soil compaction tests

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A compaction test is a soil quality test used to assess the level of compaction which can occur in

the soil on a site. Compaction tests are commonly performed as part of a geotechnical profile of

a building site. They may also be performed to learn more about a soil in a particular area,

whether or not the area is slated for development. Ageotechnical engineer, geologist, or

soilscientistmay conduct a compaction test.

The goal of asoil compactiontest is to find the maximum practical density of the soil. Forthetest, a sample of soil is packed into a mold and subjected to pressure to force the soil to

compact. The test is repeated several times, with the moisture level of the soil being adjusted

to achieve a range of values. The test results can be used to determine how much the soil can

compact, what the optimum moisture level on the site is, and what the maximum dry density of

the soil is.

The more moisture in the soil, the more it can be compacted. Compaction tests provide

important information about the soil quality at a site which can be used to determine where

the best building sites are, how much weight the soil can withstand, and whether or not the site

is even appropriate for building. These tests are on

Soil Compaction Tests

Posted inSoil Engineering| Email This Post

There are many types of Soil compaction tests which are performed on soil. Some of

these are :-

1) The Sand Cone Method

One of the most common test to determine the field density of soil is the sand-cone

method. But it has a major limitation that this test is not suitable for saturated and softsoils

The formula used are

Volume of soil, ft3

(m3)=[weight of sand filling hole, lb (kg)] /[ Density of sand,

lb/ft3 (kg/m3)]

% Moisture = 100(weight of moist soil weight of dry soil)/weight of dry soil

Field density, lb/ft3 (kg /m3)=weight of soil, lb (kg)/volume of soil, ft3 (m3)

Dry density=field density/(1 + % moisture/100)

% Compaction=100 (dry density)/max dry density

Maximum density is found by plotting a densitymoisture curve.
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2) California Bearing Ratio

The California bearing ratio (CBR) is used as a determine the quality of strength of a

soil under a pavement. It also measures the thickness of the pavement, its base, and

other layers.

CBR = F/Fo

where

F = force per unit area required to penetrate a soil mass with a 3-in2(1935.6-mm

2)

circular piston (about 2 in (50.8 mm) in diameter) at the rate of 0.05 in/min (1.27

mm/min)

F0 = force per unit area required for corresponding penetration of a standard material.

3) Soil Permeability

Darcys law is applicable in determining the soil permeability. Darcy law states that

V = kiAwhere

V = rate of flow, cm3 /s,

A = cross-sectional area of soil conveying flow, cm2

k = Coefficient of permeability which depends on grain-size distribution, void ratio and

soil fabric. The value varies from 10 cm/s for gravel to less than 107 for clays.

A compaction test is a soil quality test used to assess the levelof compaction which can occur in the soil on a site. Compaction tests arecommonly performed as part of a geotechnical profile of a building site. They may

also be performed to learn more about a soil in a particular area, whether or notthe area is slated for development. Ageotechnical engineer, geologist, orsoilscientistmay conduct a compaction test.In some cases, the test may be performed in situ, in which case the testingoptions may be more limited, and the profile will not be ascomplete. Compaction tests can also be performed in a lab environment with soilsamples taken from a site. The lab allows for more controls and more finesse ofthe test. Soil often needs to be taken back to the lab anyway for the performanceof additional soil quality tests which are designed to provide more informationabout the characteristics and composition of the soil.he goal of asoil compactiontest is to find the maximum practical density of the soil. For

the test, a sample of soil is packed into a mold and subjected to pressure to force thesoil to compact. The test is repeated several times, with the moisture level of the soilbeing adjusted to achieve a range of values. The test results can be used to determinehow much the soil can compact, what the optimum moisture level on the site is, andwhat the maximum dry density of the soil is.The more moisture in the soil, the more it can be compacted. Compaction tests provideimportant information about the soil quality at a site which can be used to determinewhere the best building sites are, how much weight the soil can withstand, and whether
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or not the site is even appropriate for building. These tests are one among manyassessments performed when evaluating sites to create a complete picture.The development of the soil compaction test is credited to Ralph R.Proctor, and it issometimes known as theProctor Test. Proctor developed the test in the 1930s, and themechanism of the test has not changed much since; for testing, a mold of standardized

size is used, with a mallet of standardized weight dropped from a standard height toachieve the desired level of pressure. Like other scientific tests, the compaction test isdesigned to be repeatable by anyone with a knowledge of the procedure and thestandard equipment.

