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.
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
12. 13
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′
13. 14
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
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