project class

Conducted by: Offered to :

Riyadh, Saudi Arabia, 2019-2020

Dr. Mohamed Ezzat Assistant professor of Civil Eng.

Department of Engineering Management

College of Engineering.

Prince Sultan University

Undergraduate Students –Senior Level.

Engineering Management Department.

College of Engineering.

Prince Sultan University

2nd semester- Year 2019-2020.

EM 306 : Soil Mechanics and Foundations

Construction Management Program (CMP)

Consolidation in Soil

Topic No. 8

Topic (8)

 Page :1 Dr. Eng. Mohamed Ezzat EM306: Soil Mechanics and Foundations

TENTATIVE WEEKLY COURSE SCHEDULE WEEK UNIT/ TOPIC

Number of Contact

hours

1 Introduction 5

2 Soil Formation 5

3 Engineering Properties of Soil 5

4 Soil Exploration 5

5 Soil Compaction 5

6 Water in Soil 5

7 Stress in soils 5

8-9 Consolidation of soil 5

10-11 Shear Strength of soil 10

12-13 Bearing Capacity and Shallow Foundations 10

14 Deep Foundations 5

15 Lateral Earth Pressure & Retaining Structures As Scheduled

 Consolidation in Soil Topic No. 8

CONSOLIDATION OF THE SOIL

 Consolidation in Soil Topic No. 8

 Page :2 Dr. Eng. Mohamed Ezzat EM306: Soil Mechanics and Foundations

CONSOLIDATION OF THE SOIL The volume of a soil mass is decreased under stress. This decrease is known

as compression, and the capacity of soil to decrease in volume under stress is

know as compressibility.

If voids are filled with air, compression will occur rapidly,

since air is compressible and can escape easily from the

voids (called Elastic settlement). On the other hand, if

the voids are filled with water, decrease in volume can

only take place when the water is expelled out of the

voids (called Primary settlement). In partially saturated

soils, compression is accompanied by compression of

air and expulsion of water.

 Consolidation in Soil Topic No. 8

 Page :3 Dr. Eng. Mohamed Ezzat EM306: Soil Mechanics and Foundations

Total compression = Elastic settlement + Primary settlement +

Secondary settlement.

Where:

 Elastic (Immediate) settlement: Occurs due to

compression of air.

 Primary (Consolidation) settlement: Occurs due to

expulsion of water.

 Secondary (Creep) settlement: Occurs due to

rearrangement of soil particles.

 Consolidation in Soil Topic No. 8

 Page :4 Dr. Eng. Mohamed Ezzat EM306: Soil Mechanics and Foundations

IMMEDIATE (ELASTIC) SETTLEMENT

7.1eqn 1

2

u si

E qBCS

 

 Si = immediate settlement

 Cs = shape & foundation rigidity factor (Table 7.1 &

7.2)

 q = acting load on the foundation area (Stress)

 B = width or diameter of foundation

  =Poisson’s ratio for the applied stress range

 Eu = undrained elastic modulus of clay

• Eu may be evaluated using the results of

undrained triaxial compression tests

• Eu = 500 Cu ~ 1500 Cu (Empirical Range)

• Cu = soil cohesion shear strength as

determined from the undrained tests

 Consolidation in Soil Topic No. 8

 Page :5 Dr. Eng. Mohamed Ezzat EM306: Soil Mechanics and Foundations

A square 3m x 3m rigid footing is resting on a deep clay deposit. The

footing is to carry a concentrated load of 1800 kN. The undrained elastic

modulus of clay Eu is estimated to be 40MPa, and the Poisson’s ratio of the

clay is 0.5. Determine the expected immediate settlement beneath the

centre of the footing.

3.0 x3.0 m

Clay Deposit

µ = 0.5

E = 40000 kN/m2

P = 1800 kN

Example 1

 Consolidation in Soil Topic No. 8

 Page :6 Dr. Eng. Mohamed Ezzat EM306: Soil Mechanics and Foundations

From eqn 7.1

Si = Cs q B ( 𝟏−𝝁𝟐

𝑬𝒖 )

From Table 7.1, Cs = 0.82

Si = (0.82) ( 𝟏𝟖𝟎𝟎 𝒌𝑵

𝟑 𝒎 (𝟑 𝒎) ) (3 m) (

𝟏−𝟎.𝟓𝟐

𝟒𝟎∗𝟏𝟎𝟑 𝒌𝑵/𝒎𝟐 )

