Foundation Engineering 5th Lecture: Bearing Capacity Cont’d · Dr. Hussein M. Al.Khuzaie; [email protected] 20 Which Equations to Use ØThe Terzaghi equations, being the first proposed,

FoundationEngineering5th Lecture:BearingCapacityCont’dScope:• ExampleonLocalShearFailure• DevelopmentofTerzaghi’sEquationbyHansen(shape,depth,andinclinationFactors)

• MeyerhofApproach• Comparisonbetweenallapproaches

Dr.HusseinM.Al.Khuzaie;[email protected] 1






DepthfactorasbelowforDf /B ≤ 1


DepthfactorasbelowforDf /B ≥ 1

tan -1(Df /B) in RadianDr.HusseinM.Al.Khuzaie;[email protected] 8

Hereβ inclinationoftheloadonthefoundationwithrespecttothevertical,


Dr.HusseinM.Al.Khuzaie;[email protected]


For Cohesive Soil and for undrained condition of soil :f = 0Nc = 5.7; Nq =1.0; Ng = 0

qalln = { (c 𝑁" + q 𝑁$ + 0.5 B g 𝑁%) - q}/FS

=0=q

=c 𝑁"/FS

=qunc/2 ∗ (5.7/3

=qunc ∗ (~44) =qunc


Comparison between Terzaghi’s and Hansen with Meyerhof

Up to a depth ofD/ B in this Fig,

the Meyerhof qult is not greatly

different from theTerzaghi value. The difference becomes more pronounced at larger D/B ratios.


Meyerhof (1963).* *These methods require a trial process to obtain design base dimensions since width B andlength L are needed to compute shape, depth, and influence factors.



Bearing-capacity factors for the Meyerhof, bearing capacity equations


Hansen's Bearing-Capacity Method


Shape and depth factors for use in Hansen bearing-capacity equations, Use s'c , d'c when f = 0 only for Hansen equations.

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Table of inclination, ground, and base factors for the Hansen equations.



Which Equations to Use

Ø The Terzaghi equations, being the first proposed, have been very widely used.

Ø Their greater ease of use (one does not need to compute all the extra shape, depth, and other factors).

Ø They are only suitable for a concentrically loaded footing on horizontal ground.

Ø They are not applicable for footings carrying a horizontal shear and/or a moment or for tilted bases.

Ø Both the Meyerhof and Hansen methods are widely used.


Use Best forTerzaghi Very cohesive soils where D/B £1 or for a quick

estimate of quit to compare with other methods. Do not use for footings with moments and/or horizontal forces or for tilted bases and/or sloping ground.

Hansen and Meyerhof

Any situation that applies, depending on userpreference or familiarity with a particular method.

Hansen When base is tilted; when footing is on a slope or when D/B > 1.

§ It is good practice to use at least two methods and compare the computed values of qult.

§ If the two values do not compare well, use a third method.


Example :A footing load test in Berlin produced the following data:

Required:Compute the ultimate bearing capacity by both Hansen and Meyerhof

equations and compare these values with the measured value.



Documents

Foundation Engineering 5th Lecture: Bearing Capacity Cont’d · Dr. Hussein M. Al.Khuzaie; [email protected] 20 Which Equations to Use ØThe Terzaghi equations, being the first proposed,