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4 SOIL DENSITY AND COMPACTION
Density of a soil provides a measure of the quantity of materials (mass) it contains
related to the amountof space (volume) the materials occupy. The volume here refers
to the volume of soil solid grains plusthe volume of voids between grains. [Refer toChapter 2 for various states of soil density and the related equations (i.e. bulk density
(b), dry density (d), saturated density (sat), submerged density (sub)].
In general, the higher its density value, the denser or more compacted the soil is.
4.1 Relative Density
The actual void ratio of a soil lies somewhere between the possible minimum and
maximum values, i.e. emin and emax. In the case of soils without fines (sometimesreferred to as cohesionless, i.e., sands and gravels), a more convenient measure of the
state of compaction is provided by indicating the relationship between the actual void
ratio, e and the two extremes emin and emax that these soils can attain. Such an
indication is termed the Density Index (Id) or sometimes referred to as Relative
Density (DR).
minmax
max
ee
eeId
=
where e is the current voids ratio,
emax, eminare the maximum and minimum voids ratios measured in the laboratory fromStandard Tests. (See appendix 1 for determination of emaxand emin.)
Note that if e = emin, Id= 1 and the soil is in its densest state
e = emax, Id= 0 and the soil is in its loosest state
Table 3.1 Relative Compaction States for cohesionless soils
Density 0-15 15-35 35-65 65-85 85-100
Index (%)State of Very loose Loose Medium Dense Very Dense
Compaction
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The expression for Density Index can also be written in terms of the dry density associated
with the various voids ratios. From the definitions we have
1=d
wsG
e
and hence
)(
)(
11
11
minmax
minmax
maxmin
min
ddd
ddd
dd
yd
dI
=
=
Note that you cannot determine the density from knowing Id. This is because the values of the
maximum and minimum dry densities (void ratios) can vary significantly. They depend onsoil type (mineralogy), the particle grading, and the angularity.
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CHAPTER 4SOIL MECHANICS AND GEOLOGY
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Appendix 1
Determination of emaxand emin
Determination of emax
place a mould (mass = M1 and volume = V1) under water and quickly pour soil intoit from just above the top
strike off level the soil surface and determine the mass of mould+water+soil (M2)
sat(min) =M - M
V
2 1
1
=(Gs + e )
1 + e
max w
max
e =G -
-max
s sat (min)
sat (min) w
w
and n =e
1 + emax
max
max
Determination of emin
place a standard compaction mould (mass = M3and volume =V3) under water
place the soil in the mould in three layers of approximately equal thickness, each ofthe layer is compacted using a vibrating hammer
strike off level the soil surface and determine the mass of mould+soil+water (M4)
sat(max) =
M - M
V
4 3
3 =
( + e
1 + e
min w
min
Gs )
e =G -
-min
s sat (max)
sat (max) w
w and n =
e
1 + emin
min
min
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CHAPTER 4SOIL MECHANICS AND GEOLOGY
Pour soil into
the mould
Compact the soil in the
mould in three layers
using a vibrating hammer
1
2
3
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4.2 Field Measurement of Soil Density
4.2.1 Sand Rreplacement Method (Sand Pouring Cylinder Method)
For cohesionless soils, theSand Replacement Method is usedFigure 4.1.
Figure 4.1 Sand Pouring Cylinder
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Equipment (see Figure 4.1):
A pouring cylinder filled to within 15 mm of the top with uniform fine standardsand with diameter of grains between 0.3 mm to 0.6 mm. (The cylinder should
have a shutter to allow the sand to fall through into the cone-shaped space.)
Tool for excavating holes in ground, consisting of a steel dipper and spoon, and ascraper for making the ground level.
A metal tray about 300 mm square with a hole in the centre, 100 mm in diameter
A glass plate
A calibrating container 100 mm in diameter and 150 mm deep
The procedures involves digging a hole in the ground and removing a known mass of
soil from the hole, and filling the hole with standard sand of known density. The
volume of the hole can then be calculated from the mass of the replacing standard sand
used (since the sand density is known). Knowing the volume of the hole and the massof soil removed, the bulk density can be calculated. The dry density can also be
calculated after obtaining the water content.
Test Procedures
Detailed test details are described below:
Calibration of Density of Standard Sand
Step 1: Determine the mass of the cone of sand formed on the glass plate (Figure 4.2).