Si = 0.0092 m = 9.2 mm

Solution:

 Consolidation in Soil Topic No. 8

 Page :7 Dr. Eng. Mohamed Ezzat EM306: Soil Mechanics and Foundations

Typical values of modulus of elasticity Typical values of poisson ratio

 Consolidation in Soil Topic No. 8

 Page :8 Dr. Eng. Mohamed Ezzat EM306: Soil Mechanics and Foundations

PRIMARY (CONSOLIDATION) SETTLEMENT It is a gradual compression due to expulsion of water from soil voids accompanied

by transfer of stress from pore water to soil particles caused by application of

sustained external stress is known as consolidation.

The rate of consolidation is governed by the rate at which pore water escapes, and

hence it is directly related to soil permeability.

 Consolidation in Soil Topic No. 8

 Page :9 Dr. Eng. Mohamed Ezzat EM306: Soil Mechanics and Foundations

PRIMARY (CONSOLIDATION) SETTLEMENT

(a) Consolidation test using Odometer:

In order to determine the compression

characteristics of a soil, a consolidation

test is carried out in an apparatus called

oedometer

 Consolidation in Soil Topic No. 8

 Page :10 Dr. Eng. Mohamed Ezzat EM306: Soil Mechanics and Foundations

CONSOLIDATION TEST

https://www.youtube.com/watch?v=5kuw6-axQIw

 Consolidation in Soil Topic No. 8

 Page :11 Dr. Eng. Mohamed Ezzat EM306: Soil Mechanics and Foundations

o Diameter of test specimen = 6.35 cm

o Initial height of specimen = 1.98 cm

o Specific gravity of solids = 2.72

o Dry mass of specimen = 75.91 g

o Pressure versus deformation dial

readings are as given in the following

table

Pressure,

p

(kPa)

Initial deformation

dial reading at

beginning of first

loading (mm)

Deformation dial

reading representing

100% primary

consolidation (mm)

0 0 0

25 0 0.401

50 0 0.721

100 0 1.244

200 0 1.933

400 0 2.908

800 0 4.013

A clayey soil obtained from the field was subjected to a laboratory consolidation test. The

test results are as follows:

 Determine initial void ratio & e-log p curve

Example 2

 Consolidation in Soil Topic No. 8

 Page :12 Dr. Eng. Mohamed Ezzat EM306: Soil Mechanics and Foundations

Volume of solid in specimen (Vs) = 𝑫𝒓𝒚 𝒎𝒂𝒔𝒔 𝒐𝒇 𝒔𝒐𝒍𝒊𝒅

𝑼𝒏𝒊𝒕 𝒎𝒂𝒔𝒔 𝒐𝒇 𝒔𝒐𝒍𝒊𝒅

= 𝑫𝒓𝒚 𝒎𝒂𝒔𝒔 𝒐𝒇 𝒔𝒐𝒍𝒊𝒅

𝒔𝒆𝒄𝒊𝒇𝒊𝒄 𝒈𝒓𝒂𝒗𝒊𝒕𝒚 𝒐𝒇 𝒔𝒐𝒍𝒊𝒅𝒔 (𝒖𝒏𝒊𝒕 𝒎𝒂𝒔𝒔 𝒐𝒇 𝒘𝒂𝒕𝒆𝒓)

Vs = 𝟕𝟓.𝟗𝟏 𝒈

𝟐.𝟕𝟐 (𝟏.𝟎 𝒈 /𝒄𝒎𝟑) = 27.91 cm3

Initial volume of specimen (Vt) = 𝟏.𝟗𝟖 𝝅(𝟔.𝟑𝟓 𝒄𝒎)𝟐

𝟒 Vt = 62.74 cm3

Step (1): Determine The initial Void ratio:

Initial volume of voids in specimen (Vv) = (62.74 – 27.91) cm 3

Vv = 34.83 cm 3

= 𝟑𝟒.𝟖𝟑

𝟐𝟕.𝟗𝟏 = 1.248Initial void ratio (eo) =

𝑽𝒗

𝑽𝒔

GS = γ𝒔

γ𝒘

γd = 𝑾𝒔

𝑽𝒕

Reminder

Step (1)

Solution:

