enci 5791 compaction in-situ soils used as: –bases for the construction of highway pavements...

ENCI 579 1

Compaction

• In-situ soils used as:– Bases for the construction of highway

pavements– embankments or leveling material for

construction projects

• Compacted to improve their density: M/V– improves the soil’s strength– lowers it’s permeability– reduces future settlement

ENCI 579 2

Compaction

• Evaluation of density as a result of compactive efforts with rollers and other equipment– common quality control measurement on soils

at construction sites– density of a compacted soil is measured and

compared to a density goal previously determined in laboratory tests

ENCI 579 3

Compaction Maximum Dry Density

• Maximum dry density must be established for each soil type– clay soil after compactive effort 2000 Kg/m3– granular soil with no compactive effort may be

well above this

• Dry density of a soil fn (water content)

ENCI 579 4


ENCI 579 5


Compaction Control

Determine the maximum dry density for a particular soil under a certain compactive effort and the water content at which this density is reached.

MD/V

ENCI 579 6


ENCI 579 7


• Compaction Test– Moisture density test– Proctor test

• soil is compacted into 10 cm diameter mold for material passes 4.75 mm sieve (15 cm mold for coarser material)

• soil is placed in 3 layers • each layer compacted 25 blows with a 2.5 Kg

hammer dropping 30 cm ( 56 blows)

ENCI 579 8


• 25 blow/56 blow compactive efforts are the same and represent the compactive efforts of 1930 construction rollers

• Compaction Test– sample of soil is mixed with water

• mass of compacted sample is measured

• water content determined

– sample of soil is mixed with more water– repeated until density decreases

ENCI 579 9


• Modified Compaction Test– Modified Moisture Density Test– Modified Proctor Test

• Increased loading on our pavements• Increased compactive effort of equipment• Revised test of higher compactive effort is now

often used– 4.5 Kg hammer, 45 cm drop, 5 layers– higher maximum dry density/lower w/c

ENCI 579 10


Density SampleMass of soil plus mold = 5321 gMass of mold = 3449 g

Water content sampleMass of sample plus container = 252.60gMass of dry sample plus container = 238.04 gMass of container = 104.73 g

Calculations: Water content sampleMass of water = 14.56 gMass of dry soil = 133.31 gWater content (w) = 14.56 g/133.31 g = 10.9%

From density sampleMass of soil in mold = 1872 g (4.127lb)Density (1872 g/943,9cm3)* = 1.983 g/cm3

Dry density (1983 kg/m3/1.109)** = 1788 kg/m3Mass

*Volume of standard mold is 943.9 cm3

**Dry density = density/(1+w)

ENCI 579 11


Zero Air Voids (ZAV) Curve

• “the maximum theoretical density of a soil at various water contents” with no air left in the soil water mixture

ZAV D = W

1/RD + W

ENCI 579 12

ENCI 579 13


• Maximum Dry Density of a soil is used in quality control

• Specification requires a certain % of maximum dry density at optimum water content found by the compaction test for that particular soil– Ensures density– Reduces the compactive effort

ENCI 579 14


Table 3-1MAXIMU DRY DENSITY AND OPTIMUM MOISTURE

CONTENT (TYPICAL)AASHTO

ClassificationMaximum DryDensity (kg/m3)

Optimum MoistureContent (%)

A – 1 Granular 1850-220 7-15A – 2 Sands 1750-2150 9-18A – 3 1750-1850 10-18A – 4 Silts 1500-2100 10-20A – 5 1400-1650 15-30A – 6 Clays 1500-1900 10-25A – 7 1400-1850 15-30

1400-

ENCI 579 15


ENCI 579 16


Note:

• If the soil was below optimum water content it may be necessary to add water by spraying

• The most important factor required for successful compaction is having the correct water content

ENCI 579 17

Compaction Field Density Tests

• Sampling Methods– sample of compacted material taken– dry mass of the soil taken is determined– volume originally occupied by the sample is

measured– field dry density = dry mass/volume of sample

• Two sampling methods– balloon densometer– sand cone apparatus

ENCI 579 18


• Balloon densometer– Dry mass of the soil is determined– Volume of the sample hole is found by forcing

a liquid filled balloon into the test hole– A rubber membrane allows the fluid to fill all

the cavities of the hole– The volume of fluid required is measured– density calculated– water content determined

ENCI 579 19


• Sand Cone Apparatus– Dry mass of the soil is determined– Volume of the test hole is obtained from the

mass of loose sand required to fill the hole– Sand is a uniform medium sand with a constant

loose density– Volume=mass of sand / loose density of sand– density is calculated– water content determined

ENCI 579 20


Example 3-4 Sand-Cone Apparatus: A sand cone holds 851.0 g. The loose density of the sand is 1.430 g/cm3

Field Test Results:

Total weight of the soil 639.5 g

Dry weight of the soil 547.9 g

Initial weight of the sand-cone apparatus 4527.8g

final weight of the sand-cone apparatus 3223.9g

ENCI 579 21


Calculations:Mass of the sand used 4527.8g-3223.9g = 1303.9g

Mass in test hole 1303.9g-851.0g = 452.9 g

Volume of test hole 452.9 g = 316.7 cm3

1.430 g/cm3

Field dry density 547.9g/316.7 cm3 = 1.730 g/ cm3

Field water content 639.5-547.9 = 16.7%

547.9

ENCI 579 22


• Nuclear Moisture-Density Gauge– Results are available within minutes

• Increases equipment efficiency

• Know that your construction methods are correct

– Gamma rays are emitted into the soil• absorbed by the soil according to it’s density

• rays that pass through the soil are measured by a detector

• density is then calculated

ENCI 579 23


• Nuclear Moisture-Density Gauge– Neutron radiation emitted into the soil

• neutrons loose energy when they collide with hydrogen atoms in the soil water

• detector measures the amount of moderated neutrons

• water content can be calculated

– Direct transmission mode– Backscatter mode

ENCI 579 24


ENCI 579 25


• Corrected Maximum Dry Density– compaction test is usually done on materials

finer than 4.75 mm– sample contains coarse grained sized particles

• gravel in a soil composed mainly of fine grains can be compacted to 90% of their theoretical maximum density

• assuming gravel RD=2.65

ENCI 579 26


Example Laboratory maximum density of a soil is 1900 kg/m3. Specifications require 95% compaction. In the filed, dry density of the soil is found to be 1810kg/m3. A visual check of the soil in the field indicates that it contains about 20% gravel sizes. (Scales can be used for a more accurate determination of the percentage of gravel.) Check for compaction.

ENCI 579 27


Corrected maximum dry density is:

0.80 x 1900kg/m3 + 0.20 x (90% x 2.65 x 1000kg/m3 = 1520 kg/m3 + 477kg/m3 = 1997kg/m3

Percent compaction is 1810/1997 = 90.6% and is not acceptable

ENCI 579 28

Compaction Operation and Quality Control

• Highway components that require compaction:– Subgrade (15-30cm) in depth, provides the

foundation for the pavement structure– Fill material used to bring the soil surface up to

the subgrade level (15-30 cm compacted lifts)– Backfill material– Layers in granular material used in pavement– Asphalt layers at the surface

ENCI 579 29

Compaction Compaction Equipment

• Compaction Equipment– Consists of various types of rollers and tamping

equipment– self propelled– compacting wheels equipped to vibrate

• 1500-2500 cycles/minute for most soils and granular materials

– smooth steel drums– drums with pads or “feet”– rubber tires

ENCI 579 30


• Vibratory Smooth Drum Rollers– one steel drum and rubber tired drive wheels– two steel drums one of which is the driver– effective for gravel, sand, silt soils– granular base courses and asphalt mixtures– mass of the drum is between 2-15 tonnes– utilized in layers from 0.5-1.0 meters in depth– usually require 3-5 passes to produce specified

density

ENCI 579 31


• Vibratory Smooth Drum Rollers

ENCI 579 32


• Padded Wheel or “Sheep’s Foot” Rollers– pads on the rotating drum and may vibrate– effective in clay and silty clay soils– punching action breaks the clay’s bonds which

resist rearrangement of the grain structure– pressure exerted by the pad 1000-5000 kpa

depending on the size of the roller– utilized in layers of 15-30 cm in depth– usually require 3-5 passes to achieve density

ENCI 579 33


• Padded Wheel or “Sheep’s Foot” Rollers

ENCI 579 34


• Pneumatic Tire Rollers– 2-12 rubber tires on each axle– individual tires wobble or weave or move lower

than adjacent tires to improve the kneading action

– effective in clay and granular soils and asphalt mixtures can be kneaded and compacted

– effective depths for soils or base courses is up to 15 cm (larger units of 40-50 tonnes 30 cm)

ENCI 579 35


• Pneumatic Tire Rollers

ENCI 579 36


• Smooth Drum Non-vibratory Rollers– used for finishing or sealing passes on soils and

granular layers– final leveling passes on asphalt layers

• Vibrating Plates or Tampers– used for trench backfills– around structures where larger equipment can’t

operate– larger tamping equipment is usually attached to

excavators or other equipment

ENCI 579 37

Compaction Quality Control

• Determine which materials are to be sampled and tested

• Frequency of the testing and type of tests to be performed on the material

• Transportation authorities usually have specifications outlining these criteria– Moisture Density 1/ soil type (or 5000 m subgrade)

– Field Compaction 4/500 m of each layer

• Method Specification vs EPS Specifications

enci 5791 compaction in-situ soils used as: –bases for the construction of highway pavements...

Documents

maximum theoretical

density decreases

density goal

construction sites density

successful compaction

compactive effort slide

soil fn water content

compacted soil