Make several determinations and take the mean value.
Determine the volume of the calibrating container (Vc) by measuring its dimension,or by filling it with water (the volume of the container is equal to the mass of water
required to fill the container divided by the density of water).
Figure 4.2 Measuring Mass of Sand Cone on Glass Plate
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Step2:
Fill the calibrating container with sand from the pouring cylinder (Figure 4.3). Themass of sand filling the container is found by subtracting the mass of sand in the
cone. This calibration is repeated several times and the mean value is taken.
From the mass of sand filling the calibrating container and the volume of thecalibrating container, the density of the standard sand is determined.
Figure 4.3 Filling the Calibrating Cylinder
Field Test
Step 3:
The test area is scraped level and the metal tray with the central hole is placed onthe levelled area.
A hole in the ground with the same diameter as the hole in the tray is dug to adepth of 150 mm. The excavated soil is placed in a sealed container immediately
and is taken to the laboratory where it is weighed and the moisture contained
determined.
The pouring cylinder, which is filled to within 15 mm of the top with standard sand,is placed on the template over the excavated hole. The shutter is opened and the
sand is allowed to fill the excavated hole (Figure 4.4). By difference, the mass of
standard sand filling the excavated hole can be found.
Figure 4.4 Filling Excavated Hole in Soil
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,h!W {
SOIL MECHANICS AND GEOLOGY
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Calculation:
(a) mass of sand to fill calibrating cylinder (ma):
ma = m1 - m2 - m3
where m1= mass of cylinder and sand before pouring into calibration container
m2= mass of sand in the cone
m3= mass of the cylinder and sand after pouring into the calibration container
(b) the bulk density of the standard sand (sand) is calculated by:
sand = ma/ Va
where Va= the volume of the calibrating container
(c) the mass of sand required to fill the excavated hole (mb) is calculated by:
mb = m4 - m5 - m2
where m4= mass of cylinder and sand before pouring into the excavated hole
m5= mass of cylinder and sand after pouring into the excavated hole
(d) the bulk density of the soil (b) is calculated by:
b = (mt/mb) x sand
where mt= mass of soil (total mass) excavated
mb= mass of sand required to fill the excavated hole
(e) the dry density (d) is calculated by:
d = b/ (1 + w) or d = (md/ mb) x sand
where w= moisture content
md= mass of dry soil excavated
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Ans: sand=1258 kg/m3
SOIL MECHANICS AND GEOLOGY
Ans: bulk density of soil specimen=1134 kg/m3 ; w = 34.4%
d= 844 kg/m 3
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Ans: bulk density of soil specimen=1374 kg/m3 ; w = 34.4%
d= 1022 kg/m3
Ans: sand=1259 kg/m3
SOIL MECHANICS AND GEOLOGY
Mass of soil excavated from hole
w = Mw/Ms = (2.03-1.51)/1.51 x 100%=34.4%
d = b / (1+w)
= 1374/(1 + 34.4%)= 1022 kg/m3
Not to be included inthe notes for Students
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4.2.2 Core Cutter Method
For cohesive soils, theCore cutter method is used (Figure 4.5).
drive a steel cylinder (of known weight and volume), with a hardenedcutting edge, into the ground using a steel rammer and protective dolly
dug out the cutter and trim the soil flush at each end
weigh the whole cylinder with soil to determine the mass of the soil and itsbulk density
if the water content is also determined, the dry density can also be calculated
Figure 4.6 Core Cutter
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Cone
Cone
Cone Cutter
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4.2.3 Nuclear Method
In this method, both the bulk density and water content may be determined
simultaneously. The method is quick and non-destructive. There are variations in this
method depending on the depth of the soil to be measured. The apparatus (Figure 4.7)
consists of a portable box with two radio-active sources at its base. One source emits
gamma rays for density measurement and the other emits fast-moving neutrons for
moisture content measurement. Dense soil absorbs more radiation than loose soil and
the readings reflect overall density. Water content can also be read, all within a few
minutes.
Figure 4.7 Nuclear Meter
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SOIL MECHANICS AND GEOLOGY
Nuclear Gauge Moistureand Density testing
Method
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Procedures
Measuring Density
Position the box well seated on ground to minimize air gaps at the soil interface. Emitted gamma rays penetrate the soil and are reflected back (back scatter). Theintensity of the back scatter varies directly with the density of the soil.