 Consolidation in Soil Topic No. 8

 Page :13 Dr. Eng. Mohamed Ezzat EM306: Soil Mechanics and Foundations

Step (2) develop the e-log p curve: 1. one must determine the height of solids in the specimen

height of solid in specimen (Hs) = 𝑽𝒔

𝒂𝒓𝒆𝒂 𝒐𝒇 𝒔𝒑𝒆𝒄𝒊𝒎𝒆𝒏

Hs = 𝟐𝟕.𝟗𝟏

𝝅(𝟔.𝟑𝟓 𝒄𝒎)𝟐 /𝟒

Hs = 0.881 cm

Pressure,

p

(kPa)

Initial deformation

dial reading at

beginning of first

loading (mm)

Deformation dial

reading representing

100% primary

consolidation (mm)

0 0 0

25 0 0.401

50 0 0.721

100 0 1.244

200 0 1.933

400 0 2.908

800 0 4.013

2. The change in thickness of the specimen (∆H)

can be found by subtracting the initial

deformation dial reading from the deformation

dial reading representing 100% primary

consolidation.

For the 25 kPa pressure,

∆H = (0.401 – 0) = 0.0401 cm

Step (2)

Solution:

 Consolidation in Soil Topic No. 8

 Page :14 Dr. Eng. Mohamed Ezzat EM306: Soil Mechanics and Foundations

dividing ∆H by Hs

Ex:

For the 25 kPa pressure,

∆e = 𝟎.𝟎𝟒𝟎𝟏 𝐜𝐦

𝟎.𝟖𝟖𝟏 𝐜𝐦 = 0.046

4.Finally, e can be computed

by subtracting ∆e from eo

Ex:

For the 25 kPa pressure,

e = 1.248 – 0.046 = 1.202

Pressure

p (kPa)

Initial

deformation

dial reading at

beginning of

first loading

(mm)

Deformation

dial reading

representing

100% primary

consolidation

(mm)

H

(cm) e Void

ratio

(e)

0 0 0 0 0 1.248

25 0 0.401 0.0401 0.046 1.202

50 0 0.721 0.0721 0.082 1.166

100 0 1.244 0.1245 0.141 1.107

200 0 1.933 0.1933 0.219 1.029

400 0 2.908 0.2908 0.330 0.918

800 0 4.013 0.4013 0.456 0.792

3. Change in void ratio (∆e) can be determined by:

∆H =Rn- R0 ∆e = ∆H/ Hs

e = eo - ∆e

Solution:

 Consolidation in Soil Topic No. 8

 Page :15 Dr. Eng. Mohamed Ezzat EM306: Soil Mechanics and Foundations

Hs = 0.881 cm

 Step (5): Plot The e-log p curve is prepared by plotting void ratio e and

pressure, with the latter on a log scale

Solution:

 Consolidation in Soil Topic No. 8

 Page :16 Dr. Eng. Mohamed Ezzat EM306: Soil Mechanics and Foundations

1. Stress – Strain curve 3.(e – log P) curve2. Void Ratio–Pressure Plots

CONSOLIDATION TEST OUTCOMES

∆e

P

Used to Obtain mv

e

P

Used to Obtain av

Log P

av = ∆𝒆

∆𝝈 mv =

𝒂𝒗

𝟏+𝒆𝒐 cc =

𝒆𝟏 − 𝒆𝟐

𝒍𝒐𝒈 (𝒑𝟐/𝒑𝟏)mv = 𝑺𝒕𝒓𝒂𝒊𝒏

𝑺𝒕𝒓𝒆𝒔𝒔 =

∆𝑯𝒇

𝑯𝒐

∆𝝈𝒇

Used to Obtain CC

aV (Coefficient of compressibility)mV (Coefficient of volume change) Cc (Compression index)

 Consolidation in Soil Topic No. 8

 Page :17 Dr. Eng. Mohamed Ezzat EM306: Soil Mechanics and Foundations

 To determine if the clay is

normally consolidated (NC),

it is necessary to know the

present effective overburden

pressure (po = γ*h):

 This pressure is the

result of the effective

weight of soil above mid-

height of the

consolidating clay layer

NORMALLY CONSOLIDATED CLAY

o With the e-log p curve developed from laboratory test, the point corresponding

to 0.4 eo is determined

 Consolidation in Soil Topic No. 8

 Page :18 Dr. Eng. Mohamed Ezzat EM306: Soil Mechanics and Foundations

(a) Normally consolidation clay

σ‘c = σ‘o & Over consolidation (OCR) = 𝝈′𝒄

𝝈′𝒐 = 1

(b) Over consolidation clay

σ‘c > σ‘0 OCR > 1

(c) Under consolidation clay

σ‘c < σ‘o Where:

