1 Soil Classification Prof Neelam Belani Assistant Professor, Civil Engineering Department IT,NU.

Soil Classification

Prof Neelam BelaniAssistant Professor, Civil Engineering

DepartmentIT,NU.

Objectives

To develop a systematic way to describe and classify soils;

To assign symbols.

To group soils of similar geotechnical characteristics; and

Major Soil Groups

0.002 200632.360.075

Grain size (mm)

BoulderClay Silt Sand Gravel Cobble

Fine grain soils

Coarse grain soils

Granular soils or Cohesionless soils

Cohesive soils

Grain Size Distribution

To know the relative proportions of different grain sizes.

An important factor influencing the geotechnical characteristics of a coarse grain soil.

Not important in fine grain soils.

Significance of GSD:

Grain Size Distribution

In coarse grain soils …... By sieve analysis

Determination of GSD:

In fine grain soils …... By hydrometer analysis

Sieve Analysis Hydrometer Analysis

soil/water suspension

hydrometer

stack of sieves

sieve shaker

Grain Size Distribution Curve

can find % of gravels, sands, fines

define D10, D30, D60.. as above.

0

20

40

60

80

100

0.001 0.01 0.1 1 10

Grain size (mm)

D30

sievehydrometer

D10 = 0.013 mmD30 = 0.47 mmD60 = 7.4 mm

sands gravelsfines

% P

assi

ng

Well or Poorly Graded Soils

Well Graded Soils Poorly Graded Soils

Wide range of grain sizes present

Gravels: Cc = 1-3 & Cu >4

Sands: Cc = 1-3 & Cu >6

Others, including two special cases:

(a) Uniform soils – grains of same size

(b) Gap graded soils – no grains in a specific size range

Relative Density (Dr)

Measure of how densely the grains are packed in a coarse grain soil in %.

0 100

Loosest Densest

minmax

max

ee

eeDr

Also known as density index (ID).

Granular Soil Consistencies

As per AS1726 - 1993

Relative Density (%) Consistency Term

0-15

15-35

35-65

65-85

85-100

Very loose

Loose

Medium dense

Dense

Very dense

Atterberg Limits

Border line water contents, separating the different states of a fine grained soil

Liquidlimit

Shrinkagelimit

Plasticlimit

0water content

liquidsemi-solid

brittle-solid

plastic

Atterberg Limits

Liquid Limit (wL or LL):

Clay flows like liquid when w > LL

Plastic Limit (wP or PL):

Lowest water content where the clay is still plastic

Shrinkage Limit (wS or SL):

At w<SL, no volume reduction on drying

Plasticity Index (PI)

Range of water content over which the soil remains plastic

Liquidlimit

Shrinkagelimit

Plasticlimit

0water content

plastic

Plasticity Index = Liquid Limit – Plastic Limit

Classifying Fines

Purely based on LL and PI

20 100500

20

0

40

60

Liquid Limit

Liqu

id L

imit

A-Line

PI=0.73(LL-20)

Silts

Clays

High plasticity

Low plasticity

35

Intermediate plasticity

IS 1726 – 1993 Classification

0 5 12 50 100

% of fines

fine grain soilscoarse grain soils

X: Coarse

G = Gravel

S = Sands

Y: Fines

M = Silts

C = Clays

A: Gradation

W = well graded

P = poorly graded

B: Plasticity

H = LL > 50

I = 35 < LL < 50

L = LL < 35

XA

e.g., GP

YB

e.g., CHXY

e.g., SM

XA-XY

e.g., GP-GC

Summary

Sieve analysis – for coarse grain soils Hydrometer analysis - for fine grain soils

Classify coarse by GSD and fines by Atterberg limits (PI-LL

chart)

.

16

Classification of Soils

17U.S. Army Corps of Engineers (Triangular Chart Classification, 1943)

18

Arthur CasagrandeBorn: August 28, 1902

Migrated to US in US, as research assistant at Bureau of Public Roads, with Karl Terzaghi at M. I. T.

Worked on soil classification, shear test and frost action on soil

Initiated soil mechanics at Harvard University, 1932

1 Soil Classification Prof Neelam Belani Assistant Professor, Civil Engineering Department IT,NU.

Documents

Transcript of 1 Soil Classification Prof Neelam Belani Assistant Professor, Civil Engineering Department IT,NU.