Proctor compaction test

From Wikipedia, the free encyclopedia

The Proctor compaction test is a laboratory method of experimentally determining the

optimalmoisture contentat which a givensoiltype will become most dense and achieve

its maximum drydensity. The term Proctor is in honor ofR. R. Proctor, who in 1933

showed that the dry density of a soil for a given compactive effort depends on theamount of water the soil contains duringsoil compaction.[1]His original test is most

commonly referred to as the standard Proctor compaction test; later on, his test was

updated to create the modified Proctor compaction test.

These laboratory tests generally consist of compacting soil at known moisture content

into a cylindrical mould of standard dimensions using a compactive effort of controlled

magnitude. The soil is usually compacted into the mould to a certain amount of equal

layers, each receiving a number blows from a standard weighted hammer at a specified

height. This process is then repeated for various moisture contents and the dry

densities are determined for each. The graphical relationship of the dry density to

moisture content is then plotted to establish the compaction curve. The maximum dry

density is finally obtained from the peak point of the compaction curve and its

corresponding moisture content, also known as the optimal moisture content.

The testing described is generally consistent with theAmerican Society for Testing and

Materials(ASTM) standards, and are similar to theAmerican Association of State

Highway and Transportation Officials(AASHTO) standards. Currently, the procedures

and equipment details for the standard Proctor compaction test is designated by ASTM

D698 and AASHTO T99. Also, the modified Proctor compaction test is designated by

ASTM D1557 and AASHTO T180.

Theory of Soil compaction

Compaction is the process by which the bulk density of an aggregate of matter is

increased by driving out air. For any soil, for a given amount of compactive effort, the
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density obtained depends on the moisture content. At very high moisture contents, the

maximum dry density is achieved when the soil is compacted to nearly saturation,

where (almost) all the air is driven out. At low moisture contents, the soil particles

interfere with each other; addition of some moisture will allow greater bulk densities,

with a peak density where this effect begins to be counteracted by the saturation of the

soil.

Objective ofStandard Compaction test- To determine relation between water content and dry density ofsoil- To determine optimum water content and corresponding maximum dry density for soil- To determine relation between penetration resistance and water content forcompacted soil.

Importance of Standard Compaction test-Compaction increases the shear strength of the soil.

-Compaction reduces the voids ratio making it more difficult for water to flow throughsoil. This is important if the soil is being used to retain water such as would be requiredfor an earth dam.-Compaction can prevent the build up of large water pressures that cause soil to liquefyduring earthquakes.

CONCLUSION:The primary values determined in a compaction test are, of course theoptimum moisture content andmaximum dry unit weight, however, the written reportwould normally also include the compactioncurve data form. In addition, the origin of the

material tested, as well as a description of it, wouldnormally be included, together withan indication of the method used (A, B, or C) and the preparation(moist or dry).Type ofsoil is the primary factor affecting maximum dry unit weight and optimum moisturecontent fora given compactive effort and compaction method. Maximum dry unit weightsmay range from around60lb/ft3for organic soils to about 145 lb/ft3for well graduated, granular material containing just enoughfines to fill small voids.Optimum moisture contents may range from around 5% for granular material toabout35% for elastic silts and clays. Higher optimum moisture contents are generally

associated withlower dry unit weights. Higher dry unit weights are associated with well-graded granular materials.Uniformly graded sand, clays of high plasticity, and organicsilts and clays typically respond poorly tocompaction.DISCUSSION:To carry out alaboratory compaction test, a soil at a selected water content is placed in three layersintoa mold of given dimensions, with each layer compacted by 25 or 56 blows of a 5.5-lb(24.4-N) rammerdropped from a distance of 12 in. (305mm), subjecting the soil to a totalcompactive effort of about12,400ft-lb/ft3(600kN-m/m


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3). The resulting dry unit weight is determined. The procedure is repeated fora sufficientnumber of water contents to establish a relationship between the dry unit weight andthewater contents to establish a relationship between the dry unit weight and the watercontent for thesoil. These data, when plotted, represent a curvilinear relationship knownas the compaction curve. Thevalues of optimum water content and standard maximum

dry unit weight are determined from thecompaction curve.

Permeability influid mechanicsand theearth sciences (commonlysymbolized as , ork) is a measure of the ability of aporousmaterial(often, arockor unconsolidated material) to allow fluids topass through it.

Applications

The concept of permeability is of importance in determining the flow

characteristics ofhydrocarbonsinoilandgasreservoirs, and

ofgroundwaterinaquifers.

For a rock to be considered as an exploitable hydrocarbon reservoir

without stimulation, its permeability must be greater than

approximately 100 mD (depending on the nature of the hydrocarbon -

gas reservoirs with lower permeabilities are still exploitable because of

the lowerviscosityof gas with respect to oil). Rocks with

permeabilities significantly lower than 100 mD can form

efficientseals (seepetroleum geology). Unconsolidated sands may

have permeabilities of over 5000 mD.

