Class notes of Geotechnical Engineering course I used to teach at UET Lahore. Feel free to download the slide show. Anyone looking to modify these files and use them for their own teaching purposes can contact me directly to get hold of editable version.

1. 1
Geotechnical Engineering–II [CE-321]
BSc Civil Engineering – 5th Semester
by
Dr. Muhammad Irfan
Assistant Professor
Civil Engg. Dept. – UET Lahore
Email: mirfan1@msn.com
Lecture Handouts: https://groups.google.com/d/forum/geotech-ii_2015session
Lecture # 21
22-Nov-2017

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EARTH PRESSURE
Pressure exerted by soil on structures.

3. 3
EARTH PRESSURE
Pressure exerted by soil on structures.
Wall moving
towards soil

4. 4
EARTH PRESSURE – SIGNIFICANCE
Purpose of this wall?
Main load acting on
wall?
-- Earth pressure
How to determine it?

5. 5
EARTH PRESSURE – SIGNIFICANCE

6. 6
WHAT AFFECTS EARTH
PRESSURE?
-- Soil type
Strong soil  less pressure
(e.g. OCC soil will have less EP)
-- Imposed loading
- Self weight of soil (overburden)
- Surcharge load
-- Soil-structure interaction
More the soil-structure friction  less will be earth pressure

7. 8
v’(or o’)
v’
h’h’
Case – I
Rigid wall  No movement
Earth pressure at rest
LATERAL EARTH PRESSURE –
CONCEPT
z
Pressure exerted on wall/structure with its lateral movement restrained
How to determine
Lateral Earth
Pressure
?
𝐾0 =
𝜎ℎ
′
𝜎𝑣
′
Coefficient of earth pressure at rest;
Using Earth Pressure Coefficients

8. 9
LATERAL EARTH PRESSURE –
CONCEPT
v
v
h
Case – II
 Wall moving away from soil
 Active Earth pressure, Ka
 Ka << Ko
Ko
Kp
“Passive State”
Failure due to compression
“At Rest” - no strain
Ka
“Active State”
Failure due to expansion
Tension (-) Compression (+)
Earth Pressure
“Active State”
Failure due to expansion/tension in soil
“Passive State”
Failure due to compression
Case – III
 Wall moving towards soil
 Passive Earth pressure, Kp
 Kp >> Ko

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EARTH PRESSURE
-- REAL LIFE SCENARIO --

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LATERAL EARTH PRESSURE –
CONCEPT
Typical Values

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WALL MOVEMENT TO ACTIVATE
ACTIVE/PASSIVE EARTH PRESSURE

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EARTH PRESSURE COEFFICIENT
AT REST (Ko)
Vertical effective stress = ’o = gz
Horizontal effective stress = ’h = Kogz
For loose coarse-grained soil, KO can be
estimated by using the empirical relationship
(Jacky, 1944)
where f’ = drained friction angle
For dense sand backfill, Jacky formula may
underestimate the effect of compaction and thus
KO. The following formula should be used
gd = actual compacted unit wt. of the sand behind the
wall
gd(min) = dry unit wt. of sand in the loosest state
𝐾0 = 1 − sin 𝜙′

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EARTH PRESSURE COEFFICIENT
AT REST (Ko)
The increase of Ko in dense sands compared to
Jacky formula is due to over-consolidation.
For fine grained, normally consolidated soils
𝐾0 = 1 − sin 𝜙′ ∙ (𝑂𝐶𝑅)0.5
For OCC

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EARTH PRESSURE COEFFICIENT AT
REST (Ko)

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EARTH PRESSURE ON A WALL AT
REST

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EARTH PRESSURE ON A WALL AT
REST
Partially Submerged Soil
gsub (or g’) = gsat - gw

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EARTH PRESSURE ON A WALL AT
REST
Partially Submerged Soil

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EARTH PRESSURE ON A WALL AT
REST Partially Submerged Soil
Force per unit length of the wall
= Sum of areas of pressure diagram

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Practice Problem #1

20. 24
LATERAL EARTH PRESSURE – Review

21. 25
CONCLUDED
REFERENCE MATERIAL
Principles of Geotechnical Engineering – (7th Edition)
Braja M. Das
Chapter #13
Essentials of Soil Mechanics and Foundations (7th Edition)
David F. McCarthy
Chapter #17
Geotechnical Engineering – Principles and Practices – (2nd Edition)
Coduto, Yueng, and Kitch
Chapter #17