Earthwork:Earthwork:Use of Fine Grained & Use of Fine Grained & Granular MaterialGranular Material

IntroductionIntroduction

Earthwork consists of:Earthwork consists of:– Material excavations (cuts)Material excavations (cuts)– Material embankments (fills)Material embankments (fills)

Common types of work:Common types of work:– Roadways & Transportation SystemsRoadways & Transportation Systems– Foundations SystemsFoundations Systems– Water Management Systems Water Management Systems

(ponds, channels, etc.)(ponds, channels, etc.)

Importance of Soil Importance of Soil QualityQuality

If pavement is to remain smooth & If pavement is to remain smooth & stable..stable..

AND AND

If structures are to remain stable and If structures are to remain stable and undamaged due to settlement…..undamaged due to settlement…..

THE SOIL ON WHICH THEY ARE BUILT MUST THE SOIL ON WHICH THEY ARE BUILT MUST ALSO BE STABLE AND MUST FURNISH ALSO BE STABLE AND MUST FURNISH UNIFORM SUPPORT! SUPPORT!

Materials Normally Materials Normally Suitable for Earthwork:Suitable for Earthwork:

Natural Soil Material: Natural Soil Material:

– Created by nature (except organics)Created by nature (except organics)– Material that is mined or excavatedMaterial that is mined or excavated

Material must have a laboratory dry weight Material must have a laboratory dry weight of at least 90 lbs. per cubic footof at least 90 lbs. per cubic foot

Materials that weight less generally have too Materials that weight less generally have too much organic matter …this leads to much organic matter …this leads to excessive compressibilityexcessive compressibility

Materials Normally Materials Normally Suitable for EarthworkSuitable for Earthwork Natural Granular Materials:Natural Granular Materials:

– Includes broken rock, gravel, sand, Includes broken rock, gravel, sand, durable siltstone, durable sandstone durable siltstone, durable sandstone that can be placed in 8” loose lifts.that can be placed in 8” loose lifts.

– These are generally mixtures of These are generally mixtures of coarse & fine particle sizescoarse & fine particle sizes

Engineering Properties of Engineering Properties of Granular Soils Granular Soils (Sand & Gravel)(Sand & Gravel)

1.1. Good foundation & embankment Good foundation & embankment materialmaterial

2.2. Not frost susceptible & are free Not frost susceptible & are free drainingdraining

3.3. May erode on embankment side slopesMay erode on embankment side slopes

4.4. Identified by particle sizeIdentified by particle size

5.5. Easily compacted when “well graded”Easily compacted when “well graded”

Engineering Properties of Engineering Properties of Fine Grained Soils (Clay & Fine Grained Soils (Clay & Silt)Silt)

1.1. Often have low strengths Often have low strengths (crush under load)(crush under load)

2.2. Plastic & compressiblePlastic & compressible3.3. Lose strength when wet or disturbedLose strength when wet or disturbed4.4. Practically imperviousPractically impervious5.5. Slopes are prone to sliding & erodingSlopes are prone to sliding & eroding6.6. Frost susceptibleFrost susceptible7.7. Shrink & swell with change in water Shrink & swell with change in water

contentcontent

Why is particle size Why is particle size important?important?

Soil’s performance is largely Soil’s performance is largely dependant on its particle size dependant on its particle size distribution (gradation)distribution (gradation)

For example:For example:

– Backfill behind a retaining wall must be Backfill behind a retaining wall must be free drainingfree draining

WHAT MATERIAL TYPE WOULD WE WHAT MATERIAL TYPE WOULD WE WANT?WANT?

Why is particle size Why is particle size important?important?

For example: For example:

We want a free draining compactable soil for a sub base beneath a We want a free draining compactable soil for a sub base beneath a foundation.foundation.

Stated previously:Stated previously:

– compactability of soil largely depends on “gradation” or “grain compactability of soil largely depends on “gradation” or “grain size distribution”size distribution”

WHAT HAPPENS TO YOU WHEN YOU STEP ON A PILE WHAT HAPPENS TO YOU WHEN YOU STEP ON A PILE OF GRAVEL OF UNIFORM SIZE?OF GRAVEL OF UNIFORM SIZE?

WHAT IF THE GRAVEL WAS MIXED WITH SAND WHAT IF THE GRAVEL WAS MIXED WITH SAND AND SMALLER PARTICLES?AND SMALLER PARTICLES?

Load carrying Load carrying capacity will be capacity will be

affected by particle affected by particle size distributionsize distribution

Construction SpecificationsConstruction Specifications

Construction project specifications set limits Construction project specifications set limits for particle size based on the required for particle size based on the required performance of the soil/materialperformance of the soil/material

Engineer will require certain soil/material Engineer will require certain soil/material characteristicscharacteristics

Soil/material must be tested in the lab to Soil/material must be tested in the lab to determine suitability for the projectdetermine suitability for the project

FOR EXAMPLE:FOR EXAMPLE:

Soil ClassificationSoil Classification

Soils are classified according the Soils are classified according the grain size distributiongrain size distribution

Both ASTM & AASHTO Both ASTM & AASHTO classification systems reference classification systems reference sieve analysissieve analysis

We Can Also Accurately Describe Soil TextureWe Can Also Accurately Describe Soil Texture

Soil texture refers to the relative proportion of sand, silt and clay size particles in a sample of soil.

Soils that are dominated by clay are called fine textured soils.

Those dominated by larger particles are referred to as coarse textured soils

Soil Texture Triangle:Soil Texture Triangle:– Sieve analysis will reveal % sand, silt, clay (see graph)Sieve analysis will reveal % sand, silt, clay (see graph)– What is the texture class for a soil having 45% clay, 45% silt, and 10% What is the texture class for a soil having 45% clay, 45% silt, and 10%

sand?sand?

Gradation ExamplesGradation Examples

Sieve Size InformationSieve Size Information

Lab ProceduresLab Procedures Particle Size Analysis testing is Particle Size Analysis testing is

broken down into 2 parts:broken down into 2 parts:– 1. Sieve analysis (Sand & Gravel Portion)1. Sieve analysis (Sand & Gravel Portion)– 2. Hydrometer analysis (Silt & Clay 2. Hydrometer analysis (Silt & Clay

Portion)Portion)

Today’s Lab:Today’s Lab:Particle Size Analysis of Particle Size Analysis of Coarse Grained Coarse Grained MaterialMaterial

ASTM D-422ASTM D-422

We will determine “gradation”, or We will determine “gradation”, or also referred to “particle size also referred to “particle size distribution” of a granular soildistribution” of a granular soil

Our Lab AgendaOur Lab Agenda

Sieve Analysis This LabSieve Analysis This Lab Hydrometer Analysis Next LabHydrometer Analysis Next Lab