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)

Bearing Capacity and Shallow Foundations

Topic No. 10

Topic (10)

❑ 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

❑ Bearing Capacity and Shallow Foundations Topic No. 10

The Design of foundations have to satisfy Two fundamental requirements, respectively;

Fig (2), Relative and total settlement of pisa tower.

1. Complete failure of the foundation must be prevented with an sufficient margin of safety.

2. The relative and total settlements of the foundation must be kept within limits that can be tolerated by the superstructure.

Fig (1), Foundation Failure of the condo building in

China

PRINCIPLE OF FOUNDATION DESIGN

(Meyerhof, 1951)

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

❑ Bearing Capacity and Shallow Foundations Topic No. 10

1. Safety factor of two is generally used in practice to obtain the maximum safe foundation load (Load Control Criteria).

2. The settlement of the foundation under working load has to be estimated independently to ascertain its effect on the superstructure (Settlement Control Criteria).

PRINCIPLE OF FOUNDATION DESIGN

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

❑ Bearing Capacity and Shallow Foundations Topic No. 10

INTRODUCTION ❑ Foundations may be classified as

o Shallow (e.g. isolated footing, raft foundation) Df≤ 4.0 m o Deep (pier, drilled shaft, or pile group) Df 4.0 m

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

❑ Bearing Capacity and Shallow Foundations Topic No. 10

❑ Footing may be classified in several ways o Individual footing o Combined footing o Wall footing o Strap footing o Mat or raft foundation

TYPES OF SHALLOW FOUNDATIONS

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

❑ Bearing Capacity and Shallow Foundations Topic No. 10

❑ Foundations must be designed to satisfy Three general criteria 1. They must be located properly so as not to be adversely affected by outside

influence 2. They must be safe from bearing capacity failure 3. They must be safe from excessive settlement

FOUNDATION DESIGN

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

❑ Bearing Capacity and Shallow Foundations Topic No. 10

❑ In general the typical load/pressure types includes: o Dead load o Live load o Wind load o Snow load o Earth pressure o Water pressure o Earthquake forces

LOADS ON FOUNDATIONS

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

❑ Bearing Capacity and Shallow Foundations Topic No. 10

❑ The depth & location of foundations are dependent on : o Significant soil volume change o Adjacent structures & property lines o Groundwater o Underground defects o Building codes

DEPTH & LOCATION OF FOUNDATIONS

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

❑ Bearing Capacity and Shallow Foundations Topic No. 10

❑ Bearing capacity: refers to the ability of the soil to support a foundation & structure.

❑ Ultimate bearing capacity (qult): refers to the loading per unit area (Stress) that will just cause shear failure in the soil.

❑ Allowable bearing capacity (qa): refers to the loading per unit area that the soil is able to support without unsafe movement

BEARING CAPACITY ANALYSIS

qa = 𝒒𝒖𝒍𝒕

𝒇𝒂𝒄𝒕𝒐𝒓 𝒐𝒇 𝒔𝒂𝒇𝒆𝒕𝒚 (𝑭𝑶𝑺)

❑ A factor of safety (FOS) of 2.5 to 3.0 is commonly applied

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

❑ Bearing Capacity and Shallow Foundations Topic No. 10

THEORY OF BEARING CAPACITY

❑ The set of slip surface giving the least value of Q is the most critical

❑ As load (Q) is applied, the footing undergoes a certain amount of settlement as it is pushed downward ❑ A wedge of soil directly below the footing’s base move downward with the footing ❑ This is resisted by shear resistance of the soil along the slip surfaces cde & cfg (see Fig. 9.6) & weight of the soil in sliding

wedge acfg & bcde

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

❑ Bearing Capacity and Shallow Foundations Topic No. 10

❑ The following equations for calculating qult were developed by Terzaghi (Terzaghi and Peck, 1967)

BEARING CAPACITY ANALYSIS

❑ Continuous footing (width B)

qult = cNc + γ1 Df Nq + 0.5 γ2 BNγ eqn 9.1

Where, qult = ultimate bearing capacity c = cohesion Nc , Nq , Nγ = Terzaghi’s bearing capacity factors γ1 = effective unit weight of soil above base of foundation γ2 = effective unit weight of soil below foundation Df = depth of footing or distance from ground surface to base of footing B = width of continuous or square footing R = radius of circular footing

for both cohesive & cohesionless soils

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

❑ Bearing Capacity and Shallow Foundations Topic No. 10

❑ Circular footing (radius R)

qult = 1.2 cNc + γ1 Df Nq + 0.6 γ2 RNγ eqn 9.2

❑ Square footing (Width B)

qult = 1.2 cNc + γ1 Df Nq + 0.4 γ2 BNγ eqn 9.3

BEARING CAPACITY ANALYSIS for both cohesive & cohesionless soils

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

❑ Bearing Capacity and Shallow Foundations Topic No. 10

❑ Values of Terzaghi’s dimensionless bearing capacity factors for different values of  can be obtained from Fig. 9.7 or Table 9.1 or equations below:

BEARING CAPACITY ANALYSIS

Nq = e  tanϕ tan2 𝟒𝟓𝒐 +

ϕ

𝟐 eqn 9.4

Nc = cot ϕ (Nq – 1) eqn 9.5

Nγ = (Nq – 1) tan (1.4 ϕ) eqn 9.6

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

❑ Bearing Capacity and Shallow Foundations Topic No. 10

❑ Dense sand & stiff clay produce what is called general shear

❑ Loose sand & soft clay produce local shear ❑ For the latter, Nc, Nq & N are replaced by N’c, N’q

& N’

TYPES OF FAILURE

c’ = 𝟐

𝟑 c eqn 9.7

ϕ’ = arctan ( 𝟐

𝟑 tan ϕ) eqn 9.8

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

❑ Bearing Capacity and Shallow Foundations Topic No. 10

❑ In the case of cohesionless soils, c = 0

❑ Value of  may be determined using corrected SPT values as covered in Chapter 3 or using this figure.

BEARING CAPACITY ANALYSIS ❑ For cohesive soils, shear strength is most critical just after

construction when shear strength is assumed to consist only of c

qult = cNc + γ1 Df Nq + 0.5 γ2 BNγ eqn 9.1

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

❑ Bearing Capacity and Shallow Foundations Topic No. 10

o qu = 134 kN/m2 o  = 20.40 kN/m3 o Groundwater was not encountered during

subsurface exploration o Df = 0.6m

❑ Determine the qult & allowable wall load using a FOS of 3

A strip of footing 1 m wide is supported in a uniform deposit of stiff clay. Given the following:

Example 1

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

❑ Bearing Capacity and Shallow Foundations Topic No. 10

❑ As the supporting stratum is stiff clay, a general shear condition is evident.

For a continuous wall footing

qult = cNc + γ1 Df Nq + 0.5 γ2 BNγ

= 134

2 = 67 kN/m2c =

𝒒𝒖

𝟐

γ1 = γ2 = 20.40 kN/m 3

Df = 0.6 m

B = 1 m

If we use c > 0 , ϕ = 0 analysis for cohesive soil, using the table, bearing capacity values are : Nc = 5.14, Nq = 1.0 , Nγ = 0

Solution:

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

❑ Bearing Capacity and Shallow Foundations Topic No. 10

(cont’d)

qult = (67) (5.14) + (20.40) (0.6) (1.0) + (20.40) (1) (0)

= 357 kN/m2

qa = (357)/3 = 119 kN/m 2

Allowable wall loading = qa * B

= (119) (1) = 119 kN/m of wall length

qult = cNc + γ1 Df Nq + 0.5 γ2 BNγ

qa = 𝒒𝒖𝒍𝒕

𝒇𝒂𝒄𝒕𝒐𝒓 𝒐𝒇 𝒔𝒂𝒇𝒆𝒕𝒚 (𝑭𝑶𝑺)

Solution:

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

❑ Bearing Capacity and Shallow Foundations Topic No. 10

A column footing 2 m x 2 m is buried 1.5 m below the ground surface in a dense cohesionless soil. The footing is to carry a total load of 1500 kN .The results of lab & field tests are as follows:

o  = 20.10 kN/m3 o Average corrected SPT N-value = 30 o Groundwater was not encountered during

subsurface exploration

❑ Determine the FOS against bearing capacity failure

Example 2

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

❑ Bearing Capacity and Shallow Foundations Topic No. 10

Because the supporting stratum is dense cohesionless soil, a general shear condition is evident.

qult = 1.2 cNc + γ1 Df Nq + 0.4 γ2 BNγ

c = 0

γ1 = γ2 = 20.10 kN/m 3

Df = 1.5 m

B = 2 m

From the chart, with Ncorrected = 30, ϕ = 36 o

the following bearing capacity factors are obtained:

Nq = 37.75 , Nγ = 44.43

Square Footing

Step (1): Find soil bearing capacity:

Solution:

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

❑ Bearing Capacity and Shallow Foundations Topic No. 10

qult = (1.2) (0) (Nc) + (20.10) (1.5) (37.75) + (0.4) (20.10) (2) (44.43)

qult = 1852.6 kN/m 2

qult = 1.2 cNc + γ1 Df Nq + 0.4 γ2 BNγ

qactual = 𝑸

𝑨 =

1500

2 ∗2 = 375 kN/m2

FOS against bearing capacity failure

FOS= 𝒒𝒖𝒍𝒕

𝒒𝒂𝒄𝒕𝒖𝒂𝒍 =

1852.6

375 = 4.9 > 3.0

Step (1): Find soil bearing capacity:

Step (2): Find Actual stress on the footing :

Step (3): Find FOS:

SAFE

Solution:

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

❑ Bearing Capacity and Shallow Foundations Topic No. 10

RECIPE FOR SUCCESS,

As long as you live, Just Keep

L e a r n i n g …

References

• 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.

❑ Page :59 Dr. Eng. Mohamed Ezzat EM306: Soil Mechanics and Foundations

❑ Bearing Capacity and Shallow Foundations Topic No. 10

• 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 of civil 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