Geiger-Muller tubes detect the scatter and translate the count-rate or intensity ofdetected radiation into a direct reading showing the soil density in kg/m
3. (Using
standard blocks, the Geiger-Muller tubes are precalibrated, the typical range
covered by the meter is 1,100 to 2,700 kg/m3.)
The meter is calibrated in the laboratory by using several materials, such aslimestone and granite grains, which are made into blocks with different densities
that fall within the ranges expected for the soil to be tested. The meter is adjusted
so that the density reading corresponding with the known density of the standardblocks.
Measuring Moisture Content
Fast-moving neutrons from a source at the base of the instrument penetrate the soil.
Collision of the fast-moving neutrons with the hydrogen ions in soil water has theeffect of slowing the neutrons down more effectively than collision with heavier
atoms in the soil.
The intensity of the back scatter of slow-moving neutrons is directly related to thehydrogen concentration and therefore the water content of the soil.
A boron-trifluoride-coated tube, which is a slow neutron detector, is used to detectthe reflected neutrons.
The neutron count-rate is translated directly by the meter into water content inkilograms per cubic meter (kg/m
3) over a range usually of 0 - 800 kg/m
3.
The instrument is pre-calibrated with samples of known water content.
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4.3 COMPACTION OF SOIL
4.3.1 What is compaction?
A simple ground improvement technique, where the soil is made dense through
external mechanical compactive effort.
Whatare done to the soil in compaction?
Solid gains are brought closer together, therefore, soil is denser Decrease in air void volume only
Nochange in water volume
air
water
soilsolid
air
water
soilsolid
+ WATER =+ WATER =
Compactive
Effort
Before Addition ofCompactive
Effort
After
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4.3.2 Why is compaction done? (Purposes)
To increase the shear strengthand therefore the bearing capacityof the soil.
To make the soil less susceptible to subsequent volume changes and therefore
less settlementunder load or under the influence of vibration. To reduce the void ratio of the soil such that the soil will absorb less water(water is no good to fine-grained soil).
Reduction in the void ratio also decreases the permeabilityof the soil (waternot easy to go through).
Compaction can prevent the build up of large water pressuresthat cause soilto liquefy during earthquakes
4.3.3 How is compaction done?
By Pressure (adding load on the soil)
By Vibration (shaking the soil)
By Impact (pounding the soil)
Dynamic Compaction (dropping heavy weights onto the soil)
Vibroflotation
4.3.4 What factors affect the effectiveness of compaction?
the nature and type of soil (i.e., sand or clay, uniform or well graded, plastic ornon-plastic)
the moisture content at the time of placing of soil
the type of compaction plant used
the maximum possible state of compaction attainable for the soil
the maximum amount of compaction effort attainable under field conditions
4.3.5 Laboratory compaction tests
The laboratory compaction test is done to:
assess the suitabilityof the soil for the proposed purposes
assess the acceptabilityof field compaction work (as a field compaction control)
There are several types of test which can be used to study the compactive properties of
soils. Because of the importance of compaction in most earth works standard
procedures have been developed. These generally involve compacting soil into a
mould at various moisture contents. One of the three standard laboratory tests shown
in Table 4.2 is used for this purpose (the most common one is the Proctor test).