Overburden stress (σ’o) = Σγ.H

TYPE OF CLAY

σ ‘ c

 Consolidation in Soil Topic No. 8

 Page :19 Dr. Eng. Mohamed Ezzat EM306: Soil Mechanics and Foundations

SETTLEMENT OF LOADS ON CLAY DUE TO PRIMARY CONSOLIDATION

 Consolidation in Soil Topic No. 8

 Page :20 Dr. Eng. Mohamed Ezzat EM306: Soil Mechanics and Foundations

a. For Normally Consolidated Clay

(a) Normally consolidation clay

σ‘c = σ‘o & Over consolidation (OCR) = 𝝈′𝒄

𝝈′𝒐 = 1

cc = 𝒆𝟏 − 𝒆𝟐

𝒍𝒐𝒈 (𝒑𝟐/𝒑𝟏) eqn 7.4

Sc = Cc 𝑯

𝟏+𝒆𝒐 (log

𝒑

𝒑𝒐 ) eqn 7.18

SETTLEMENT OF LOADS ON CLAY DUE TO PRIMARY CONSOLIDATION

Sett. (∆Hf) = mv . ∆σ . H

Sett. = Σ 𝟏

𝑬 . ∆σ . H

 Consolidation in Soil Topic No. 8

 Page :21 Dr. Eng. Mohamed Ezzat EM306: Soil Mechanics and Foundations

cc = 0.009 (L.L.

– 10)

b. For Over Consolidated Clay

 Overconsolidated clay is generally less

compressible

 The analysis of clay for consolidation

settlement differs whether the clay is

normally consolidated or overconsolidated

(b) Over consolidation clay

σ‘c > σ‘0 OCR > 1

 Consolidation in Soil Topic No. 8

 Page :22 Dr. Eng. Mohamed Ezzat EM306: Soil Mechanics and Foundations

Example 3

For the shown footing in figure, it is

required to calculate the expected

compression of the clay layer due

to the shown loading condition.

1600 kN

1.5 m

1.5 m

4.5 m

3.0 * 3.0 m

G.W.T

Dry Sand

Gs = 2.65

e = 0.52

Clay

Gs = 2.75, e = 0.52

mv = 1.85 * 10 -4 m2/kN

 Page :23 Dr. Eng. Mohamed Ezzat EM306: Soil Mechanics and Foundations

 Consolidation in Soil Topic No. 8

Solution:

∆σ = 𝟏𝟔𝟎𝟎

𝟔.𝟕𝟓 ∗𝟔.𝟕𝟓 = 35.1 kN/m2

∆H = mv . ∆σ . H

 ∆H = 1.85 * 10-4 * 35.1 * 4.5

→ ∆H = 0.029 m = 2.9 cm

1600 kN

1.5 m

1.5 m

4.5 m

3.0 * 3.0 m

G.W.T

Dry Sand

3.75

Clay

mv = 1.85 * 10 -4 m2/kN

6.75 * 6.75 m

Sandstone

∆σ

Step (1): Determine the external stress

Step (2): Determine the Settlement

 Page :24 Dr. Eng. Mohamed Ezzat EM306: Soil Mechanics and Foundations

 Consolidation in Soil Topic No. 8

Example 4

For the shown footing in figure, it

is required to calculate the

expected compression of the clay

layer due to the shown loading

condition.

4.0 * 6.0 m

G.W.T

N.L. Clay

γsat = 18.7 kN/m 2

e = 1.1 L.L. = 60%

1.0

5.0

100 kN/m2

Sandstone

 Page :25 Dr. Eng. Mohamed Ezzat EM306: Soil Mechanics and Foundations

 Consolidation in Soil Topic No. 8

Solution:

4.0 * 6.0 m

G.W.T

N.L. Clay

γsat = 18.7 kN/m 2, e = 1.1 , L.L. = 60%

1.0

5 .0

m

100 kN/m2

Sandstone

z =

2 .5

6.5 * 8.5m

∆σ

σo = 1 * 18.7 + 2.5 * 8 = 40.5 kPa

∆σ = 𝟏𝟎𝟎 ∗ 𝟒 ∗ 𝟔

𝟔.𝟓 ∗𝟖.𝟓 = 43.4 kPa

cc = 0.009 (L.L. – 10)

