compaction geotechnical engineering

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Instructor: Dr. RICARDO ZAURIN

University of Central FloridaCivil, Environmental, and Construction Engineering

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CompactionCompaction

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What is compaction?What is compaction?

A simple ground improvementtechnique, where the soil is densifiedthrough external compactive effort.

A simple ground improvementtechnique, where the soil is densifiedthrough external compactive effort.

Soil CompactionSoil Compaction

Increase Unit WeightIncrease StrengthIncrease Bearing Capacity of

FoundationsReduces water seepage, swelling

and contraction.Reduce settlementsIncrease stability of embankments

Increase Unit WeightIncrease StrengthIncrease Bearing Capacity of

FoundationsReduces water seepage, swelling

and contraction.Reduce settlementsIncrease stability of embankments

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Soil Compaction HOW?Soil Compaction HOW?

By removing trapped AirBy removing trapped Air

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+ water =

Compactive effort

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Compaction CurveWhen enough is enough?

Compaction CurveWhen enough is enough?

Water content

Dry

den

sity

( d

)

optimum water content (OMC)

d, max

Soil grains densely packed

- good strength and stiffness

- low permeability

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Zero Air Void CurveZero Air Void Curve

All compaction points should lie to the left of ZAV curve

- corresponds to 100% saturation

Water content

Dry

den

sity

( d

)

Zero air void curve (S=100%)

S<100%S>100% (impossible)

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Effect of Compactive EffortEffect of Compactive EffortIncreasing compactive effort results in:

E1

E2 (>E1)

Water content

Dry

den

sity

( d

)

E3

(>E2)

Lower optimum water content

Higher maximum dry density

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Line of OptimumLine of Optimum

Water content

Dry

den

sity

( d

)

Compaction curves for different efforts

Line of optimum

Field CompactionField Compaction

Pneumatic rubber tired rollerPneumatic rubber tired roller

Different types of rollers

Vibratory roller Smooth-wheel roller

Sheepsfoot roller

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

Smooth Wheeled Roller

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for compacting very small areas

Vibrating Plates

effective for granular soils

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Provides kneading action- 6 in layers

Sheepsfoot Roller

Very effective on clays

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Provides deeper (2-3m) compaction.

Impact Roller

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Principles of Geotechnical Engineering Braja M. Das

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Principles of Geotechnical Engineering Braja M. Das

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Compaction ControlCompaction 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 d) obtained using

• sand cone

• nuclear density meter

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Laboratory Compaction TestLaboratory Compaction Test- to obtain the compaction curve and define the optimum water content and maximum dry density for aspecific compactive effort.

hammerStandard Proctor: Modified Proctor:

• 3 layers

• 25 blows per layer

• 5 layers

• 25 blows per layer

• 2.5 kg hammer

• 300 mm drop

• 4.54 kg hammer

• 450 mm drop

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CE=Compaction Energy per unit volume(Compaction Effort)

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There are correlations between OMC(w), CE, PL, and d for cohesive soils

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Compaction Control TestCompaction Control Test

compacted ground

d,field = ?wfield = ?

Compaction specifications

Compare!

w

d

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Compaction Control TestCompaction Control Test

1.- Sand Cone Method

2.- Rubber Balloon Method

3.- Nuclear Method

1.- Sand Cone Method

2.- Rubber Balloon Method

3.- Nuclear Method

Sand Cone MethodSand Cone Method

ASTM D-1556 Glass (or plastic) jar with a

metal cone Ottawa sand (known wt. &

vol.) Dig a hole – weigh the soil

and obtain w(%) Fill the hole with sand Determine the new wt. & vol. Eventually, d = (dry wt. of excavated

soil)/vol. of hole

ASTM D-1556 Glass (or plastic) jar with a

metal cone Ottawa sand (known wt. &

vol.) Dig a hole – weigh the soil

and obtain w(%) Fill the hole with sand Determine the new wt. & vol. Eventually, d = (dry wt. of excavated

soil)/vol. of hole

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Determine The combined Weight of Jar, Cone, and Sand (W1)

Determine the Weight of the Dry Soil W3=W2/(1+w)

In the Field, Excavate a Small Hole (Keep the Soil)

Moist Content (w)

Weight of Soil (W2)


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Close the Valve and Place the Jar Inverted. Open the Valve and Allow Sand to fill the Hole. Close the Valve

Determine the weight of the remaining sand +Jar+Cone (W4)

Weight of sand to fill the Hole + Cone (W5)

W5=W1-W4

After Hole has been excavated


W5: Weight of sand to fill hole + cone

Wc: Weight of sand to fill the cone (From Lab Calibration

Dry unit weight of Ottawa sand used


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Rubber Balloon MethodRubber Balloon Method

ASTM D-2167

Similar to sand cone

Vol. is measured utilizing a

rubber balloon filled with

water

ASTM D-2167

Similar to sand cone

Vol. is measured utilizing a

rubber balloon filled with

water

Nuclear MethodNuclear Method

Emits gamma rays

Detects how the gamma

rays travel thru soil

Amounts of gamma rays

detected correlate with the

unit weight of soil

Emits gamma rays

Detects how the gamma

rays travel thru soil

Amounts of gamma rays

detected correlate with the

unit weight of soil

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Specification for Field Compaction

Specification for Field Compaction

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In most specifications for earthwork, the contractor is instructed to achieve a compacted field unit weight of 90% to 95% (up to 98%) of the maximum dry unit weight determined in the Laboratory

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Special Compaction TechniquesSpecial Compaction Techniques

Dynamic

Vibroflotation

Blasting

Dynamic

Vibroflotation

Blasting

Dynamic CompactionDynamic Compaction- pounding the ground by a heavy weight

Suitable 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)

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Dynamic CompactionDynamic Compaction

Pounder (Tamper)Weight (Wh)= 80-360kN (18-80kip)Drop(h) = 7.5-30.5 m (25-100ft)

D=Depth of densification

Dynamic CompactionDynamic Compaction

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Important Dynamic Compaction Construction Conditions:

Minimum 100-150 ft clearance from any structure. Review site for vibration sensitivity.