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Table 4.2 Standard Laboratory Compaction Tests
Proctor Test Modified AASHTO Test Vibrating Hammer
BS Desigation 2.5 kg method 4.5 kg method Vibrating Hammer
Soil: quantity 5 kg 5 kg 25 kg
Size 20 mm 20 mm 37.5 mm
Hammer:(Mass) 2.5 kg 4.5 kg --
(Face dia.) 50 mm 50 mm --
(Drop) 300 mm 450 mm --
Mould: (Volume) 1000 cm3 1000 cm3 2305 cm3
(Internal dia.) 105 mm 105 mm 152 mm
(Height) 115.5 mm 115.5 mm 127 mm
No. of layers: 3 5 3
No. of blows: 27 27 Vibrated for 60 s
Energy/Force 600 kN/m3 2700 kN/m3 300-400 N
Figure 4.8 Standard Proctor Mold
collar (mould
extension)
Cylindrical
soil mould
Metal guide to control
drop of hammer
Hammer for
compacting soil
Handle
Base plate
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Mould
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4.3.6 Presentation of laboratory compaction test results
To assess the degree of compaction it is important to use the dry density, d, because
we are interested in the mass of solid soil particles in a given volume, not the total
mass per unit volume (which is the bulk density). From the relationships derived
previously we have:
)1()1(
wV
wM
V
wMM
V
MM
V
Md
T
S
T
SS
T
wS
T
T
b ==+
=+
=+
==
Hence, )1( wb
d+
=
where the water content w is in actual value (not %)
This allows us to plot the variation of dry density with water content, giving the typical
response shown in Figure 4.9 below. From this graph we can determine the optimum
water content, wopt, for the maximum dry density, (d)max.
Moisture content
Dryunitwe
ight
mopt
( )max
dry
Figure 4.9 Typical Compaction Test Result
If the soil were to contain a constant percentage, A, of voids containing air where
t
a
vV
VA = (AV in actual value, not %)
writing Vaas VT- Vw- Vswe obtain
wopt
d(max)
Water Content, w
DryDen
sityd
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SOIL MECHANICS AND GEOLOGY
+
Bulk
density
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t
sw
VV
VVA
+=1
then a theoretical relationship between dand w for a given value of AVcan be derived
as follows
)1()(
)1()(
)1(1 wVV
AWW
wV
WW
wws
Vws
T
wsb
d++
+=
+
+=
+=
Nowws
s
sG
MV
= and
w
s
w
w
w
MwMV
==
Hence )1(1
V
s
ws
d A
wG
G
+
=
If the percentage of air voids is zero, that is, the soil is totally saturated, then this
equation becomes
+=
s
ws
dwG
G
1
From this equation we see that there is a limiting dry density for any water content and
this occurs when the voids are full of water. Increasing the water content for asaturated soil will result in a reduction in dry density. The relation between the water
content and dry density for saturated soil is shown on the Figure 4.10. This line is
known as the zero air voids line.
Moisture content
Dryunitweight
zero-air-voidsl
ine
Figure 4.10 Typical compaction curve showing zero-air-voids line
Water Content, w
DryDens
ityd
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SOIL MECHANICS AND GEOLOGY
S+MW (MS+ MW)
1.
2.
soil particles
Gs=2.65
water
air
Ms
tMw
Va
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4.3.7 Effects of water content on compaction
As water is added to a soil (at low water content) it becomes easier for the particles to
move past one another during the application of the compacting forces. As the soil
compacts the voids are reduced and this causes the dry density to increase. Initially, as
the water content increases so does the dry density. However, the increase cannot
occur indefinitely because the soil state approaches the zero air voids line which gives
the maximum dry density for a given water content. Thus as the state approaches the
zero air voids line further water content increases must result in a reduction in dry
density. As the state approaches the zero air voids line a maximum dry density is
reached and the water content at this maximum dry density is called the optimum
water content.
4.3.8 Effects of increasing compactive effort
Increased compactive effort enables greater dry density to be achieved and because of
the shape of the zero air voids line this must occur at a lower optimum water content.
The effect of increasing compactive energy can be seen in Figure 4.11. It should be
noted that for water contents greater than the optimum the use of heavier compaction
machinery will have only a small effect on increasing dry density. For this reason it is
important to have good control over water content during compaction of soil layers in
the field.
Moisture content
Dryunitweight
zero-air-void
sline
increasing c omp activeenergy
Figure 4.11 Effects of compactive effort on compaction curves
It can be seen from this figure that the compaction curve is not a unique soil
characteristic. It depends on the compaction energy. For this reason it is important that
other then giving the values of (d)max and wopt it is important to also specify thecompaction procedure (for example, standard or modified).
DryDensityd
Water Content, w
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Little Increase in the
dry density at the wetsides even thoughincreasing thecompactive effort
than
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4.3.9 Effects of soil type
Table 4.3 below shows typical values for the different soil types obtained from the
Standard Compaction Test.
Table 4.3 Typical compaction results on different soil types.
