Laboratory Manual GEOTECHNICS · Dry sieve is performed for cohesionless soils if fines are less than 5%. Wet sieve analysis is carried out if fines are more than 5% and of cohesive

“Gheorghe Asachi” Technical University of Iasi

Faculty of Civil Engineering and Building Services

Department of Transportation Infrastructure and Foundations

Laboratory Manual

GEOTECHNICS 2017

Asist.dr.ing.

Florin BEJAN

Geotechnics – Laboratory Manual – Asist.dr.ing. Florin Bejan

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Proper laboratory testing of soils to determine their physical properties is an integral part in

the design and construction of structural foundations, the placement and improvement of soil

properties, and the specification and quality control of soil compaction works. It needs to be

kept in mind that natural soil deposits often exhibit a high degree of nonhomogenity. The

physical properties of a soil deposit can change to a great extent even within a few hundred

feet. The fundamental theoretical and empirical equations that are developed in soil mechanics

can be properly used in practice if, and only if, the physical parameters used in those equations

are properly evaluated in the laboratory. So, learning to perform laboratory tests of soils plays

an important role in the geotechnical engineering profession.


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1. SIEVE ANALYSIS

1.1. AIM

To determine the percentage of various size particles in a soil sample, and to classify the soil.

1.2. APPARATUS

i. Set of sieves of sizes 3 mm, 2 mm, 1 mm, 500 micron, 250 micron, 150 micron, and 63 micron.

ii. Balances of 0.1 g sensivity, along with weights and weight box.

iii. Brush

1.3. THEORY

Soils having particle larger than 0.063 mm size are termed as coarse-grained soils. In these soils, more

than 50% of the total material by mass is larger 63 micron. Coarse grained soil may have boulder,

cobble, gravel and sand.

The following particle classification names are given depending on the size of the particle:

i. BOULDER: particle size is more than 200 mm.

ii. COBBLE: particle size in range 63 mm to 200 mm.

iii. GRAVEL (Gr): particle size in range 2 mm to 63 mm

a. Coarse gravel: 20 to 63 mm.

b. Fine Gravel: 2 mm to 20 mm.

iv. SAND (Sa): particle size in range 0.063 mm to 2 mm.

a. Coarse sand: 0.63 mm to 2 mm.

b. Medium sand: 0.2 mm to 0.63 mm

c. Fine Sand: 0.063 mm to 0.2 mm

Dry sieve is performed for cohesionless soils if fines are less than 5%. Wet sieve analysis is carried out

if fines are more than 5% and of cohesive nature.

In simpler way the particle size distribution curve for coarse grain soil as follows,

Figure 1.1 - The particle size distribution curve for coarse grain soil

Gravels and sands may be either poorly graded (Uniformly graded) or well graded depending on the

value of coefficient of curvature and uniformity coefficient.

Coefficient of curvature (Cc) may be estimated as:


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𝐶𝑐 =𝑑30

2

𝑑10 ∙ 𝑑60

Coefficient of curvature (𝐶𝑐) should lie between 1 and 3 for well grade gravel and sand.

Uniformity coefficient (𝐶𝑢) is given by:

𝐶𝑢 =𝑑60

𝑑10

Its value should be more than 4 for well graded gravel and more than 6 for well graded sand

Where, 𝑑60 = particle size at 60% finer

𝑑30 = particle size at 30% finer

𝑑10 = particle size at 10% finer

1.4. GENERAL COMMENTS

The diameter, 𝑑10 , is generally referred to as effective size. The effective size is used for several

empirical correlations, such as coefficient of permeability. The coefficient of gradation, 𝐶𝑢 , is a

parameter which indicated the range of distribution of grain sizes in a given soil specimen. If 𝐶𝑢 is

relatively large, it indicates a well graded soil. If 𝐶𝑢 is nearly equal to one, it means that the soil grains

are of approximately equal size, and the soil may be referred to as a poorly graded soil.

Figure 1.2 shows the general nature of the grain-size distribution curves for well graded and a poorly

graded soil. In some instances, a soil may have a combination of two or more uniformly graded soil. In

some instances, a soil may have a combination of two or more uniformly graded fractions, and this is

referred to as gap graded. The grain-size distribution curve for a gap graded soil is also shown in Figure

1.2

Figure 1.2 - General nature of grain-size distribution of well graded, poorly graded and gap graded

soil

The parameter 𝐶𝑐 is also referred to as the coefficient of curvature. For sand, if 𝐶𝑐 is greater than 6 and

𝐶𝑐 is between 1 and 3, it is considered well graded. However, for a gravel to be well-graded, 𝐶𝑢 should

be greater than 4 and 𝐶𝑐 must be between 1 and 3.

