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Relative

This document provides instructions for determining the relative density of a cohesionless soil through a simple laboratory test. It defines relative density as the fraction of the difference between a soil's loosest and densest possible void ratios compared to its natural state. The test involves obtaining the maximum and minimum unit weights of a soil sample through mechanical vibration compaction and by allowing the material to fall through water, respectively. The relative density value provides information about a cohesionless soil's state compared to its loosest and densest possible conditions.

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54 views2 pages

Relative

This document provides instructions for determining the relative density of a cohesionless soil through a simple laboratory test. It defines relative density as the fraction of the difference between a soil's loosest and densest possible void ratios compared to its natural state. The test involves obtaining the maximum and minimum unit weights of a soil sample through mechanical vibration compaction and by allowing the material to fall through water, respectively. The relative density value provides information about a cohesionless soil's state compared to its loosest and densest possible conditions.

Uploaded by

عمر بحيصي
Copyright
© © All Rights Reserved
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:References

ASTM(1973)Relative Density Involving Cohesionless Soils

Opjective
To determine the state of a cohesionless soil with respect to its
maximum and minimum densities .and to introduced to the
limitations of this type of test.The student will be also
introduced to a simple method of obtaining a compaction
.density for a cohesionless soil
Equipment

Standard compaction mold or a calibrated volume measure as


.used in concretemix design laboratories
.Hand or mechanical vibration equipment

General Discussion
Relative density Dr of the soil.Defined by Terzaghi as a fraction
equation of void ratios of the soil in its loosest state (e max),in
.the natural soil state (e),and in the densest possible state (e min)

Dr =e max-e

It is often more convenient,however,to use the unit weight of


the soil since the void-ratio computation requires the use of the
specific gravity of the soil,which may not be known.Using the
unit weights of the soil,the relative density can be expressed as

Dr =yf –y1 y2
Y2-y1 yf

Where yf =density of the soil in its natural state (field value)


Y2 =densest value of unit weight obtained in the
laboratory
Y1 =loosest value of unit weight obtained in the laboratory
The problems in this test occur from properly defining the soil
in its loosest and most dense states.As a consequence,some
laboratories use a mechanical vibration device,and under an
arbitrarily selected confining pressure and length of time of
vibration,the soil is defined as being in the most dense
state.Alternatively,vibrating a saturated soil has been used to
.obtain an arbitrary maximum density
The loosest state has also been arbitrarily obtained by allowing
.the material to fall through water to form a specified volume
The term relative density hs no particular significance for

cohesive soil.For these materials,consistenc(i.e., soft,medium


stiff,stiff,hard,etc.)and unit weight are generally used to describe
.the soil state

Procedure
Each individual should take a representative sample of the .1
oven-dry cohesionless soil from the stock supply furnished.Be
.sure to break any remaining lumps prior to use
Obtain a standard compaction mold.Use the same mold for .2
both the maximum and minimum-density determination so that
you do not have to obtain mold dimensions and compute the
.volume
Make three trails of maximum density by placing the material .3
in the standard mold in five layers,confining the layer with a
round steel block of at least 12kg or obtain the assistance of
.another student to confine the soil using the confining plate
Next,using the same soil and mold carefully pour the material .4
into the mold,distributing the soil in a circular motion over the
mold.Slightly overfill,then with a straightedge strike the excess
with as little vibration as possible.Obtainthe test weight and
.repeat at least two more times
Use the smallest density obtained for the minimum density of
the soil.Put this value on the blackboard beside your maximum
density.Be sure to identify your work so the instructor will know
.who has not completed the assignment

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