Class 2 Grain Size Analysis ( Geotechnical Engineering )

Civil Engineering - Texas Tech University

CE 3121: Geotechnical Engineering Laboratory

Class 2

Grain Size Analysis

Sources:

Soil Mechanics – Laboratory Manual,B.M. DAS (Chapters 4 & 5)

Soil Properties, Testing, Measurement, and Evaluation, C. Liu, J. Evett


Grain size Analysis

Chapter 4: Mechanical Method (Sieve Analysis)

Chapter 5: Hydrometer Method

Class Outlines


2- Grain size Analysis

The knowledge of sizes of solid particles

comprising a certain soil type and their

relative proportion is useful because it is used

in;

Soils classification

Soil filter design

Predictions the behavior of a soil with respect

to shear strength, settlement and permeability


Grain size Analysis (Continue)

Two types of grain size analyses are typically

performed

Mechanical analysis also know as sieve

analysis

Hydrometer analysis


Sieve Analysis

ASTM D 421

Applicable for soils that are mostly granular

with some or no fines

The U.S. No. 200 sieve (0.074mm or

0.0029in) is the smallest sieve size typically

used in practice

Small size is 500g (why?)


Sieve Analysis (Cont.)



3/8”, ¼” sieves is the size

of the opening

No.10 sieve …. has 10

apertures per linear inch

Use sieves No. 3/8”, No.4,

No.10, No.40, No.140 &

No.200


Grain Size Distribution Curves

D60

D30

D10

0.8 mm

0.4 mm

0.15 mm

0.15 mm

0.8 mm 5.3

0.4

0.15 0.8 1.33



D60 - the diameter corresponding to 60% finer in the

particle-size distribution curve

D10 – effective size

Cu – coefficient of gradation,

Cc – coefficient of curvature,

10

60

D

Dcu

1060

2

30

DD

Dcc

Note:

If cu is relatively large, it indicates a well graded soil. Cu = 1 indicates

that the soil grains are of approximately equal sizes.


Hydrometer Analysis

ASTM D422

This method is generally used to determine the particle-size distribution for soils with small grain sizes < 0.075 mm (No. 200)

The lower limit of the particle size determined by this procedure is about 0.001mm

In the lab we will use ASTM 152-H Hydrometer (?)

This method is based on Stoke’s law “The larger the grain size, the greater its settling velocity in a fluid”

The sample size is 50g passing #10 (why?)

waterofityvisDv ws cos:;18

)( 2


Hydrometer Analysis (Cont.)

L =30


Hydrometer Test (Cont.)

A Hydrometer reading of 30 means that there

are 30 g of soil solids in suspension per

1000cc of soil-water mixture at a temperature

of 200C

Take reading at 15, 30, 60 seconds then at 2,

5, 15, 30 and 60 minutes


Composite Corrections

Fm – Meniscus Correction

Zero Correction, Fz Accounts for the effect of using a deflocculating agent

Temperature Correction, FT FT = - 4.85 + 0.25T (T between 15 – 280C)

Composite Correction = Fm + Fz + FT

Fm


Hydrometer Test (Procedure)

1. Prepare a deflocculating (dispersing) agent

Use a 4% solution of Sodium

hexametaphophate (Calgon)

Add the 40g of Calgon in 1000cc of distilled

water and mix thoroughly

2. Use 45±5g of soil passing #10

3. Take 125cc of the mixture prepared in (1)

and add it to the soil in (2) and let it soak for

about 8 – 12hours


Hydrometer Test (Calculation - pp 30)

R – Hydrometer reading (col 2)

Rcp – corrected hydrometer reading for calculation of

percent finer (col 3)

Rcp = R + FT – Fz

Percent finer (col 4) =

RcL - Corrected reading for determination of effective

length (col 5) & Find L from Table 5-1 pp 26

RcL = R + Fm

Determine D =

s

cp

W

Ra a = correction for Gs see

Table 5-3 pp 30

Assume Gs = 2.65

(min)

)(

t

cmLA