Dynamic Compaction Acceptance Testing:

Large-Scale Load Test . Standard Penetration Test (SPT). Cone Penetrometer Test (CPT). Pressuremeter Test (PMT). Dilatometer Test (DMT). Shear-Wave Velocity Profile.

Important Dynamic Compaction Construction Conditions:

Minimum 100-150 ft clearance from any structure. Review site for vibration sensitivity.

Dynamic Compaction Acceptance Testing:

Large-Scale Load Test . Standard Penetration Test (SPT). Cone Penetrometer Test (CPT). Pressuremeter Test (PMT). Dilatometer Test (DMT). Shear-Wave Velocity Profile.

Vibro-CompactionKnown as “VibroFlotation“.Is used to densify clean,

cohesionless soils.The action of the vibrator, usually

accompanied by water jetting. Allowing them to move into a

denser configuration, typically achieving a relative density of 70 to 85 percent.

Known as “VibroFlotation“.Is used to densify clean,

cohesionless soils.The action of the vibrator, usually

accompanied by water jetting. Allowing them to move into a

denser configuration, typically achieving a relative density of 70 to 85 percent.

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Expected Vibro-Compaction Results:Expected Vibro-Compaction Results:

Relative EffectivenessGround Type

ExcellentSands

Marginal to GoodSilty Sands

PoorSilts

Not applicableClays

VibroflotationVibroflotation

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

Practiced in several forms:

vibro–compaction

stone columns

vibro-replacement

Suitable for granular soils

(lowered into the ground and vibrated)

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Stone ColumnsStone Columns

vibrator makes a hole in the weak ground

hole backfilled ..and compacted Densely compacted stone column


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Typical Patterns for Vibroflot ProbesTypical Patterns for Vibroflot Probes

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Effective Range of Soil for VibroflotationEffective Range of Soil for Vibroflotation

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Zone 1 - Most Suitable

Zone 2 – Lower limit for effectiveness For finer soils considerable effort has to be used

Zone 3 - Too much gravel. Rate of Probe penetration my be slow and uneconomical.

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Grain Size Distribution of the Backfill Material for Vibroflotation

Grain Size Distribution of the Backfill Material for Vibroflotation

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Range of SN Rating as Backfill

0-10 Excellent

10-20 Good

20-30 Fair

30-50 Poor

>50 Unsuitable Brown(1977)

BlastingBlasting

Aftermath of blasting

For densifying granular soils

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Blasting

Blasting is the process of detonating small charges within loose cohesion less soils for the purpose of densification.

Blasting is the process of detonating small charges within loose cohesion less soils for the purpose of densification.

Expected Soil Behavior with Blasting:

Immediate and long-term surface settlement.

Settlement can be 2-10 percent of treated strata thickness.

Penetration resistance will increase slowly with time for several weeks.

Dense zones may be loosened during blasting.

Expected Soil Behavior with Blasting:

Immediate and long-term surface settlement.

Settlement can be 2-10 percent of treated strata thickness.

Penetration resistance will increase slowly with time for several weeks.

Dense zones may be loosened during blasting.

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Design Considerations:

Charges should be placed at approximately 1/2-3/4 of desired depth of compaction.

Spacing of detonation holes should be between 5-15 m.

Successive coverage's are separated by hours or days.

Individual charge 1-12 kg, the amount of total explosive is 89-150 g/m^3 of treated soil.

Soil closest to the surface will be poorly compacted and may need compaction by another method or removal.

The compaction resulting from blasting is a function of the initial relative density.

Design Considerations:

Charges should be placed at approximately 1/2-3/4 of desired depth of compaction.

Spacing of detonation holes should be between 5-15 m.

Successive coverage's are separated by hours or days.

Individual charge 1-12 kg, the amount of total explosive is 89-150 g/m^3 of treated soil.

Soil closest to the surface will be poorly compacted and may need compaction by another method or removal.

The compaction resulting from blasting is a function of the initial relative density.

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Earthmoving EquipmentEarthmoving Equipment

Grader for spreading soil

This self-loading scraper is equipped with mixers inside its bucket. It scrapes up mixes it within its bucket, and then spreads it back over the ground surface.

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Bulldozer

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Backhoe

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Rock Breaker

CompactionCompaction

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ExamplesExamples

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Proctor Test ExampleProctor Test ExampleFor the following Standard Proctor Test data

– Plot the compaction curve

– Obtain the Maximum Dry Density and the OMC

Plot the ZAV curve if Gs=2.75

For the following Standard Proctor Test data– Plot the compaction curve

– Obtain the Maximum Dry Density and the OMC

Plot the ZAV curve if Gs=2.75

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Proctor Test ExampleProctor Test Example

We need Moist Content and Dry densityWe need Moist Content and Dry density

(1) (2) (3) (4)(5)

(2)-(3)(6)

(3)-(1)(5)/(6)

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We need Moist Content and Dry densityWe need Moist Content and Dry density

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Proctor Test Example ZAVProctor Test Example ZAV

Assigned Values

105.00

107.00

109.00

111.00

113.00

115.00

117.00

119.00

121.00

123.00

0.00 5.00 10.00 15.00 20.00 25.00

Gam

ma

Dry

(lb/

ft3)

Moist Content (%)

Compaction Curve

Compaction Curve

ZAV Curve

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Revision for Test 1Revision for Test 1

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compaction geotechnical engineering

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