MatakuliahMatakuliah : S2094 / Rekayasa Pondasi: S2094 / Rekayasa Pondasi

TahunTahun : 2005: 2005

VersiVersi : 1.1: 1.1

Pertemuan 07Pertemuan 07Daya Dukung Pondasi DangkalDaya Dukung Pondasi Dangkal

Shallow FoundationsShallow Foundations

• Shallow Foundations versus Deep Shallow Foundations versus Deep FoundationsFoundations

Shallow FoundationsShallow Foundations

• Usually the more economical optionUsually the more economical option• As a general rule, consider deep As a general rule, consider deep

foundations only when shallow foundations only when shallow foundations do not give satisfactory foundations do not give satisfactory designdesign

• Types of Shallow foundationsTypes of Shallow foundations• Spread footings (square, circular, Spread footings (square, circular,

rectangular)rectangular)• Combined FootingsCombined Footings• Continuous Footings Continuous Footings • Mat or Raft Foundations Mat or Raft Foundations

Combined/Strap FootingCombined/Strap Footing

Construction MethodsConstruction Methods

• Excavation; Backhoe followed by Excavation; Backhoe followed by handworkhandworko Neat footing-no formwork usedNeat footing-no formwork usedo Formed footingFormed footing

Mat (or Raft) FoundationMat (or Raft) Foundation

Computation of Bearing Computation of Bearing PressurePressure

Bearing PressureBearing Pressure– Gross Bearing Pressure (q)Gross Bearing Pressure (q)– Net Bearing Pressure(qNet Bearing Pressure(q´)´)

Bearing CapacityBearing Capacity– Ultimate Bearing Capacity (qUltimate Bearing Capacity (qultult))

– Allowable Bearing Capacity (qAllowable Bearing Capacity (qa)a)

Computation of Bearing Computation of Bearing PressurePressure

Column Load (Ex 5.1)Column Load (Ex 5.1)

Wall Load (Ex 5.2)Wall Load (Ex 5.2)D

f uA

WPq

D

f

uB

bW

bP

q

Net Bearing PressureNet Bearing PressureNet Bearing Pressure (qNet Bearing Pressure (q´) ´)

Floating FoundationFloating Foundation– When qWhen q´ = 0´ = 0– ExampleExample: Student Center Building at MIT: Student Center Building at MIT

Estimated without floatation settlement = 1.0ft Estimated without floatation settlement = 1.0ft and settlement with partial floatation was 2-3 and settlement with partial floatation was 2-3 inchesinches

zoqq

Eccentric Loads or MomentsEccentric Loads or Moments

Eccentric Loads or MomentsEccentric Loads or Moments

Eccentric Loads or MomentsEccentric Loads or Moments

B

eu

A

WPq D

f 61min

B

eu

A

WPq D

f 61max

Two-way Eccentric Loads or Two-way Eccentric Loads or MomentsMoments

Eccentric Loads or MomentsEccentric Loads or Moments

L

e

B

eu

A

WPq LB

Df 661

For contact pressure to remain (+) ve everywhere,

0.166

L

e

B

e LB