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 ï 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 ï less will be earth pressure
7. 8
ïłvâ(or ïłoâ)
ïłvâ
ïłhâïłhâ
Case â I
Rigid wall ï No movement
Earth pressure at rest
LATERAL EARTH PRESSURE â
CONCEPT
z
Pressure exerted on wall/structure with its lateral movement restrained
How to determine
Lateral Earth
Pressure
?
đŸ0 =
đâ
âČ
đđŁ
âČ
Coefficient of earth pressure at rest;
Using Earth Pressure Coefficients
8. 9
LATERAL EARTH PRESSURE â
CONCEPT
ïłv
ïłv
ïłh
Case â II
ï± Wall moving away from soil
ï± Active Earth pressure, Ka
ï± Ka << Ko
Ko
Kp
âPassive Stateâ
Failure due to compression
âAt Restâ - no strain
Ka
âActive Stateâ
Failure due to expansion
ï„Tension (-) Compression (+)
Earth Pressure
âActive Stateâ
Failure due to expansion/tension in soil
âPassive Stateâ
Failure due to compression
Case â III
ï± Wall moving towards soil
ï± Passive Earth pressure, Kp
ï± Kp >> Ko
12. 13
EARTH PRESSURE COEFFICIENT
AT REST (Ko)
Vertical effective stress = ïłâo = gz
Horizontal effective stress = ïłâh = Kogz
For loose coarse-grained soil, KO can be
estimated by using the empirical relationship
(Jacky, 1944)
where fâ = 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
đŸ0 = 1 â sin đâČ
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
đŸ0 = 1 â sin đâČ â (đđ¶đ )0.5
For OCC
21. 25
CONCLUDED
REFERENCE MATERIAL
Principles of Geotechnical Engineering â (7th Edition)
Braja M. Das
Chapter #13
Essentials of Soil Mechanics and Foundations (7th Edition)
David F. McCarthy
Chapter #17
Geotechnical Engineering â Principles and Practices â (2nd Edition)
Coduto, Yueng, and Kitch
Chapter #17