→ cc = 0.009 (60 – 10) = 0.45

∆H = 𝒄𝒄

𝟏+𝒆 . H . Log

𝝈𝒐+∆𝝈

𝝈𝒐

Step (1): Determine the external stress

Step (2): Determine the Settlement

 Page :26 Dr. Eng. Mohamed Ezzat EM306: Soil Mechanics and Foundations

∆H = 𝟎.𝟒𝟓

𝟏+𝟏.𝟏 * 500 * log

𝟒𝟎.𝟓+𝟒𝟑.𝟒

𝟒𝟎.𝟓 = 20 cm

 Consolidation in Soil Topic No. 8

RECIPE FOR SUCCESS,

As long as you live, Just Keep

L e a r n i n g …

References

 Page :27 Dr. Eng. Mohamed Ezzat EM306: Soil Mechanics and Foundations

• Das, B., M. (2014), “ Principles of geotechnical Engineering ” Eighth Edition, CENGAGE Learning, ISBN-

13: 978-1-133-10867-2.

• Knappett, J. A. and Craig R. F. (2012), “ Craig’s Soil Mechanics” Eighth Edition, Spon Press, ISBN: 978-0-

415-56125-9.

• Orabi, A. (2015),Soil Mechanics, “Introduction &Properties of Soil lecture notes”, International university of

sciences and technology.

• Terzaghi, K. (1936) "Stress Distribution in Dry and in Saturated Sand Above a Yielding Trap-Door",

Proceedings. First International Conference on Soil Mechanics and Foundation Engineering, Cambridge,

Massachusetts, pp. 307-311.

• Terzaghi, K. (1943). “Theoretical Soil Mechanics”. John Wiley & Sons, New York.

• Meyerhof, G. G. (1951). “The Bearing Capacity of Foundations”. In Géotechnique, vol. 2, no. 4, pp. 301-

332.

• Radwan, A. (2013), “fundamentals of Soil Mechanics”. Helwan university, Faculty of engineering. Civil

Department library.

• El-Kadi, F. (2002), “Principles of Soil Mechanics”. Ain shams university, Faculty of engineering. Civil

Department library.

• Vesic, A. S. (1975). Principle of pile foundation design. Soil Mechanics Series No 38, School of

Engineering, Duke University.

• Joseph E. Bowels, (1999), "Physical and Geotechnical Properties of Soils"; McGraw Hill Book.

 Consolidation in Soil Topic No. 8

• Presentation of the theories and principles of soil mechanics

and foundation engineering.

• Explore the equipment's and instrumentations used for in-situ

and laboratory testing of soil.

• Outline the design standards of different types of foundation,

soil support systems according to several international codes.

• Provide sufficient field case studies and solved examples so that

students can make judgements as to the credibility of results

that they may obtain, or review, in the future.

Soil is a complex multiphase material. A sound understanding of

the fundamental principles and design applications of soil

mechanics is needed to predict the behavior and performance of

soil as a construction material or as a supporting medium for

engineering structures.

The main objective of this course is to provide the undergraduate

student with an insight into the theories and principles of soil

mechanics and foundation engineering, and its applications in

practical problems. The methodology that will be followed in this

course to achieve its objectives are directed towards the following

points:

Preface

Course Instructor

Dr. Mohamed Ezzat Al-Atroush

Dr. Mohamed Ezzat obtained his Ph.D. Degree from Ain Shams University, Egypt, in 2018. He joined the Prince Sultan University (PSU) in 2019 as an Assistant Professor in the area of Civil Engineering. He has broad experience in the field of geotechnical engineering on academic and professional works. Also, he has published many international journal and conference publications in the area of Geotechnical Engineering. He is a member of several international technical committees, such as the American society ofcivil engineers (ASCE).

On the other hand, Dr. Ezzat participated in many consultancy projects involving site investigations, problematic soils, evaluation of stability of slopes and escarpments, construction and permanent dewatering, design of deep excavation support, traditional and specialized lab testing, field monitoring, geophysical studies, foundation and bridge design, effect of tunnel induced ground deformations on adjacent surface and underground structures. His main research interests are in the Large Diameter bored piles, tunneling and deep excavations, Dynamic soil-structure interaction, Ground Improvement, and Energy and Sustainable Geotechnics.

Prince Sultan University, Riyadh, Saudi Arabia, 2019-2020