Typical Values
(d )max (kN/m3) wopt(%)
Well graded sand
SW
22 7
Sandy clay
SWC
19 12
Poorly graded sand
SP
18 15
Low plasticity clay
CL
18 15
Non plastic silt
ML
17 17
High plasticity clay
CH
15 25
It can be seen that compaction is more effective on well-graded soils (compared with
poorly graded) and coarse-grained soils (compared with fine-grained soils).
4.3.10 Field Compression
Compaction by Pressure
This method is used in the field on construction sites and consists of moving heavy
vehicles and plants over loosely-dumped soil to close its void spaces. Different types
of rolling equipment are used in the field according to the nature of the soil and the
weight of plant deemed necessary.
Smooth-wheel roller Pneumatic-tyred roller
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Compaction by Vibration
Compaction by vibrating the soil is usually used in loose granular soils such as sands
and gravels. As the compaction plant vibrated under pressure, the soil densifies and
its void spaces decrease. Various vibratory plants are available, e.g., vibration plate,
vibratory roller, vibratory compactor, vibrotamper.
Compaction by Impact
The ground is pounded by a heavy rammer.
Grid-roller Shee s-foot roller
Vibration plate Vibratory roller
Rammer
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.
Dynamic Compaction
- pounding the ground by a heavy weight
Suitable for granular soils, land fillsand karst terrain with sink holes.
Crater created by the impact
Pounder (Tamper)solution cavities in
limestone
(to be backfilled)
Impact Roller
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Pounder (Tamper)Mass = 5-30 tonneDrop = 10-30 m
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Vibroflotation
holebackfilledwith sand
..andcompacted
vibrator makesa hole in theweak ground
..backfilling andcompactionrepeated untilhole is filled
Vibroflot(vibrating unit)Length = 2 3 mDiameter = 0.3 0.5 mMass = 2 tonnes
Practiced in several forms:
vibrocompaction
stone columns
vibro-replacement
(lowered into the ground
and vibrated)
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Forming the hole.
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SOIL MECGANICS AND GEOLOGY Sept 2009
SOIL DENSIY AND COMPACTION
Page 23 of 27
Backfilling with sand and compact.
CHAPTER 4
Page 25 of 35
SOIL MECHANICS AND GEOLOGYCHAPTER 3
ENGINEERING GEOLOGY AND SOIL MECHANICS
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SOIL MECGANICS AND GEOLOGY Sept 2009
SOIL DENSIY AND COMPACTION
Page 24 of 27
Repeat until hole is filled.
CHAPTER 4
Page 26 of 35
SOIL MECHANICS AND GEOLOGYCHAPTER 3
ENGINEERING GEOLOGY AND SOIL MECHANICS
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SOIL MECGANICS AND GEOLOGY Sept 2009
SOIL DENSIY AND COMPACTION
Page 25 of 27
4.3.11 Field specifications
To control the soil properties of earthwork (e.g. dams, roads) it is usual to specify that
the soil must be compacted to some pre-determined dry unit weight. This specification
is usually that a certain percentage of the maximum dry density, as found from a
laboratory test (Standard or Modified) must be achieved.
For example we could specify that field dry densities must be greater than 98% of the
maximum dry unit weight as determined from the Standard Compaction Test and that
the water content must be a certain amount above or below the optimum. It is then up
to the Contractor to select machinery, the thickness of each lift (layer of soil added)
and to control water contents in order to achieve the specified amount of compaction.
Moisture content
Dryunitweight
(a) (b)
Figure 4.12 Possible field specifications for compaction
The dry density achieved in the field after compaction then must be compared with the
maximum value obtained in the laboratory in order to assess the specified standard.
The required standard may be specified in terms of the relative compaction:
100%xmaximum
achieved=(RC)CompactionRelative
)(
d(field)
labd
Moisture content
Dryunitweight
Accept
Reject
AcceptReject
CHAPTER 4
Page 27 of 35
SOIL MECHANICS AND GEOLOGY
say, 95 or 98% of the Relative Compaction, RC
more stingent fVh
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(8.9)
.
(S-.ll)
'-:
- , It is
desirable
to
have a measure of the spread
of
values which make up the ..
_
sample, and this
is
the basis
of
part b
of
the specification. ,_
-,-_.,--
~ ~ - \
he
oeffi ient
v ri tion
b lch
is
.,.