The concept has also many practical applications outside of geology,

for example inchemical engineering(e.g.,filtration).
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[edit]Description

Permeability is part of the proportionality constant inDarcy's law which

relates discharge (flow rate) and fluid physical properties

(e.g.viscosity), to a pressure gradient applied to the porous media:

Therefore:

where:

is thesuperficial fluid flow velocitythrough the medium (i.e.,the average velocity calculated as if the fluid were the

onlyphasepresent in the porous medium) (m/s)

is the permeability of a medium (m2)

is the dynamicviscosityof the fluid (Pas)

is the appliedpressuredifference (Pa)

is the thickness of the bed of the porous medium (m)

In naturally occurring materials, permeability

values range over many orders of magnitude (seetable below for an example of this range).

[edit]Relation to hydraulicconductivity

The proportionality constant specifically for the

flow of water through a porous media is called

thehydraulic conductivity; permeability is a

portion of this, and is a property of the porous

media only, not the fluid. Given the value of

hydraulic conductivity for a subsurface system, ,

the permeability can be calculated as:
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where

is the permeability, m2

is the hydraulic conductivity, m/s

is the dynamic viscosity, kg/(ms) is the density of the fluid, kg/m

3

is the acceleration due to gravity, m/s2.

[edit]Determination

Permeability is typically determined in the lab

by application ofDarcy's lawunder steady

state conditions or, more generally, by

application of various solutions to thediffusionequationfor unsteady flow conditions.[1]

Permeability needs to be measured, either

directly (usingDarcy's law), or

throughestimationusingempiricallyderived

formulas. However, for some simple models of

porous media, permeability can be calculated

(e.g.,random close packing of identical

spheres).

[edit]Permeability model based onconduit flow

Based onHagenPoiseuille equationfor

viscous flow in a pipe, permeability can be

expressed as:

where:is the intrinsic permeability [length

2]

is a dimensionless constant that is related to the configuration

of the flow-paths

is the average, or effective porediameter[length].
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[edit]Intrinsic and absolutepermeability

The terms intrinsic

permeabilityand absolute

permeabilitystates that the

permeability value in question is

anintensive property(not a spatial

average of a heterogeneous block

of material), that it is a function of

the material structure only (and not

of the fluid), and explicitly

distinguishes the value from thatofrelative permeability.

[edit]Permeability togases

Sometimes permeability to gases

can be somewhat different that

those for liquids in the same media.

