foundation engineering 5th lecture: bearing capacity cont’d · dr. hussein m. al.khuzaie;...
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FoundationEngineering5th Lecture:BearingCapacityCont’dScope:• ExampleonLocalShearFailure• DevelopmentofTerzaghi’sEquationbyHansen(shape,depth,andinclinationFactors)
• MeyerhofApproach• Comparisonbetweenallapproaches
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Hereβ inclinationoftheloadonthefoundationwithrespecttothevertical,
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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
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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.
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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.
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Bearing-capacity factors for the Meyerhof, bearing capacity equations
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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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usseinM
.Al.Khu
zaie;h
ma@
mu.ed
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Table of inclination, ground, and base factors for the Hansen equations.
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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.
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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.
Dr.HusseinM.Al.Khuzaie;[email protected]
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.
Dr.HusseinM.Al.Khuzaie;[email protected]
Dr.HusseinM.Al.Khuzaie;[email protected]