04 Kuliah 2 2

LECTURE 2_2Soil compaction

Main reference

R.F. Craig , “ Soil Mechanics” 7th ed, 2004; Holtz, R.D. and Kovacs, W.D. (1981). An Introduction to

Geotechnical Engineering, Prentice Hall. Bowles, J.E., “Physical and Geotechnical Properties of

Soils”, McGraw-Hill Kogagusha Ltd., 1979. Braja M.Das, “Principles of Geotechnical Engineering”,

Fifth edition, 2004, PWS Publishing Company, Boston Budu M., “Soil Mechanics and Foundations”, Second

Edition, 2007, John Wiley& Sons, New York

Outline course 2

1. Soil texture2. Grain size distribution

1. Sieve analysis2. Hidrometer

3. Soil classification4. Atterberg limit

1. Liquid lilmit2. Plastic limit3. Shrinkage limit

5. Compaction 6. California Bearing Ratio (CBR)

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What is compaction?

A simple ground improvement technique, where the soil is densified through external compactive effort.

+ water =

Compactive effort

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Laboratory Compaction Test

- to obtain the compaction curve and define the optimum water content and maximum dry density for a specific compactive effort.

hammerStandard Proctor: Modified Proctor:

• 3 layers

• 25 blows per layer• 5 layers

• 25 blows per layer• 2.7 kg hammer

• 300 mm drop• 4.9 kg hammer

• 450 mm drop

1000 ml compaction mould

Compactive effort

Notation Standard Proctor

Modified Proctor

Weight hammer W 5,5 lb 10 lb

Falling height H 12” ( 1 ft ) 18” (1,5 ft )

Layer L 3 lapis 5 lapis

Blow per layer B 25 x 56 x

Volume mould V 1/30 ft³ 1/13,33 ft³

Compactive Effort CE 12375 ft . lbs/ ft³ 56250 ft . lbs/ ft

wSwGs

Gsw

d γγγ/11 +

=+

=Dry density :

Compactive effort :V

BLHWCE ×××=

Zero air void (saturated) S=100%: GswwGsVAZ.1

...+

=γ

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Compaction Curve

Water content

Dry

den

sity

(ρd)

optimum water content

ρd, max

Soil grains densely packed

- good strength and stiffness

- low permeability

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Compaction Curve

What happens to the relative quantities of the three phases with addition of water?

soil

water

air

Water content

Dry

den

sity

(ρd)

difficult to expel all air

lowest void ratio and highest dry density at optimum w

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Zero Air Void Curve

All compaction points should lie to the left of ZAV curve

corresponds to 100% saturation

Water content

Dry

den

sity

(ρd)

Zero air void curve (S=100%)

s

wsd wG

G+

=1

:Eq ρρS<100%

S>100% (impossible)

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Effect of Compactive Effort

Increasing compactiveeffort results in:

Lower optimum water content

Higher maximum dry density

E1

E2 (>E1)

Water content

Dry

den

sity

(ρd)

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Line of Optimum

Water content

Dry

den

sity

(ρd)

Compaction curves for different efforts

Line of optimum

Field Compaction

Pneumatic rubber tired roller

Different types of rollers (clockwise from right):

Vibratory roller

Smooth-wheel roller

Sheepsfoot roller

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Field Compaction

Compacts effectively only to 200-300 mm; therefore, place the soil in shallow layers (lifts)

Smooth Wheeled Roller

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Field Compaction

for compacting very small areas

Vibrating Plates

effective for granular soils

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Field Compaction

Provides kneading action; “walks out” after compaction

Sheepsfoot Roller

Very effective on clays

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Field Compaction

Provides deeper (2-3m) compaction. e.g., air field

Impact Roller

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Compaction Control

-a systematic exercise where you check at regular intervals whether the compaction was done to specifications.

e.g., 1 test per 1000 m3 of compacted

soil• Minimum dry density• Range of water content

Field measurements (of ρd) obtained using

• sand cone

• nuclear density meter

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Compaction Control Test

compacted ground

ρd,field = ?wfield = ?

Compaction specifications

Compare!

w

ρd

Dynamic Compaction

- pounding the ground by a heavy weightSuitable for granular soils, land fills and karst terrain with sink holes.

Crater created by the impact

Pounder (Tamper) solution cavities in limestone

(to be backfilled)

Dynamic Compaction

Pounder (Tamper)Mass = 5-30 tonneDrop = 10-30 m

Dynamic Compaction

Vibroflotation

Vibroflot (vibrating unit)Length = 2 – 3 mDiameter = 0.3 – 0.5 mMass = 2 tonnes

Practiced in several forms:

vibro–compaction

stone columns

vibro-replacement

Suitable for granular soils

(lowered into the ground and vibrated)

Vibroflotation

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Stone Columns

vibrator makes a hole in the weak ground hole backfilled ..and compacted Densely compacted stone

column

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Blasting

Aftermath of blastingFireworks?

For densifying granular soils

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Earthmoving Equipment

Large Excavator (see minivan on left for scale)

David and Goliath?

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Grader for spreading soil

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Bulldozer for spreading soil evenly

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Loader

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Backhoe

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Crawler mounted Hydraulic Excavator

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Rock Breaker

California Bearing Ratio (CBR)

CBR tests are performed primarily on soils in proposed road ways and other construction such as parking lots as one factor in determining the proper pavement thicknessCBR test require a laboratory compaction test, a four day soak in water (complete saturation) and load application by a CBR press

California Bearing Ratio (CBR)

Percobaan CBR dilakukan dengan melakukan penetrasi dari piston silinder (diameter 5 cm ) kedalam massa tanah dengan kecepatan 0,05 in / menit.CBR ditetapkan sebagai perbandingan dari percobaan pembebanan danstandard beban,diekspressikan dalam nilai prosentase.

CBR = TEST UNIT LOAD (psi) X 100%STANDARD UNIT LOAD (psi)

CBR

Hubungan CBR dengan jenis tanah :Di bawah ini diberikan tabel nilai CBR dari kondisi yang amat buruk dalam hubungannya dengan jenis tanah yang diklasifikasikan menurut UNCS

CBR KONDISI PENGGUNAAN KLASIFIKASI TANAH

0 - 3 Amat buruk Sub - grade OH, CH, MH, OL3 - 7 Buruk Sub - grade OH, CH, MH, OL7 - 20 Cukup Sub - base OL, CL, MC, SC,SM,SP20 - 50 Baik Base, Sub - base GM, GC, SW, SM, SP,BP

50 Amat Baik Base GW, GM

04 Kuliah 2 2

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