1.5. PROCEDURE:

i. Weight accurately about 500 g of oven dried soil sample. If the soil has a large fraction

greater than 2.00 mm size, then greater quantity of soil, that is, about 5.0 kg should be taken.

For soil containing some particle greater than 2 mm size, the weight of the soil sample for

grain size analysis should be taken as 0.5 kg to 1.0 kg.


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ii. Clean the sieves and pan with brush and weigh them up to 0.1 g accuracy. Arrange the

sieves in the increasing order of size from top to bottom.

iii. Keep the required quantity of soil sample on the top sieve and shake it with mechanical

sieve shaker for about 5 to 10 minutes. Care should be taken to tightly fit the lid coved on

the top sieve.

iv. After shaking the soil on the sieve shaker, weigh the soil retained on each sieve. The sum of

the retained soil must tally with the original weight of soil taken.

1.6. PRECAUTIONS:

i. During shaking, the lid on the topmost sieve should be kept tight to prevent escape of soils.

ii. While drying the soil, the temperature of the oven should not be more than 105 °C because

higher temperature may cause some permanent change in the 63µ fraction.

1.7. RESULT:

1. The given soil is …………………………..

2. Coefficient of curvature (𝑪𝒄) =

3. Uniformity coefficient (𝑪𝒖) =

1.8. QUESTIONS:

i. What do you understand by well graded, poorly graded and uniformly graded soils?

ii. What do you understand by dry sieve and wet sieve analysis? Which once did you perform

and why?

iii. What is the grain size distribution curve? Why do you use a semi-log graph paper for

plotting it?

iv. What do you understand by GW, GP, GM, GC, SW, SP, SM, SC, SW-SM, GP-SC?


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2. HYDROMETER ANALYSIS

2.1. AIM

To determine the percentage of various size particles in a soil sample, and to classify the soil.

2.2. THEORY

Hydrometer analysis is the procedure generally adopted for determination of the particle-size

distribution in a soil for the fraction that is finer than 0.063 mm. The lower limit of the particle-size

determined by this procedure is about 0.001 mm.

In hydrometer analysis, a soil specimen is dispersed in water. In a dispersed state in water, the soil

particles will settle individually. It is assumed that the soil particles are sphered, and the velocity of the

particles can be given by Stokes’s law as

𝑣 =𝛾𝑠 − 𝛾𝑤

18𝜇∙ 𝑑2

where

𝑣 = velocity (cm/s)

𝛾𝑠 = specific weight of soil solids (g/cm3)

𝛾𝑤 = unit weight of water (g/cm3)

𝜇 = viscosity of water (g·s/cm2)

𝑑 = diameter of soil particle

If a hydrometer is suspended in water in which soil is dispersed (Fig. 5-1), it will measure the specific

gravity of the soil-water suspension at a depth 𝐻𝑟. The depth 𝐻𝑟 is called the effective depth. So, at a

time 𝑡 minutes from the beginning of the test, the soil particles that settle beyond zone of measurement

(i.e., beyond the effective depth 𝐻𝑟) will have a diameter given by

𝐻𝑟 (𝑐𝑚)

𝑡(𝑚𝑖𝑛) ∙ 60=

(𝛾𝑠 − 𝛾𝑤)(𝑔/𝑐𝑚3)

18 ∙ 𝜇 (𝑔 ∙ 𝑠𝑐𝑚2)

[𝑑 (𝑚𝑚)

10]

2

𝑑(𝑚𝑚) =10

√60√

18𝜂

𝛾𝑠 − 𝛾𝑤

√𝐻𝑟

𝑡= 𝐴√

𝐻𝑟 (𝑐𝑚)

𝑡 (min)

𝑊ℎ𝑒𝑟𝑒 𝐴 = √1800𝜇

60(𝛾𝑠 − 𝛾𝑤)= √

30𝜇

𝛾𝑠 − 𝛾𝑤


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Figure 2.1 - Hydrometer suspended in water in which the soil is dispersed

In the test procedure described here, the Cassagrande type of hydrometer will be used. From Fig 5-1 it

can be seen that, based on the hydrometer reading (which increases from 0.995 to 1.030), the value of

𝐻𝑟 will change. The magnitude of 𝐻𝑟 can be given as

𝐻𝑟 = 𝐿1 +1

2(𝐿2 −

𝑉𝐵

𝐴𝐶)

where

𝐿1 – distance between the top of hydrometer bulb to the mark for a hydrometer reading.

