ConsistenceConsistenceof the Soilof the Soil

GES 394 GES 394 Revised by Mr. Brian OramRevised by Mr. Brian Oramhttp://www.water-research.nethttp://www.water-research.net

WHAT IS Consistency ?WHAT IS Consistency ? Soil consistence provides a means of describing the degree and kind of Soil consistence provides a means of describing the degree and kind of

cohesion and adhesion between the soil particles as related to the resistance cohesion and adhesion between the soil particles as related to the resistance of the soil to deform or rupture. of the soil to deform or rupture.

Since the consistence varies with moisture content, the consistence can be Since the consistence varies with moisture content, the consistence can be described as dry consistence, moist consistence, and wet consistence. described as dry consistence, moist consistence, and wet consistence.

Consistence that is evaluated includes rupture resistance and stickiness. Consistence that is evaluated includes rupture resistance and stickiness.

The rupture resistance is a field measure of the ability of the soil to The rupture resistance is a field measure of the ability of the soil to withstand an applied stress or pressure as applied using the thumb and withstand an applied stress or pressure as applied using the thumb and forefinger.forefinger.

Quick ReviewQuick Review

Cohesion Cohesion is the attraction of one water is the attraction of one water molecule to another resulting from hydrogen molecule to another resulting from hydrogen bonding. bonding.

Adhesion Adhesion is similar to cohesion except with is similar to cohesion except with adhesion involves the attraction of a water adhesion involves the attraction of a water molecule to a non-water molecule.molecule to a non-water molecule.

When We Describe Consistency – When We Describe Consistency – We Attempt to Describe the FollowingWe Attempt to Describe the Following

Environmental Applications (our focus)Environmental Applications (our focus)– Rupture Resistance – Moist and Dry Rupture Resistance – Moist and Dry

ConsistencyConsistency– Stickiness – Wet ConsistencyStickiness – Wet Consistency– Plasticity- Wet ConsistencyPlasticity- Wet Consistency

Geophysical / EngineeringGeophysical / Engineering– Manner and Type of Failure Manner and Type of Failure – Penetration ResistancePenetration Resistance

Rupture ResistanceRupture Resistance

A measure of the strength of the soil to A measure of the strength of the soil to withstand an applied stresswithstand an applied stress

Moisture content is also consideredMoisture content is also considered– DryDry– Moist (field capacity)Moist (field capacity)

Dry ConsistencyDry Consistency

Class Description

Loose Noncoherent Symbol L or LO or lo

Soft (<8 N) Soil crushes under very low pressure

Slightly Hard (8 to < 20 N) Soil material crushes- low pressure - little resistance

Mod Hard (20 to < 40 N) Soil material crushes- moderate pressure -resistance

Hard (40 to < 80 N) Soil material crushes under strong pressure

Very Hard (80 to < 160 N) Can not be crushed between thumb and forefinger.

Extremely Hard Pressure applied by foot with full body

1 Newton (N) = 0.224 lb/ft

Dry and Moist ConsistencyDry and Moist Consistency

MoistMoist DryDry

StressStressSpecimen Specimen FailsFails

LooseLoose LooseLoose 00

Very FriableVery Friable SoftSoft < 8 N< 8 N

FriableFriable Slightly HardSlightly Hard 8 to < 20 N8 to < 20 N

FirmFirm Moderately HardModerately Hard 20 to < 40 N20 to < 40 N

Very FirmVery Firm HardHard 40 to < 80 N40 to < 80 N

Extremely FirmExtremely Firm Very HardVery Hard 80 to < 160 N80 to < 160 N

1 Newton (N) = 0.224 lb/ft

Wet ConsistencyWet Consistency

Describe Stickiness- Describe Stickiness- – The capacity of soil to adhere to other The capacity of soil to adhere to other

objectsobjects– Estimated at moisture content that Estimated at moisture content that

displays maximum adherence between displays maximum adherence between thumb and fore fingerthumb and fore finger

Describe PlasticityDescribe Plasticity– Degree a soil can be molded or reworked Degree a soil can be molded or reworked

causing permanent deformation without causing permanent deformation without rupturing. rupturing.

Stickiness ClassesStickiness Classes Non-StickyNon-Sticky – little or no soil adheres to fingers after release of – little or no soil adheres to fingers after release of

pressurepressure

Slightly StickySlightly Sticky – soil adheres to both fingers after release of – soil adheres to both fingers after release of pressure with little stretching on separation of fingerspressure with little stretching on separation of fingers

Moderately Sticky – Moderately Sticky – soil adheres to both fingers after release soil adheres to both fingers after release of pressure with some stretching on separation of fingersof pressure with some stretching on separation of fingers

Very Sticky - Very Sticky - soil adheres firmly to both fingers after release soil adheres firmly to both fingers after release of pressure with stretches greatly on separation of fingersof pressure with stretches greatly on separation of fingers

Non-StickyNon-Sticky

Very StickyVery Sticky

Slightly-Slightly-StickySticky

PlasticityPlasticity

The degree to which puddled or The degree to which puddled or reworked soil can be permanently reworked soil can be permanently deformed without rupturingdeformed without rupturing

Evaluation done by forming a 4 cm Evaluation done by forming a 4 cm long wire of soil at a water content long wire of soil at a water content where maximum plasticity is where maximum plasticity is expressedexpressed

Plasticity ClassPlasticity Class Non-PlasticNon-Plastic – will not form a 6 mm dia, 4 cm long wire, or if – will not form a 6 mm dia, 4 cm long wire, or if

formed , can not support itself if held on endformed , can not support itself if held on end

Slightly PlasticSlightly Plastic – 6 mm dia, 4 cm long wire wire supports – 6 mm dia, 4 cm long wire wire supports itself, 4 mm dia, 4 cm long wire wire does notitself, 4 mm dia, 4 cm long wire wire does not

Moderately PlasticModerately Plastic – 4 mm dia, 4 cm long wire wire supports – 4 mm dia, 4 cm long wire wire supports itself, 2 mm dia, 4 cm long wire wire does notitself, 2 mm dia, 4 cm long wire wire does not

Very PlasticVery Plastic – 2 mm dia, 4 cm long wire wire supports itself – 2 mm dia, 4 cm long wire wire supports itself

Estimating Clay MineralogyEstimating Clay MineralogyUsing Consistence and ColorUsing Consistence and Color

2:1 Clay- Montmorillonite2:1 Clay- Montmorillonite

High Shrink and Swell Potential

1:1 Clay- Kaolinite1:1 Clay- Kaolinite

ConsistenceConsistenceof the Soilof the Soil

GES 394 GES 394 Revised by Mr. Brian OramRevised by Mr. Brian Oramhttp://www.water-research.nethttp://www.water-research.net