2_Engineering Geology and Soil Mechanics_Chapter 3_Soil Density and Compaction

7/25/2019 2_Engineering Geology and Soil Mechanics_Chapter 3_Soil Density and Compaction

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SOIL MECGANICS AND GEOLOGY Sept 2009

SOIL DENSIY AND COMPACTION

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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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SOIL MECHANICS AND GEOLOGYENGINEERING GEOLOGY AND SOIL MECHANICS

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3.1


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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

Refer to Chapter 2, page 9/19

ENGINEERING GEOLOGY AND SOIL MECHANICS

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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

Page 3 of 35


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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Re lacement


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3.2

3.2.1


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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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Synopsis


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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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CHAPTER 4

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Ans: sand=1258 kg/m3


Ans: bulk density of soil specimen=1134 kg/m3 ; w = 34.4%

d= 844 kg/m 3


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CHAPTER 4

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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


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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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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+

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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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

CHAPTER 4

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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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Backfilling with sand and compact.

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Repeat until hole is filled.

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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


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

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SOIL MECHANICS AND GEOLOGY ENGINEERING GEOLOGY

AND SOIL MECHANICS


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CHAPTER 3 Further Worked Examples

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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


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


Mb

Md

SmallSamples


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Page 33 of 35


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)



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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



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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


CHAPTER 3

2_Engineering Geology and Soil Mechanics_Chapter 3_Soil Density and Compaction

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