Class 1 Moisture Content - Specific Gravity ( Geotechnical Engineering )

Civil Engineering - Texas Tech University

CE 3121: Geotechnical Engineering Laboratory

Introduction

Moisture Content, Unit Weight, Specific Gravity

and Phase Relationships

Abdulrahman Alhabshi

Sources:

Soil Mechanics – Laboratory Manual, B.M. DAS (Chapters 2 - 3)

1


Handouts: Syllabus, Report Format

Class website:

http://www.classes.ce.ttu.edu/ce3121/

Significance of the Class

Lab No.1: Moisture Content, Specific gravity

and Unit Weight of soil

Background: Phase Relationship

Class Outlines

2





Syllabus

Text books:

Soil Mechanics: Laboratory Manual by Braja M. Das

Lecture Notes

ASTM Standards 2005

Class organization

1 hour class

2 hours lab

Class Schedule (No classes Oct 18 & 19)

Attendance 3


Report Format

Each group will submit one report per lab

Reports are due one day before the class at 9am

(Ex: for Wed. class, submit report on Tuesday at 9am)

All reports should follow the report format Title and Table of Contents

Purpose & Objective

Apparatus & Procedures

Deviation from ASTM Standards

Table of results

Figures

Sample Calculations

Discussion and Conclusion

4


Report Format - Conclusion

Report your results (use a table)

Do the results fall within the expected range

or not? (Check tables and match your results)

If not, Explain why (what went wrong?)

5


Significance of this Class

Why do you need to learn about soils?

Almost all structures are either constructed of soil, supported on soil, or both.

Who must be concerned with soils?

Civil engineers (structural, environmental and geotechnical) must have basic understanding of the soil properties in order to use them effectively in construction.

6


Transcosna Grain Elevator, Canada

Oct. 18, 1913

West side of foundation sank 24-ft 7


Settlement

Palacio de las Bellas, Artes,

Mexico City

Leaning Tower, Pisa

8

http://en.wikipedia.org/wiki/Image:Leaning-tower-of-pisa.jpg


Shear Failure – Slope Stability

9


Organization of the Lab Tests

Physical (Soil Characteristics)

Mechanical

Moisture

Content

Unit Weight

Compressibility Permeability Specific

Gravity Gradation

Atterberg

Limits

Strength

(Shear)

Geotechnical engineering

Structural engineering

Pavement engineering

Environmental engineering

Geotechnical engineering

Structural engineering

Pavement engineering

Soil Properties

(Soil Classification)

10


Today’s Lab

Determination of unit weight (density)

Determination of moisture content

Determination of specific gravity

Establishing the phase (weight-volume) relationship diagram

Calculation of: Dry unit weight

Void ratio

Porosity

Degree of saturation

11


1- Unit Weight, g

Take several measurements for diameter and

height

Take the average for H, D

Calculate g

V

Mg

HD

V

where

4

2

H

D

12


2- Moisture Content, w

Definition: Moisture content is an indicator of the

amount of the water present in soil.

Moisture content, w(%)

ASTM 2216 (Conventional Oven Method)

ASTM D 4643 (Microwave Oven Method)

3 minutes at 50% Power (mass ≈ 50 g)

T

w

s

w

M

Mnotbut

M

Mw 100%

Mw – Mass of waters

Ms – Mass of solids

MT – Total mass

13


2- Moisture Content – Sample Size

Minimum mass of moist material selected to be

representative of the total samples:

Maximum Particle Size

(95-100% Passing)

Standard Sieve

Size

Recommended Min. Mass

of moist specimen

2 mm or less # 10 20 g

4.75 mm # 4 100 g

9.5 mm 3/8-in 50 g

19.0 mm ¾-in 250 g

37.5 mm 11/2 -in 1000 g

75.0 mm 3-in 5000 g

14


2- Moisture Content - Procedure

Video Demos


2- Moisture Content – Sample Calculation

16


3- Specific Gravity, Gs

Definition; specific gravity, Gs, of soil solids is the ratio of the density of the aggregate soil solids to the density of water.

Mathematically,

ASTM D 854

This method is applicable for soils composed of “Particles smaller than 4.75mm in size”.

w

ssws

w

w

s

s

w

ss

M

MGhenceVVbut

VM

VM

G

;

g w = 1 g/cm3 at 40C

or w = 62.4 lb/ft3

17


3- Specific Gravity – Sample Size

The procedure employs Archimedes’s principle “A body submerged in water will displace a volume of water equal to its own

volume.”

The key to successful application of this procedure is the

removal of entrapped air

Recommended mass for test specimen

Soil Type Specimen Dry Mass (g)

250 mL Pycnometer

Specimen Dry Mass (g)

500 mL Pycnometer

SP, SP-SM 60 ± 10 100 ± 10

SP-SC, SM, SC 45 ± 10 75 ± 10

Silt or Clay 35 ± 5 45 ± 10

18


3- Specific Gravity - Apparatus

Report Gs in terms of GS (200C) = GS (Ti0C) x A

A – From Table 3-2 Pg 12

See Example in Table 3-3 Pg 13

19

Video Demos


3- Specific Gravity – Expected Values

Expected Values for Gs

Type of Soil Gs

Sand 2.65 - 2.67

Silty sand 2.67 – 2.70

Inorganic clay 2.70 – 2.80

Soils with mica or iron 2.75 – 3.00

Organic soils < 2.00

20


Phase Relationships

Three phase diagram

Weight relationships

Volumetric relationships

Weight – Volume relationship

Examples

Phase Relationships

21

Phase Relationships: A 3-Phase Material

Solid

Water Air

22


The Mineral Skeleton

Volume

Solid Particles

Voids (air or water)