-''',
C
v
=
standard deviation
of
crushing strengths
s
average crushing strength 1
' ' -
- ~ E X 1)2
The
s t ~ d a r d
deviation s
tI I
where x
=
the ~ i n strength of a sample
1 = the
v r ~ r u s h i n g
strength
of
a batch
n
= the number o f ~ a m p l e s in a batch
For the given data; ~
Sample
s
x
~
c;
1 406 2800
14.5
', ,210.2
2
416
2760
15.1
~ 8 . 0
3
444
2820
15.7
24' 5
4
488 2760
17.6 309.11 -,_
5
483 2760
17.5
3 6
~
:1300.7
1300.7
=
16.13
oot mean square of C
=
.... ......
8 12 Opt imum water
content
of a soil
sample
using
the
standard compaction
test
Describe the standard compaction test, stating its object.
In
a standard compaction [est on a soil
G =
2.70), the following
results were obtained:
Waler comem
ulk
densily
( )
Mg/m
J
5
1.89
8
2.13
10
2.20
12
2.21
15
2.16
20
2.08
Show these results plotted as dry density against water content. On the
same axes, show the zero air voids (saturation) line for the soil.
What are the values
of
void ratio, porosity and degree
of
saturation
for the soil at its condition
of
optimum water content?
IN SITU
TESTS AND
THE
IMPROVEMENT OF SOIL PROPERTIES 245
CHAPTER 3
Further Worked Examples
Page 28 of 35
SOIL MECHANICS AND GEOLOGY ENGINEERING GEOLOGY
AND SOIL MECHANICS
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CHAPTER 3 Further Worked Examples
Page 29 of 35
SOIL MECHANICS AND GEOLOGY
VT
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__
J
V
A
M
A
- 0
V
w
W
M
w
l
V
s
S
M,( P
d
)
for 1
Volumes
sses
Figure 8.16
w
M
w
= 0.10
M
M
w
=
0.10
x
2.00
=
0.2 Mg/m
J
V
0.2
J
w . m
1.0
Using these values, the zero airvoids linehas been plotted on Fig. 8.15, from
which Pd.ma. 2.00
Mg/m
J
and the optimum water content 0.10.
Conside r I m
3
of
the soil
in
this condition.
M
s
2.00 Mg/m
V
s
= 2.00
0.74
mJ
1.00 X 2.7
+
\
: : : : ~ : :
P 200 Mg/m
J
+
~ ~
_ - - - ~ \
:
\
I \
I
Optimum water
J
_ content
10
2.10
2.00
1.90
1.80
1 . 7 0 1 0 L - - - - - : - - - - ~ 1 0 ; - - - - - 7 1 5 < - - - ~ 2 0
w ( )
When [he soil is saturated. A
r
=
0 and the line
is
known as the zero air voids
line
or saturation line.
Figure 8.15
. _ Pw G,
Pd -
I
+ IV G
For the given soil. if
A
r
= 0, since
P
1.0
Mg/m
(8.12)
V
= V
-
V
w
- V
=
I - 0.2 - 0.79
=
0.06
m3
e =
V
v
= V +
V
w
= 0.26 = 0.35
V
s
V
s
0.74
n = V
v
= 0.26 = 0,26
V 1.00
Sr
= V
w
=
2
=
0.77
V
v
0.26
2.7
Pd =
I + 2.7w
Substituting values of IV gives the corresponding values of Pd:
W
d Mg/m
J
)
0.100
2.13
0.125
2.02
0.150
1.92
0.175
1.84
0.200
1.75
8.13 Comparison
of
optimum
water
content
obtaiiiable
i n t he
laboratory
and in the field
The following are the results of a standardcompaction test ona
sandi
cement mixture having an equivalent grain specific gravity
of
2.70:
Water Content )
5
8
1
12.5
20
CO ilpacted dry densiry Mg/m
J
)
1.64
1.78
1.85
1.89
1.84
1.73
Plot these results and on the same axes plot the zero air voids line.
What percentage
of
air voids A
r
)exists in the sample at optimum
water content?
