

25 No. of Blows (Log Scale)

Prof. B V S Viswanadham, Department of Civil Engineering, IIT Bombay Cone Penetrometer Test -The penetration of a standard 148g cone into a saturated soil sample is measured for 30 seconds. - If the penetration is less than 20 mm, the wet soil is taken out 50 mm and mixed thoroughly with dia. water and the test is repeated till the penetration is between 50 mm ht. 20 – 30 mm. The water content corresponds to 25 mm penetration is taken as Liquid Limit.

Prof. B V S Viswanadham, Department of Civil Engineering, IIT Bombay Determination of Plastic Limit  Water content at which the soil crumbles when rolled into threads of 3 mm diameter.

Prof. B V S Viswanadham, Department of Civil Engineering, IIT Bombay Typical Atterberg Limits for Soils

Soil type wl wp Ip Sand NP Silt 30 - 40 20 - 25 10 - 15 Clay 40 -150 25 - 50 15 -100 NP = Non-Plastic;

-Soils possessing large values of wl and Ip are said to be highly plastic or fat clays.

-Those with low wl and Ip are called lean or slightly plastic. Prof. B V S Viswanadham, Department of Civil Engineering, IIT Bombay Atterberg limit values of clay minerals with various adsorbed cations

Cation  Na+ K+ Ca++ Mg++ Mineral 

Wl [%] Ip [%] Wl [%] Ip [%] Wl [%] Ip [%] Wl [%] Ip [%]

Kaolinite 29 1 35 7 34 8 39 11

Illite 61 27 81 38 90 50 83 44

Montmorill 344 251 161 104 166 101 158 99 onite

Prof. B V S Viswanadham, Department of Civil Engineering, IIT Bombay Liquidity Index and Consistency Index   w − wp  wl − w I L =   Ic =    I p   I p 

Solid Semi Plasti Liqui Solid c d w

0 SL PL 0 1

I > 1 c Ic = 1 Ic = 0 Ic < 0 Prof. B V S Viswanadham, Department of Civil Engineering, IIT Bombay Soil classification based on soil consistency

Ic Il Consistency >1 <0 Very Stiff 1 – 0.75 0 – 0.25 Stiff 0.75 –0.50 0.25 – 0.50 Medium soft 0.50 – 0.25 0.50 – 0.75 Soft 0.25 -0 0.75 – 1.0 Very Soft < 0 > 1.0 Liquid state

Prof. B V S Viswanadham, Department of Civil Engineering, IIT Bombay  Indicates the rate of loss of Toughness Index I t shear strength upon increase With the assumption thatin wflow % line is straight between wl and wp and Shearing resistance α No. of blows

Nl = kSl Np = kSp ; wl = -If log Nl+C --- (1) wp = -If log Np+C --- (2)

S p  I p = I f log  It <1 Soil is easy to  Sl  crumble or pulverize.

I p S p  It = = log  It = 1 – 3 for most clay soils I f  Sl 

Prof. B V S Viswanadham, Department of Civil Engineering, IIT Bombay Distinction between Silt and Clay

Prof. B V S Viswanadham, Department of Civil Engineering, IIT Bombay