23


Three Phase Soil

(Partially Saturated)

Solids

Air

Water

Mineral Skeleton Idealization:

Three Phase Diagram

24


Two Phase Soil

(1) Fully Saturated Soils

Fully Saturated

Water

Solids

Mineral Skeleton

25


Two Phase Soil (2) Dry Soils [Oven Dried]

Mineral Skeleton Dry Soil

Air

Solids

26


Weight-Volume Relationships

Volume Weight

Solids

Air

Water WT

Ws

Ww

Wa~0

Vs

Va

Vw

Vv

VT

27


Weight Relationships (weight -ratios)

Weight ratios

Moisture Content, w Specific Gravity, Gs

Weight Components:

Weight of Solids = Ws

Weight of Water = Ww

Weight of Air, Wa ~ 0

%100(%), s

w

W

WwContentWater

Solids

Air

Water WT

Ws

Ww

Wa~ 0

28


Specific Gravity (weight ratio)

WaterofVolumeEqualanofWeight

ceSubsaofWeightGravitySpecific

tan

WaterofWeightUnit

ceSubsaofWeightUnitGravitySpecific

tan

%100, ws

s

w

s

s

sV

WV

W

GGravitySpecificgg

Unit weight of Water, gw or w

gw = 1.0 g/cm3 (strictly accurate at 4° C)

gw = 62.4 pcf

gw = 9.81 kN/m3

29


Typical Values for Specific Gravity, Gs

30


Volumetric Relationships (Vol. ratios)

Volumetric ratios

Void ratio, e

Porosity, n(%)

Degree of Saturation, S (%)

Volume Components:

Volume of Solids = Vs

Volume of Water = Vw

Volume of Air = Va

Volume of Voids = Va + Vw = Vv

Solid

Air

Water

Vs

Va

Vw

Vv

VT

31


Volumetric Relationships

s

v

V

VeRatioVoid ,

%100(%), V

w

V

VSSaturationofDegree

%100(%), T

v

V

VnPorosity

32


Weight-Volume Relationships

Steps to develop the weight-volume relationship

Separate the three phases

The total volume of a soil

Assuming the weight of air (Wa) to be negligible, the

total weight is then given as

awsvs VVVVVV

wsT WWW

33


Example:

Determine moisture content, void

ratio, porosity and degree of

saturation of a soil core sample.

Also determine the dry unit

weight, gd

Data:

Weight of soil sample, MT = 1013g

Vol. of soil sample, VT = 585.0cm3

Specific Gravity, Gs = 2.65

Moisture Content, w = 12.1%

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Solid

Air

Water

Ma~0

Volumes Weights

1013.0g 585.0cm3

904.0g

Gs =2.65

109.0g

341.1cm3

109.0cm3

243.9cm3

134.9cm3

gw = 1.0 g/cm3

Sample Calc. gMMM sTw 1099041013

39.134)1091.341(585)( cmVVVV wsTa 3

3109

)/(0.1

)(109cm

cmg

gWV

V

W

w

ww

w

ww

gg 3

31.341

)/(0.165.2

)(904cm

cmg

g

G

WV

V

WG

ws

ss

ws

ss

gggVVV awv 9.2439.134109

35

gw

MM

MwMMwM

insubstitute

MwMM

Mwbut

MMM

Ts

sssT

sw

s

w

swT

904121.01

1013

1

)1(

)1()2(

)2(

)1(

w

=12.1%


Sample Calculation (cont.)

gw

MM

MwMMwM

insubstitute

MwMM

Mwbut

MMM

Ts

sssT

sw

s

w

swT

904121.01

1013

1

)1(

)1()2(

)2(

)1(

gVVV awv 9.2439.134109

3

31.341

)/(0.165.2

)(904cm

cmg

g

G

WV

V

WG

ws

ss

ws

ss

gg

3

3109

)/(0.1

)(109cm

cmg

gWV

V

W

w

ww

w

ww

gg

39.134)1091.341(585)( cmVVVV wsTa

gMMM sTw 1099041013

1

2

3

4

5

6

36


Weight-Volume Relationships (cont.)

From the previous figure we can find:

Moisture content, w

Void ratio, e

Porosity, n

Degree of saturation, S

Dry unit weight, gd

355.1

585

904

cm

g

V

W

T

sd g

%7.441009.243

109

v

w

V

VS

715.01.341

9.2433

3

cm

cm

V

Ve

s

v

%7.41100)(0.585

)(9.2433

3

cm

cm

V

Vn

T

v

%1.12100)(904

)(109

g

g

W

Ww

s

w

37


Weight-Volume Relationships (cont.)

38


Typical Unit weights

39

Civil Engineering - Texas Tech University 40


This Report Should Include

1. Unit Weight of Soil, g

2. Water Content, w

3. Specific Gravity, Gs

4. Three Phase Diagram

5. Void ratio, e

6. Porosity, n

7. Degree of Saturation, S

8. Dry Unit Weight, gd

41