One difference is attributable to"slippage" of gas at the interface

with the solid[2]when the gasmean

free pathis comparable to the pore

size (about 0.01 to 0.1 m at

standard temperature and

pressure). See alsoKnudsen

diffusionandconstrictivity. For

example, measurement ofpermeability through sandstones

and shales yielded values from

9.0x1019 m2 to 2.4x1012 m2 for

water and between 1.7x1017

m2

to

2.6x1012

m2

for nitrogen

gas.[3]Gas permeability ofreservoir
http://en.wikipedia.org/w/index.php?title=Permeability_(earth_sciences)&action=edit&section=7http://en.wikipedia.org/w/index.php?title=Permeability_(earth_sciences)&action=edit&section=7http://en.wikipedia.org/w/index.php?title=Permeability_(earth_sciences)&action=edit&section=7http://en.wikipedia.org/wiki/Intensive_and_extensive_propertieshttp://en.wikipedia.org/wiki/Intensive_and_extensive_propertieshttp://en.wikipedia.org/wiki/Intensive_and_extensive_propertieshttp://en.wikipedia.org/wiki/Relative_permeabilityhttp://en.wikipedia.org/wiki/Relative_permeabilityhttp://en.wikipedia.org/wiki/Relative_permeabilityhttp://en.wikipedia.org/w/index.php?title=Permeability_(earth_sciences)&action=edit&section=8http://en.wikipedia.org/w/index.php?title=Permeability_(earth_sciences)&action=edit&section=8http://en.wikipedia.org/w/index.php?title=Permeability_(earth_sciences)&action=edit&section=8http://en.wikipedia.org/wiki/Permeability_(earth_sciences)#cite_note-1http://en.wikipedia.org/wiki/Permeability_(earth_sciences)#cite_note-1http://en.wikipedia.org/wiki/Mean_free_pathhttp://en.wikipedia.org/wiki/Mean_free_pathhttp://en.wikipedia.org/wiki/Mean_free_pathhttp://en.wikipedia.org/wiki/Mean_free_pathhttp://en.wikipedia.org/wiki/Knudsen_diffusionhttp://en.wikipedia.org/wiki/Knudsen_diffusionhttp://en.wikipedia.org/wiki/Knudsen_diffusionhttp://en.wikipedia.org/wiki/Knudsen_diffusionhttp://en.wikipedia.org/wiki/Constrictivityhttp://en.wikipedia.org/wiki/Constrictivityhttp://en.wikipedia.org/wiki/Constrictivityhttp://en.wikipedia.org/wiki/Permeability_(earth_sciences)#cite_note-2http://en.wikipedia.org/wiki/Permeability_(earth_sciences)#cite_note-2http://en.wikipedia.org/wiki/Permeability_(earth_sciences)#cite_note-2http://en.wikipedia.org/wiki/Reservoir_rockhttp://en.wikipedia.org/wiki/Reservoir_rockhttp://en.wikipedia.org/wiki/Reservoir_rockhttp://en.wikipedia.org/wiki/Permeability_(earth_sciences)#cite_note-2http://en.wikipedia.org/wiki/Constrictivityhttp://en.wikipedia.org/wiki/Knudsen_diffusionhttp://en.wikipedia.org/wiki/Knudsen_diffusionhttp://en.wikipedia.org/wiki/Mean_free_pathhttp://en.wikipedia.org/wiki/Mean_free_pathhttp://en.wikipedia.org/wiki/Permeability_(earth_sciences)#cite_note-1http://en.wikipedia.org/w/index.php?title=Permeability_(earth_sciences)&action=edit&section=8http://en.wikipedia.org/wiki/Relative_permeabilityhttp://en.wikipedia.org/wiki/Intensive_and_extensive_propertieshttp://en.wikipedia.org/w/index.php?title=Permeability_(earth_sciences)&action=edit&section=7


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rockandsource rockis important

inpetroleum engineering, when

considering the optimal extraction

ofshale gas,tight gas, orcoalbed

methane.

[edit]Tensor permeability

To model permeability

inanisotropicmedia, a

permeabilitytensoris needed.

Pressure can be applied in three

directions, and for each direction,

permeability can be measured (viaDarcy's law in 3D) in three

directions, thus leading to a 3 by 3

tensor. The tensor is realized using

a 3 by 3matrixbeing

bothsymmetricandpositive

definite(SPD matrix):

The tensor is symmetric by

theOnsager reciprocal relations. The tensor is positive definite as

the component of the

flowparallelto the pressure drop

is always in the same direction

as the pressure drop.

