project class
osama
T.9_SoilShearStrength.pdf
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)
Soil Shear Strength
Topic No. 9
Topic (9)
❑ 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
❑ Soil Shear Strength Topic No. 9
SHEAR STRENGTH OF SOIL
❑ Soil Shear Strength Topic No. 9
❑ Page :2 Dr. Eng. Mohamed Ezzat EM306: Soil Mechanics and Foundations
1. DEFINITION:
When a soil is subjected to vertical and lateral stresses, deformations in different directions may occur. The pore water pressure and water content of the soil may also change. When the stress exceeds a certain limit, accompanied by a certain strain, failure of the soil occurs. This failure is usually characterized by movement of the affected soil mass by slip along a certain plane, which is called the shear plane.
❑ Soil Shear Strength Topic No. 9
❑ Page :3 Dr. Eng. Mohamed Ezzat EM306: Soil Mechanics and Foundations
2. THE MOHR-COULOMB FAILURE CRITERION
τf = c + σ tan ɸ
Where
τf : Shear strength of the soil σ: Normal stress acting on the plane of failure c, ɸ: Shear strength parameters c: Apparent cohesion ɸ: Angle of shear resistance (internal friction)
As a function of effective normal stress:
τf = c' + σ tan ɸ'
c', ɸ': Effective shear strength parameters.
Where
❑ Soil Shear Strength Topic No. 9
❑ Page :4 Dr. Eng. Mohamed Ezzat EM306: Soil Mechanics and Foundations
❑ Soil Shear Strength Topic No. 9
❑ Page :5 Dr. Eng. Mohamed Ezzat EM306: Soil Mechanics and Foundations
4. DETERMINATION OF SHEAR STRENGTH PARAMETERS (a) Direct shear test
❑ Soil Shear Strength Topic No. 9
❑ Page :6 Dr. Eng. Mohamed Ezzat EM306: Soil Mechanics and Foundations
4. DETERMINATION OF SHEAR STRENGTH PARAMETERS (a) Direct shear test
Three types of the test can be carried out:
1. Slow test: Pore water pressure will not developed during test. 2. Consolidated–quick test: Sample is allowed to consolidate under the vertical load,
followed by quick shear. 3. Quick test: Water content of the sample remains unchanged during test.
Disadvantages of shear box:
❑ Shear stresses are unequally distributed over the shear surface. ❑ Area of shear surface changes as test progresses. ❑ Water content of saturated samples of many types of soil may be changed.
❑ Soil Shear Strength Topic No. 9
❑ Page :7 Dr. Eng. Mohamed Ezzat EM306: Soil Mechanics and Foundations
For loose sand and gravel, the cohesion (c) is equal to zero.
τ = σ tan ɸd
Angle of repose
❑ Soil Shear Strength Topic No. 9
❑ Page :8 Dr. Eng. Mohamed Ezzat EM306: Soil Mechanics and Foundations
1. The soil at a site is formed of sand. The groundwater is 2 m below ground surface. The angle of internal friction of the sand is 35o, its dry density is 1.8 t/m3 and specific gravity 2.65. Find the shear resistance of the soil at a depth of 5 m.
Example 1
❑ Soil Shear Strength Topic No. 9
❑ Page :9 Dr. Eng. Mohamed Ezzat EM306: Soil Mechanics and Foundations
γd = 𝑮𝒔
𝟏+𝒆 . γw 1.80 =
2.65
1+𝑒 * 1.00
e = 0.472
γsat = 𝑮𝒔+𝒆
𝟏+𝒆 . γw =
2.65+0.472
1+0.472 = 2.12 t/m3
σ = γd . H1 + γsat . H2 = 1.80 * 2.00 + 2.12 * 3.00 = 9.96 t/m2
u = γw . Hw = 1.00 * 3.00 = 3.00 t/m 2
σ' = σ - u = 9.96 – 3.00 = 6.96 t/m2
τf = c + σ tan f = zero + 6.96 tan 35 = 4.88 t/m 2
Solution:
❑ Soil Shear Strength Topic No. 9
❑ Page :10 Dr. Eng. Mohamed Ezzat EM306: Soil Mechanics and Foundations
2. A direct shear box test was carried out on dry coarse sand. The box is 6 x 6 cm. When a normal load of 28.8 kg was applied, the shear load at failure was 17.3 kg. find the angle of internal friction of the sand. Find the magnitude and direction of the principal stresses.
Example 2
❑ Soil Shear Strength Topic No. 9
❑ Page :11 Dr. Eng. Mohamed Ezzat EM306: Soil Mechanics and Foundations
σ = 𝑵𝒐𝒓𝒎𝒂𝒍 𝒍𝒐𝒂𝒅
𝑨𝒓𝒆𝒂 = 28.80
6 ∗6 = 0.80 kg/cm2
τ = 𝑺𝒉𝒆𝒂𝒓 𝒍𝒐𝒂𝒅
𝑨𝒓𝒆𝒂 = 17.30
6 ∗6 = 0.48 kg/cm2
Draw σ – τ Plot point A (0.80 , 0.48)
Plot OA, this is the rupture line ϕ = 31o
Draw AM ┴ OA, M is the center of Mohr circle
σ3 = OB = 0.528 kg/cm 2 & σ1 = OC = 1.648
Solution:
❑ Soil Shear Strength Topic No. 9
❑ Page :12 Dr. Eng. Mohamed Ezzat EM306: Soil Mechanics and Foundations
3. Quick shear box tests were carried out on three specimens of partially saturated clay. Results are as follows:
Find the apparent cohesion and angle of internal friction. Determine the unconfined compressive strength of a specimen of the same soil.