SOLVING PROBLEMS IN SOIL MECHANICS
IN-SII U TESTS
ANO THE
IMPROVEMENT OF SOIL PROPERTIES 245
CHAPTER 3 Further Worked Examples
Page 30 of 35
SOIL MECHANICS AND GEOLOGY
0.74
ENGINEERING GEOLOGY
AND SOIL MECHANICS
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Page 31 of 35
CHAPTER 3 Further Worked ExamplesSOIL MECHANICS AND GEOLOGY
6.4% Air Voids
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Page 32 of 35
CHAPTER 3 Further Worked ExamplesSOIL MECHANICS AND GEOLOGY
Mb
Md
SmallSamples
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Page 33 of 35
CHAPTER 3 Further Worked ExamplesSOIL MECHANICS AND GEOLOGY
useful or not to achieve a higher RC%
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5 ir voids line
\ zero ir voi s line
, .
\
.
\1
+
~ t + Optimum
w ter
~ = > /
I
\ X \ ~
.+
I \\ \ \
. \
2 8
2 6
2 4
M
E
1
2 2
:;
~
;
2
;;;
;;
~
1.98
0
1.98
1.94
1.92
6 7
8 9
10
11 I?
13 14
15
ater ont nt
w )
Figure 8.21
~ o l m s
1
plate bearing tests were carried out on a medium sand. Settlement
o b s e r v ~ ~ s
were subsequently made on two of the actual foundations
at the site
~ i h
were loaded to the same intensity as the plates. The
records
of
the -bservations were:
95
175
Po
5
.5
0.32
Eo)
0.64 1.6 4.8
Sefllemenr
mm
Plot the settlement ratio p Po ag lim; Njle breadth ratio
o
and compare
them with the Terzaghi expression
2 T he readings obtained in a pressure meter test at
in
a clay are shown below. Plot
V
against cell pn:sSIJre\?flO
C om me nt on the result.
256 SOLVING PROBLEMS SOIL MECHANICS
CHAPTER 3 Further Worked Exam les
Page 34 of 35
OIL MECHANICS AND GEOLOGY
Enhancing thecompaction effort canincrease the drydensity obtainablegiven the water contentw at 10%.
ENGINEERING GEOLOGY
AND SOIL MECHANICS
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Chapter 4 Soil Density and Compaction Engineering Geology & Soil Mechanics
Soil Mechanics_Chapter 4_Class Practice_2014
Chapter 4Soil Density and Compaction
Class Practice
Q.1 The maximum and minimum volumes of 1.72 kg of a dry medium sand were
determined in a measuring cup to be 1.21 litresand 0.94 litresrespectively. The
specific gravity of solid grains, Gs, was 2.70 and the density of water was 1000
kg/m3.
(i) Calculate the maximum and minimum dry densities and the void ratio of the
sand at each density state. (5 Marks)
(ii) Determine the dry density of this sand in the field if its relative density was
0.62? (4 Marks)
Q.2 A sand replacement test was performed to determine the in-situ density of the
compacted soil of a fill slope. The test results are summarized below:
Mass of sand in the cone = 0.41 kg
Mass of soil removed from the hole = 1.98 kg
Mass of dry soil after drying completely in the oven = 1.73 kgMass of sand and pouring cylinder before filling the hole = 8.9 kg
Mass of sand and pouring cylinder after filling the hole = 6.82 kg
Density of sand in cylinder = 1540 kg/m3
(i) Find the bulk density and dry density of the compacted soil. (3 marks)
(ii) Determine the in-situ moisture content of the compacted soil. (1 mark)
(iii) If 95% relative compaction is needed and the maximum dry density of the
soil is 1675 kg/m3, will the compaction pass? (2 marks)
Chapter 3
Chapter 3 Soil Density and Compaction
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Chapter 4 Soil Density and Compaction Engineering Geology & Soil Mechanics
Soil Mechanics_Chapter 4_Class Practice_2014
Chapter 4Soil Density and Compaction
Class Practice
Q3. A Standard Proctor compaction tests carried out on a sample of sandy clay and the
following results was obtained:
Bulk Density 2038 2148 2198 2228 2213 2132
(kg/m3)
Moisture 8.5 10.2 11.3 12.6 14.0 15.5
Content (%)
Determine the followings if specific gravity of soil is 2.7:
(i) Tabulate and plot the curve of dry density against moisture content curve.
(13 marks)(ii) Find the maximum dry density and optimum moisture content.