The permeability tensor is

alwaysdiagonalizable(being both

symmetric and positive definite).Theeigenvectorswill yield the

principal directions of flow,

meaning the directions where flow

is parallel to the pressure drop, and
http://en.wikipedia.org/wiki/Reservoir_rockhttp://en.wikipedia.org/wiki/Reservoir_rockhttp://en.wikipedia.org/wiki/Source_rockhttp://en.wikipedia.org/wiki/Source_rockhttp://en.wikipedia.org/wiki/Source_rockhttp://en.wikipedia.org/wiki/Petroleum_engineeringhttp://en.wikipedia.org/wiki/Petroleum_engineeringhttp://en.wikipedia.org/wiki/Petroleum_engineeringhttp://en.wikipedia.org/wiki/Shale_gashttp://en.wikipedia.org/wiki/Shale_gashttp://en.wikipedia.org/wiki/Shale_gashttp://en.wikipedia.org/wiki/Tight_gashttp://en.wikipedia.org/wiki/Tight_gashttp://en.wikipedia.org/wiki/Tight_gashttp://en.wikipedia.org/wiki/Coalbed_methanehttp://en.wikipedia.org/wiki/Coalbed_methanehttp://en.wikipedia.org/wiki/Coalbed_methanehttp://en.wikipedia.org/wiki/Coalbed_methanehttp://en.wikipedia.org/w/index.php?title=Permeability_(earth_sciences)&action=edit&section=9http://en.wikipedia.org/w/index.php?title=Permeability_(earth_sciences)&action=edit&section=9http://en.wikipedia.org/w/index.php?title=Permeability_(earth_sciences)&action=edit&section=9http://en.wikipedia.org/wiki/Anisotropichttp://en.wikipedia.org/wiki/Anisotropichttp://en.wikipedia.org/wiki/Anisotropichttp://en.wikipedia.org/wiki/Tensorhttp://en.wikipedia.org/wiki/Tensorhttp://en.wikipedia.org/wiki/Tensorhttp://en.wikipedia.org/wiki/Matrix_(mathematics)http://en.wikipedia.org/wiki/Matrix_(mathematics)http://en.wikipedia.org/wiki/Matrix_(mathematics)http://en.wikipedia.org/wiki/Symmetric_matrixhttp://en.wikipedia.org/wiki/Symmetric_matrixhttp://en.wikipedia.org/wiki/Symmetric_matrixhttp://en.wikipedia.org/wiki/Positive-definite_matrixhttp://en.wikipedia.org/wiki/Positive-definite_matrixhttp://en.wikipedia.org/wiki/Positive-definite_matrixhttp://en.wikipedia.org/wiki/Positive-definite_matrixhttp://en.wikipedia.org/wiki/Onsager_reciprocal_relationshttp://en.wikipedia.org/wiki/Onsager_reciprocal_relationshttp://en.wikipedia.org/wiki/Onsager_reciprocal_relationshttp://en.wikipedia.org/wiki/Parallel_(geometry)http://en.wikipedia.org/wiki/Parallel_(geometry)http://en.wikipedia.org/wiki/Parallel_(geometry)http://en.wikipedia.org/wiki/Diagonalizablehttp://en.wikipedia.org/wiki/Diagonalizablehttp://en.wikipedia.org/wiki/Diagonalizablehttp://en.wikipedia.org/wiki/Eigenvectorshttp://en.wikipedia.org/wiki/Eigenvectorshttp://en.wikipedia.org/wiki/Eigenvectorshttp://en.wikipedia.org/wiki/Eigenvectorshttp://en.wikipedia.org/wiki/Diagonalizablehttp://en.wikipedia.org/wiki/Parallel_(geometry)http://en.wikipedia.org/wiki/Onsager_reciprocal_relationshttp://en.wikipedia.org/wiki/Positive-definite_matrixhttp://en.wikipedia.org/wiki/Positive-definite_matrixhttp://en.wikipedia.org/wiki/Symmetric_matrixhttp://en.wikipedia.org/wiki/Matrix_(mathematics)http://en.wikipedia.org/wiki/Tensorhttp://en.wikipedia.org/wiki/Anisotropichttp://en.wikipedia.org/w/index.php?title=Permeability_(earth_sciences)&action=edit&section=9http://en.wikipedia.org/wiki/Coalbed_methanehttp://en.wikipedia.org/wiki/Coalbed_methanehttp://en.wikipedia.org/wiki/Tight_gashttp://en.wikipedia.org/wiki/Shale_gashttp://en.wikipedia.org/wiki/Petroleum_engineeringhttp://en.wikipedia.org/wiki/Source_rockhttp://en.wikipedia.org/wiki/Reservoir_rock


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theeigenvaluesrepresenting the

principal permeabilities.

[edit]Ranges of common

intrinsic permeabilitiesThese values do not depend on the

fluid properties; see the table

derived from the same source for

values ofhydraulic conductivity,

which are specific to the material

through which the fluid is flowing.

Permeability Perviou

UnconsolidatedSand&GravelWell Sorted

Gravel

Unconsolidated Clay &

Organic

Consolidated Rocks Highly Fractur

(cm2) 0.001 0.0001

(millidarcy) 10+8

10+7

Source: modified from Bear, 1972

9. SOIL PERMEABILITY

9.0 Why is it important to determine soil permeability?
http://en.wikipedia.org/wiki/Eigenvalueshttp://en.wikipedia.org/wiki/Eigenvalueshttp://en.wikipedia.org/wiki/Eigenvalueshttp://en.wikipedia.org/w/index.php?title=Permeability_(earth_sciences)&action=edit&section=10http://en.wikipedia.org/w/index.php?title=Permeability_(earth_sciences)&action=edit&section=10http://en.wikipedia.org/w/index.php?title=Permeability_(earth_sciences)&action=edit&section=10http://en.wikipedia.org/wiki/Hydraulic_conductivityhttp://en.wikipedia.org/wiki/Hydraulic_conductivityhttp://en.wikipedia.org/wiki/Hydraulic_conductivityhttp://en.wikipedia.org/wiki/Sandhttp://en.wikipedia.org/wiki/Sandhttp://en.wikipedia.org/wiki/Gravelhttp://en.wikipedia.org/wiki/Gravelhttp://en.wikipedia.org/wiki/Gravelhttp://en.wikipedia.org/wiki/Gravelhttp://en.wikipedia.org/wiki/Sandhttp://en.wikipedia.org/wiki/Hydraulic_conductivityhttp://en.wikipedia.org/w/index.php?title=Permeability_(earth_sciences)&action=edit&section=10http://en.wikipedia.org/wiki/Eigenvalues


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Soil permeability is the property of the soil totransmit water and air and is one of the mostimportant qualities to consider for fish culture.

A pond built in impermeable soil will lose little

water throughseepage.

