© Park 지반공학및실험 lecture_05_shallow_foundation_capacity

Lecture 5 Shallow Foundations Bearing Capacity

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Bearing Capacity: 3 regions

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Model test

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토질역학 Review - 전단강도

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토질역학 Review - 전단강도

Ultimate Bearing Capacity: The load per unit area of the foundation at whichshear failure in soil occurs (Resistance > Load)

Design Criteria: Settlement(Expected settlement < Tolerable settlement)

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© Park 지반공학및실험 lecture_05_shallow_foundation_capacity

Bearing Capacity Equation

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© Park 지반공학및실험 lecture_05_shallow_foundation_capacity

Bearing Capacity Equation

qu

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© Park 지반공학및실험 lecture_05_shallow_foundation_capacity

Bearing Capacity Equation

Lecture Outline

•Terzaghi’s Bearing Capacity Equation

•Modified Bearing Capacity Equation

•Shape, Depth, Inclination Factors

•Bearing Capacity in Clays (’=0)

•Bearing Capacity in Sands (c’=0)

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© Park 지반공학및실험 lecture_05_shallow_foundation_capacity

Terzaghi’s Bearing Capacity Theory

45-’/2

Shallow if Df ≤ B

A C

D EF

GH

IJ

3 Zones1. Triangular Zone: ACD2. Radial Shear Zone: ADF and CDE (DE and DF are arcs of a logarithmic spiral)3. Rankine Passive Zone: AFH and CEG

Another Assumption: = ’

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© Park 지반공학및실험 lecture_05_shallow_foundation_capacity

Terzaghi’s Bearing Capacity Theory

)(21' foundationstripBNqNNcq qcu

)(3.0'3.1 foundationcircularBNqNNcq qcu

)(4.0'3.1 foundationsquareBNqNNcq qcu

2(3 /4 '/2) tan '

2 '2cos 452

qeN

'cot1 qc NN

'tan1'cos2

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pK

N

Mathematically Exact Solutions

Non analytical solution

General shear failure mode

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© Park 지반공학및실험 lecture_05_shallow_foundation_capacity

Terzaghi’s Bearing Capacity Theory

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Modified Bearing Capacity EquationTerzaghi’s Assumption: = ’

New Assumption: = 45 + ’/2

'cot1 qc NN

'tan2

2'45tan eNq

N 2 Nq 1 tan ' Caquotand Kerisel (1953), Vesic(1973)

N Nq 1 tan 1.4 ' Meyerhof 1963 N 1.5 Nq 1 tan ' Hansen 1970

Mathematically Exact SolutionsNot analytical

solution

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Check page 139

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Nγ

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© Park 지반공학및실험 lecture_05_shallow_foundation_capacity

General Bearing Capacity Equation

idsqiqdqsqcicdcscu FFFBNFFFqNFFFNcq 21'

Shape FactorsFcs, Fqs, Fs

Depth FactorsFcd, Fqd, Fd

Inclination FactorsFci, Fqi, Fi

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Shape Factor

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Depth Factor

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Meyerhof (1963)’s factors

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Hansen (1970)’s factors

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Vesic (1973)’s factors

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Shape and Depth Factors

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