Example 3
❑ Soil Shear Strength Topic No. 9
❑ Page :13 Dr. Eng. Mohamed Ezzat EM306: Soil Mechanics and Foundations
Draw AM ┴ rupter line, M is the center of Mohr circle
Draw σ – τ , Draw rupture line Measure ϕ = 8.60o & cu = 0.8 kg/cm
2
To draw Mohr circle with σ3 = zero
Calculate α = 45 + ϕ
𝟐 = 45 +
8.60
2 = 49.3o
Draw OA making an angle α to the horizontal
qun = σ1 = 1.88 kg/cm 2
Solution:
❑ Soil Shear Strength Topic No. 9
❑ Page :14 Dr. Eng. Mohamed Ezzat EM306: Soil Mechanics and Foundations
4. Quick shear box tests were carried out on three specimens of sandy clay. The cross section of the shear box was 6 x 6 cm. Results are as follows:
If a specimen of the same soil is tested in triaxial compression with cell pressure of σ3 = 1 kg/cm 2,
find the total axial stress at which failure will be expected to occur.
Example 4
❑ Soil Shear Strength Topic No. 9
❑ Page :15 Dr. Eng. Mohamed Ezzat EM306: Soil Mechanics and Foundations
divide results by the area of the shear box (6 * 6 cm)
Plot the results, Measure ϕu = 14 o & cu = 0.44 kg/cm
2
To draw Mohr circle with σ3 = 1.00
From A, Draw AM ┴ rupture line
M is the center of Mohr circle, σ1 = 2.77 kg/cm 2
Calculate α = 45 + ϕ
𝟐 = 45 +
𝟏𝟒
2 = 52o
Draw BA making an angle α to the horizontal
Solution:
❑ Soil Shear Strength Topic No. 9
❑ Page :16 Dr. Eng. Mohamed Ezzat EM306: Soil Mechanics and Foundations
4. DETERMINATION OF SHEAR STRENGTH PARAMETERS
(b) Triaxial compression test
❑ Soil Shear Strength Topic No. 9
❑ Page :17 Dr. Eng. Mohamed Ezzat EM306: Soil Mechanics and Foundations
4. DETERMINATION OF SHEAR STRENGTH PARAMETERS Three types of the test can be carried out:
1. 1. Quick (unconsolidated–undrained) UU-test: No drainage is allowed. 2. Consolidated–quick (consolidated–undrained) CU-test: Drainage is allowed in the
consolidation stage only. 3. Slow (consolidated–drained) CD-test: Drainage is allowed in all stage of the test.
❑ Soil Shear Strength Topic No. 9
❑ Page :18 Dr. Eng. Mohamed Ezzat EM306: Soil Mechanics and Foundations
5. The results of consolidated undrained triaxial tests with pore water pressure measurement on a compacted soil at failure are as follows:
Determine the apparent cohesion and angle of internal friction referred to total and effective stresses.
Example 5
❑ Soil Shear Strength Topic No. 9
❑ Page :19 Dr. Eng. Mohamed Ezzat EM306: Soil Mechanics and Foundations
For total stress analysis
For effective stress analysis
Solution:
❑ Soil Shear Strength Topic No. 9
❑ Page :20 Dr. Eng. Mohamed Ezzat EM306: Soil Mechanics and Foundations
4. DETERMINATION OF SHEAR STRENGTH PARAMETERS
(c) Unconfined compressive strength test
❑ Soil Shear Strength Topic No. 9
❑ Page :21 Dr. Eng. Mohamed Ezzat EM306: Soil Mechanics and Foundations
(d) Pocket penetrometer test
4. DETERMINATION OF SHEAR STRENGTH PARAMETERS
It can be used for ordinary works, the unconfined compressive strength can be measured directly
❑ Soil Shear Strength Topic No. 9
❑ Page :22 Dr. Eng. Mohamed Ezzat EM306: Soil Mechanics and Foundations
(e) Vane shear test
4. DETERMINATION OF SHEAR STRENGTH PARAMETERS
❑ The test is suitable for saturated clays of very soft to firm consistency.
❑ Field vane tests are typically 50–75 mm diameter and 100 –150 mm long.
❑ Laboratory vanes, 13 mm diameter and 50 mm long.
Torque = D2 cu ( 𝑯
𝟐 +
𝐷
6 )
cu (field) = . cu
❑ Soil Shear Strength Topic No. 9
❑ Page :23 Dr. Eng. Mohamed Ezzat EM306: Soil Mechanics and Foundations
6. A vane 10 cm long and 8 cm diameter was used to measure the shear strength of a soft clay. The torque at failure was 450 kg.cm. Calculate the undrained cohesion.
Torque = D2 cu ( 𝑯
𝟐 +
𝐷
6 )
450 = (8)2 cu ( 𝟏𝟎
𝟐 +
8
6 )
cu = 0.35 kg/cm 2
Solution:
Example 6
❑ Soil Shear Strength Topic No. 9
❑ Page :24 Dr. Eng. Mohamed Ezzat EM306: Soil Mechanics and Foundations
RECIPE FOR SUCCESS,
As long as you live, Just Keep
L e a r n i n g …
References
❑ Page :25 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.
❑ Soil Shear Strength Topic No. 9
• 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
