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.

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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 # 13
18-Oct-2017

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Practice Problem #2
Bore holes at a building site show the following strata (levels in meters
measured from ground surface)
Top Soil 0 to -1
Sand -1 to -5 (Water table at -3.5)
Clay -5 to -9
There is impervious rock below -9 m. The bulk density of the top soil and
sand is 19.62 kN/m3 and that of clay is 18.83 kN/m3.
A building is constructed on a concrete raft 324 m2 at 3 m below the surface.
The total load is 90x103 kN. Assuming a spread of the load of 2 vertical to 1
horizontal, calculate the final settlement. The coefficient of volume
compressibility (mV) is 434x10-6 m2/kN.
In a consolidation test, a specimen of the clay reached 90% settlement in 4
hours. The specimen was 20 mm thick. Estimate the time in years for the
building to reach 90% of its final settlement.

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MAGNITUDE OF SETTLEMENT
CALCULATION
Consolidation Settlement
Today’s Discussion

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• Caused by elastic
deformation of
dry/moist/saturated soil
• No change in moisture
content i.e. “Undrained
Settlement”
• Occurs immediately
after the construction
• Important for Granular
soil
IMMEDIATE (ELASTIC) SETTLEMENT

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Main parameters for elastic settlement computation
• Modulus of elasticity (Es)
• Poisson’s ratio (ν)
Determination of Elastic Parameters
• Laboratory tests  expensive, time consuming
• In-situ tests  expensive, reliability?
• Commonly determined through empirical correlations
• Use of empirical correlations depend upon limitations of
correlations, experience, engineering judgement, etc.
ELASTIC PARAMETERS

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POISSON’S RATIO
Found. Analysis & Design
Bowles (5th ed.)

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MODULUS OF ELASTICITY
Found. Analysis & Design
Bowles (5th ed.)

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MODULUS OF ELASTICITY
Found. Analysis & Design
Bowles (5th ed.)

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1. Methods Based Upon Theory of Elasticity
a. Timoshenko and Goodier (1951)
b. Mayne & Poulos (1999) Method
2. Methods Based Upon Strain Influence Factor
a. Schmertmann (1978) Method
b. Terzaghi et al. (1996) Method
3. Methods Based Upon SPT-N Values
a. Modified Mayerhof (1996) Method
b. Peck and Bazaraa Method
c. Burland and Burbridge (1985) Method
4. Elastic Settlement of Saturated Clays
a. Janbu, Bjerrum, and Kjaernsli (1956) Method
IMMEDIATE (ELASTIC) SETTLEMENT
COMPUTATION
Mainly
SANDS

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ASSUMPTIONS
• Strictly applicable to flexible bases on half-space.
• The half-space may either be cohesionless materials of any
water content or unsaturated cohesive soils.
• The soils may either be inorganic or organic; however, if
organic, the amount of organic material should be small,
because both Es and s are markedly affected by high organic
content.
• In practice, most foundations are flexible. Even very thick
ones deflect when loaded by the superstructure loads.
• If the base is rigid, the settlement will be uniform, and the
settlement factor IS will be about 7 % less than computed by
equations. If footing base is considered rigid, ISR = 0.931IS
TIMOSHENKO AND GOODIER (1951)
METHOD

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Settlement at the corner of uniformly loaded flexible rectangular
footing of dimensions B’xL’ from Timoshenko and Goodier
(1951) is given as;
TIMOSHENKO AND GOODIER (1951)
METHOD
Found. Analysis & Design
Bowles (5th ed.) P-303

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IF
Square foundation; L/B = 1
Strip foundation; L/B ≥ 5

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Settlement at the corner of uniformly loaded flexible rectangular
footing of dimensions B’xL’ from Timoshenko and Goodier
(1951) is given as;
TIMOSHENKO AND GOODIER (1951)
METHOD
Found. Analysis & Design
Bowles (5th ed.) P-303

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TIMOSHENKO AND GOODIER (1951)
METHOD Found. Analysis & Design
Bowles (5th ed.) P-303
H = thickness of compressible layer

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ADD a Slide for description of
Es i.e. Hard layer for next
year.
Use Bowles & Das for reference.
Also for Round Bases, Convert into Equivalent
Square
TIMOSHENKO AND GOODIER (1951)
METHOD

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PRACTICE PROBLEM #3
Estimate the elastic settlement at the center of the raft (or mat)
foundation for a building with the given data;
qo = 134 kPa; B x L = 33.5 x 39.5 m
The strata comprises of a 6.0 m thick dense sand deposit (ES =
42.5 MPa) overlying a hard clay stratum (ES = 60 MPa)
extending to a depth of 14.0 m below NSL. A sandstone deposit
(ES ≥ 500 MPa) exists below 14.0 m depth. The foundation is
placed at a depth of 3.0 m below NSL.

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IF
Square foundation; L/B = 1
Strip foundation; L/B ≥ 5

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PRACTICE PROBLEM #4

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IF
Square foundation; L/B = 1
Strip foundation; L/B ≥ 5

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CONCLUDED
REFERENCE MATERIAL
Foundation Analysis and Design (5th Ed.)
Joseph E. Bowles
Chapter #5
Principles of Geotechnical Engineering (7th Ed.)
Braja M. Das
Chapter #11
Essentials of Soil Mechanics and Foundations (7th Ed.)
David F. McCarthy
Chapter #10
(Schmertmann Method)
(Timoshenko & Goodier Method)
(Modified Mayerhof Method)