(iii) Find the air void content at its maximum dry density. (2 marks)
(iv) What range of moisture content should be specified in the field for soil
compaction if the required Relative Density is specified to be at least
95%? (2 marks)
Q.4 To investigate the likelihood of liquefaction of a fill slope, the density of the fill soils
was determined. A liquefaction potential was said to exist if the fill failed to attain arelative compaction of 85%. Standard Proctor Test was carried out on samples of the
fill soils excavated from the slope. Results of the tests were tabulated in the following
table.
Bulk Density (kg/m3) 1905 2012 2132 2152 2132
Water Content (%) 11.3 12.5 14.0 15.5 16.8
Gs = 2.70
(i) Calculate the dry density for each test and plot the dry density versus water
content of the fill. On the same graph, plot the dry density/water content curve
for zero air voids ratio. (8 Marks)
(ii) Determine the maximum dry density, optimum water content and the
corresponding air void ratio of the fill. (5 Marks)
(iii) Bulk density of the in-situ fill was 1780 kg/m3with a water content of 13.5%.
Determine whether the fill slope has a liquefaction potential and provide reasons
for the answer. (3 Marks)
Chapter 3 Soil Density and Compaction
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SOIL MECHANICS AND GEOLOGY Sept 2009TUTORIAL 1 Dr. Paul Ho
Page 4 of 4
Q.4 You are given the following laboratory and field test results for a fill.
Laboratory Measurement
Compaction (Proctor) test of the borrowed fill:
Test No. 1 2 3 4 5
Moisture content mor w(%) 12 13 14 16 18
Bulk density b(kg/m3) 1836 1935 2019 2084 2041
Specific gravity Gof soil solid grains of borrowed fill = 2.65
Maximum and Minimum void ratios:
Maximum void ratio emax= 0.87
Minimum void ratio emin= 0.40
Field Measurement
Field density test results of the borrowed fill after compaction :
Field dry density, d: 1730 kg/m3
Field water content, w: 14.5 %
Field Compaction Control Requirements
Relative Compaction RC> 95%wof compacted fill must be within 2 % of wopt
Do the following:
From results of laboratory measurement:
(i) Plot dry densitydagainst wand determine the maximum dry density
d(max)and optimum water content wopt
From results of field measurement:
(ii) The Density Index ID
(iii) The Relative Compaction RC
(iv) Determine if the field dry density satisfies the compaction
requirements.
Soil Density &
Compaction
ENGINEERING GEOLOGY & SOIL MECHANICS
Class Practice
Q.5
Chapter 3 Soil Density and Compaction
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SOIL MECGANICS AND GEOLOGY Sept 2009
SOIL DENSIY AND COMPACTION
Home Exercise
A British Standard compaction test (Proctor test) was conducted on a fill soil
and the following data were collected:
GS= 2.70
Water Content (%) 5 8 10 13 16 19
Bulk Density (kg/m3) 1870 2040 2130 2200 2160 2090
Dry Density (kg/m3)
Dry Density (kg/m3, AV= 0%)
(a) Calculate the dry density for each test and plot the graph of dry density
against water content, and from it determine the maximum dry density
and optimum moisture content.
(b) On the same graph, draw the dry density/water content curve for zero air
voids. Also determine the air void ratio at the maximum dry density.
(c) The fill was then compacted to form a road embankment. A Sand
Pouring Cylinder test was then conducted to measure the dry density ofthe compacted fill with data as follow:
Mass of compacted fill removed from the hole 1.914 kg
Mass of compacted fill after oven drying 1.664 kg
Mass of sand-pouring cylinder before filling the hole with sand 3.426 kg
Mass of sand-pouring cylinder after filling the hole with sand 1.594 kg
Density of pouring sand 1450 kg/m3
Mass of sand in the cone of the sand-pouring cylinder 0.248 kg
The specifications require that the water content may vary above and below the
optimum value by 3 % only and that a Relative Compaction of 97% must be
achieved. Determine therefore if the field compaction satisfied the
specifications.
CHAPTER 4
Ans: w=12%, d =1950kg/m 3
Ans: Ar=4.6%
Ans: No
SOIL MECHANICS AND GEOLOGYENGINEERING GEOLOGY AND SOIL MECHANICS
CHAPTER 3