The more permeable the soil, the greater the

seepage. Some soil is so permeable and

seepage so great that it is not possible to

build a pond without special construction

techniques. You willlearn about these

techniquesin a later volume in this series.

Soils are generally made up oflayers and soil

quality often varies greatly from one layer to

another. Before pond construction, it is

important to determine the relative position of

the permeable and impermeable layers. The

design of a pond should be planned to avoid

having a permeable layer at the bottom to

prevent excessive water loss into the subsoil

by seepage.

The dikes of the pond should be built with soil which will ensure a good water retention. Again,soil quality will have to be checked with this in mind.
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9.1 Which factors affect soil permeability?

Many factors affect soil permeability. Sometimes they are extremely localized, such as cracksand holes, and it is difficult to calculate representative values of permeability from actualmeasurements. A goodstudy of soil profiles provides an essential check on such

measurements. Observations on soil texture, structure, consistency, colour/mottling, layering,visible pores and depth to impermeable layers such as bedrock and claypan* form the basis fordeciding if permeability measurements are likely to be representative.

Note: you have already learned that soil is made up of a number of horizons, each of themusually having different physical and chemical properties. To determine the permeability of soilas a whole, each horizon should be studied separately.

9.2 Soil permeability relates to soil texture and structure

The size of the soil pores is of great importance with regard to the rate of infiltration (movementof water into the soil) and to the rate ofpercolation (movement of water through the soil). Pore

size and the number of pores closely relate to soil texture and structure, and also influence soilpermeability.

Permeabi l i ty var iat ion accord ing to soi l texture

Usually, the finer the soil texture, the slower the permeability, as shown below:

Soil Texture Permeability

Clayey

soilsFine

From very slow to

very rapidLoamy

soils

Moderately fine

Moderately

coarse

Sandy Coarse
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soils

Example

Average permeability for different soil textures in cm/hour

Sand 5.0

Sandy loam 2.5

Loam 1.3

Clay loam 0.8

Sil ty clay 0.25

Clay 0.05

Permeabi l i ty var iation acco rding tosoi l structure

Structure may greatly modify the permeability rates shown above, as follows:

Structure type Permeability

Platy

- Greatly

overlapping

From very slow to

very rapid

- Slightlyoverlapping

Blocky

Prismatic

Granular

1 This may vary according to the degree to which the structure is developed.

It is common practice to alter the soil structure to reduce permeability, for example, in irrigatedagriculture through thepuddlingof rice fields and in civil engineering through themechanical compaction* of earthen dams. Similar practices may be applied to fish-ponds toreduce water seepage.

9.3 Soil permeability classes
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Permeability is commonly measured in termsof the rate of water flow through the soil in agiven period of time. It is usually expressedeither as a permeability rate in centimetresper hour (cm/h), millimetres per hour (mm/h),

or centimetres per day (cm/d), or asacoefficient of permeability k in metres persecond (m/s) or in centimetres per second(cm/s).

Example

For agriculture and conservationuses, soil permeability classes are based on permeability rates,andfor civil engineering, soil permeability classes are based on the coefficient of permeability(see Tables 15 and 16).

Forfish culture, two methods are generally used to determine soil permeability. They are:

The coefficient of permeability;

The seepage rate.

For the siting of ponds and the construction of dikes, the coefficient of permeability is generallyused to qualify the suitability of a particular soil horizon:

Dikes without any impermeable clay core may be built from soils having a coefficient ofpermeability less thanK = 1 x 10

-4m/s;

Pond bottoms may be built into soils having a coefficient of permeability less than K = 5 x 10-

6m/s.

Forpond management, the seepage rate is generally used:

In commercial pond culture, an average seepage rate of 1 to 2 cm/d is considered acceptable,but corrective measures should be taken to reduce soil permeability when higher values exist,particularly when they reach 10 cm/d or more.

9.4 Measurement of soil permeability in the laboratory
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When you take an undisturbed sample to a testing laboratory, to measure permeability, acolumn of soil is placed under specific conditions such as water saturation and constant head ofwater. The result will be given to you either as a permeability rate (see Table 15), or asacoefficient of permeability (see Table 16).

TABLE 15

Soil permeability classes for agriculture and

conservation

Soil permeability

classes

Permeability rates1

cm/hour cm/day

Very slowLess than

0.13Less than 3

Slow 0.13 - 0.3 3 - 12

Moderately slow 0.5 - 2.0 12 - 48

Moderate 2.0 - 6.3 48 - 151

Moderately rapid 6.3 - 12.7 151 - 305

Rapid 12.7 - 25 305 - 600

Very rapidMore than

25

More than

600

1Saturated samples under a constant water

head of 1.27 cm

TABLE 16

Soil permeability classes for civil engineering

Soil permeability

classes

Coefficient of

permeability (K in

m/s)

Lower

limit

Upper

limit

Permeable 2 x 10-7 2 x 10-1

Semi-permeable 1 x 10-11 1 x 10-5

Impermeable 1 x 10-11 5 x 10-7

9.5 Measurement of soil permeability in the field

To measure soil permeability in the field, you can use one of the following tests:

The visual evaluation of the permeability rate of soil horizons;

A simple field test for estimating soil permeability;

A more precise field test measuring permeability rates.

The visual evaluat ion o f the perm eabi li ty rate of soi l h or izons

The permeability of individual soil horizons may be evaluated by the visual study of particularsoil characteristics which have been shown by soil scientists to be closely related to


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permeability classes. The most significant factor in evaluating permeability is structure: its type,grade, and aggregation characteristics, such as the relationship between the length of horizontaland vertical axes of the aggregates and the direction and amount of overlap.

Although neithersoil texture norcolour mottlingalone are reliable clues, these soil propertiesmay help to estimate permeability when considered together with the structural

characteristics. To evaluate visually the permeability of soil horizons:

Examine a fresh soil profile in an open pit;

Determine the soil horizons present;

UsingTable 17A, evaluate the permeability class to which each horizon belongs, carefullystudying the structural characteristics of the soil;

Confirm your results through the other soil properties shown inTable 17B;

Ranges of permeability rates may then be found in Table 15.

TABLE 17A

Visual indicators of permeability: structural characteristics of soil
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TABLE 17 B

Visual Indicators of permeability: texture, physical behaviour and colour of soil

A s imple f ield test for est imat ing soi l permeabi l i ty

Dig a hole as deep as your waist; Early in the morning, fill it with water to the

top;


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By the evening, some of the water willhave sunk into the soil;

Fill the hole with water to the top again,and cover it with boards or leafy branches;

If most of the water is still in the hole thenext morning, the soil permeability issuitable to build a fish-pond here;

Repeat this test in several other locationsas many times as necessary, according tothe soil quality.

A m ore precise f ield test for m easur ing permeabi l i ty rates

Carefully examine the drawings you havemade when studying your soil profiles;

On the basis of texture and structure,determine which soil horizons seem to have


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Note: you could also use the visual method(seeTables 17Aand17B) to estimatepermeability.

the slowest permeability;

Mark the soil horizons on your drawings

which seem to have the slowestpermeability. Use a coloured pencil;

Note: water seeps into the soil bothhorizontally and vertically, but you need onlybe concerned with the vertical water seepagebecause this is mainly what happens inponds.

Dig a hole approximately 30 cm in

diameter until you reach the uppermostleast permeable horizon;

Thoroughly smear the sides of the hole

with heavy wet clay or line them with aplastic sheet, if available, to make themwaterproof;

Pour water into the hole to a level of about10 cm;

At first, the water will seep down rather quickly, and you will have to refill as it disappears. Whenthe pores of the soil are full of water, seepage will slow down. You are then ready to measure thepermeability of the soil horizon at the bottom of the hole;
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Make sure that the water in the hole isabout 10 cm deep as before. If it is not,add water to reach that level;

Put a measuring stick into the water andrecord the exact water depth, inmillimetres (mm);

Check the water level in the hole everyhour for several hours. Record the rate ofseepage for each hourly period. If thewater disappears too rapidly, add water tobring the level up to 10 cm again.Measure the water depth very carefully;


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When your hourly measurements becomenearly the same, the rate of permeability isconstant and you may stop measuring;

If there are great differences in seepageeach hour, continue pouring water into thehole to keep the level at 10 cm until the

rate of seepage remains nearly the same;

Note: a soil horizon with suitable permeabilityfor a pond bottom should also be at least 0.7-1 m thick, unless lower horizons exist withsuitable permeability and thickness.

Now compare your results with thefollowing values:

Permeabi l i ty rate

in mm/hSui tab i l i ty of hor izon for a pond bottom

Slower than 2 Acceptable seepage: soil suitable

2-5Fast seepage: soil suitable ONLY if seepage due to soil structure

which will disappear when pond is filled

5-20Excessive seepage: soil unsuitable unless seepage can be reduced

as described below

If the permeability rate is faster than 5 mm/h , this may be owing to a strongly developed structurein the soil. In such cases, you try to reduce the permeability rate by destroying the structure, asfollows:

Puddle the bottom soil of the hole as deepas you can;

Repeat the more precise permeability testuntil you can measure a nearly constantvalue for seepage.


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If this new permeability rate does not exceed 4 mm/h, you may consider this soil horizon assuitable for a pond bottom. However, the entire bottom of the pond will have to be puddled beforefilling it with water;

If this new permeability rate exceeds 4 mm/h, this may be owing to the presence of a permeable

soil horizon under the horizon you have tested. Such a permeable layer is often found betweenlayers of soil which are semi- permeable or even impermeable;

Check this with the following test

Dig a new hole 30 cm in diameterthrough the uppermost least permeable

layer (A) to the to p of th e next least

permeable layer (B);

Repeat the permeabi l i ty test u nti l youmeasure a nearly constant value for

seepage;

I f this permeabi l i ty rate does notexceed 3 mm /h, you may cons ider th is

soi l hor izon as sui tab le for a pond

bottom. However, remember that s uch

slow permeabi l ity should be found in a

layer at least 0.7-1 rn thic k to ensure

l imi ted seepage through the pond

bo t tom.

Note: when building your pond, you do not necessarily need to remove a shallow permeablelayer if there is a deeper layer of soil which is not permeable and will serve to hold the water.You must, however, build the pond dikes down to the deeper non-permeable layer to form an

enclosed basin and to avoid horizontal water seepage (see Section 9.0).

9.6 Determining coefficients of permeability

To obtain a more accurate measurement of soil permeability, you can perform the following testin the field which will give you a value for the coefficient of permeability:

Using a bucket auger, drill a hole about 1m deep in the soil at the location whereyou wish to determine the coefficient ofpermeability;

Fill the hole with water to the top;
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Every five minutes, for at least 20 minutes,refill the hole to the top to be sure that thesoil is fully saturated;

Top the water in the hole and start measuringthe rate at which the water surface goes

down, using a watch to measure time and acentimetre-graduated ruler to measure thedistance P between the water surface andthe top of the hole. Stop measuring when therate becomes nearly constant;

Example

Rate becomes constant

Measure exactly the total depth of the hole (H) and its diameter (D). Express all measurementsin metres (m): for example

H = 1.15 m and D = 12 cm or 0.12 m

For each of the above two consecutive measurements of time/distance, calculate the coefficientof permeability K using the following formula:

K= (D2) x In (h1 h2) / 2 (t2- t1)

wh ere (D 2) is the radius of t he hole or half i ts diameter in metres;In re fers to theNapierian ornatural logarithm;h1and h2are the two co nsecutiv e depths of water in metres, h1at the start and h2at the end of th e

time interval ;

(t2- t1) ex p res ses the t im e in ter val between two consec u t iv e measurem en ts , in seconds ;

Note: the h-values may be readily calculated as the differences between the total depth of thehole H and the successive P values. Be careful to express all the measurements in metres andseconds so as to obtain K in m/s.


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Now compare your K values (in m/s) with those inTable 16.

Example

I f (D 2) = 0.12 m 2 = 0.06 m and H = 1.15 m, calculations of th e various K v alues are made

progressive ly accord ing to the formula (seeTable 18).

Note: for obtaining the natural logarithm of (h1 h2), you will have to use either a logarithmictable or a pocket calculator.

Remember that 10 - 6 = 0.000001 and 6.8 x 10-6 = 0.0000068, the negative exponent of 10reflecting the decimal place to be given to the multiplicant.

If you wish to compare a K value (m/s) with permeability rates (cm/day) , multiply K by 8 640 000or 864 x 104 such as for example:

K = 1 x 10-5

m/s = 86.4 cm/day

TABLE 18

Successive steps for the calculation of coefficients of permeability on the basis of field

measurements

(for a test hole with H = 1.15 m and D = 0.12 m)

NOTE: The formula for calculating coefficients of permeability is K = [(D 2) x In (h 1 h2)] / 2(t2 - t1)

or A B (see Section 9.6).

Hydraulic conductivityFrom Wikipedia, the free encyclopedia

Hydraulic conductivity, symbolically represented as , is a property of vascular plants, soil or rock, that
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describes the ease with which water can move through pore spaces or fractures. It depends on the intrinsic

permeabilityof the material and on the degree of saturation. Saturated hydraulic conductivity, Ksat, describes

water movement through saturated media.
http://en.wikipedia.org/wiki/Intrinsic_permeabilityhttp://en.wikipedia.org/wiki/Intrinsic_permeabilityhttp://en.wikipedia.org/wiki/Intrinsic_permeabilityhttp://en.wikipedia.org/wiki/Intrinsic_permeabilityhttp://en.wikipedia.org/wiki/Intrinsic_permeabilityhttp://en.wikipedia.org/wiki/Intrinsic_permeability

soil compaction tests

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