𝑉𝐵 – volume of the hydrometer bulb;

𝐴𝑐 – cross-sectional area of the hydrometer cylinder

Based on Eq. (5.4), the variation of 𝐻𝑟 with hydrometer reading (R) is given by the equation

𝐻𝑟 = −0.2𝑅 + 14

For actual calculation purposes we also need to know the values of A given by Equation (5.3). An

example of this calculation is shown below.

𝛾𝑠 = 𝐺𝑠 ∙ 𝛾𝑤

Where 𝐺𝑠 = 𝑠𝑝𝑒𝑐𝑖𝑓𝑖𝑐 𝑔𝑟𝑎𝑣𝑖𝑡𝑦 𝑜𝑓 𝑠𝑜𝑖𝑙 𝑠𝑜𝑙𝑖𝑑𝑠

Thus

𝐴 = √30𝜂

(𝐺𝑠 − 1) ∙ 𝛾𝑤

For example, if the temperature of the water is 25℃,

𝜂 = 0.0911 ∙ 10−4 (𝑔 ∙ 𝑠

𝑐𝑚2)

And 𝐺𝑠 = 2.7

𝐴 = √30 ∙ 0.0911 ∙ 10−4

(2.7 − 1) ∙ 1= 0.0127

The variations of A with 𝐺𝑠 and the water temperature are shown in Table 5-2.


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The CASSAGRANDE type of hydrometer is calibrated up to a reading of 30 at a temperature of 20°C

for soil particles having a 𝛾𝑠 = 2.72. From this measurement, we can determine the percentage of soil

still in suspension at time 𝑡 from the beginning of the test and all the soil particles will have diameters

smaller than 𝑑 calculated by Equation (5.2). However, in actual experimental work, some corrections

to the observed hydrometer readings need to be applied. They are as follows:

1. Temperature correction ( 𝐹𝑇 ) – The actual temperature of the test may not be 20℃ . The

tempterature correction (𝐹𝑇) may be approximated from the graph

2. Meniscus correction (𝐹𝑚) – Generally, the upper level of the meniscus is taken as the reading

during laboratory work (𝐹𝑚 is always positive).

3. Zero correction (𝐹𝑧) – A deflocculating agent is added to the soil-distilled water suspension for

performing experiments. This will change the zero reading ( 𝐹𝑧 can be either positive or

negative).

2.3. EQUIPMENT

1. Cassagrande type hydrometer

2. Mixer

3. Two 1000-cc graduated cylinders

4. Thermometer

5. Deflocculating agent

6. Spatula

7. Beaker

8. Balance

9. Plastic squeeze bottle

10. Distilled water

The equipment necessary (except the balance and the constant temperature bath) is shown in Fig. 5-2.

2.4. PROCEDURE

Note: This procedure is used when more than 90 percent of the soil is finer than No. 200 sieve.

1. Take 50 g of oven-dry, well-pulverized soil in a beaker.

2. Prepare a deflocculating agent. Usually a 4% solution of sodium hexametaphosphate (Calgon)

is used. This can be preparend by adding 40 g of Calgon in 1000 cc of distilled water and mixing

it thoroughly.

3. Take 125 cc of the mixture prepared in Step 2 and add it to the soil taken in Step 1. This should

be allowed to soak for about 8 to 12 hours.

4. Take a 1000-cc graduated cylinder and add 875 cc of distilled water plus 125 cc of deflocculating

agent in it. Mix the solution well.

5. Record the temperature of the soil suspension, T (℃).

6. Put the hydrometer in the cylinder (Step 5). Record the reading. (Note: The top of the meniscus

should be read). This is the zero correction (𝐹𝑧), which can be +𝑣𝑒 or – 𝑣𝑒. Also observe the

meniscus correction (𝐹𝑚).

7. Using a spatula, thoroughly mix the soil prepared in Step 3. Pour it into the mixer cup.

(1) Note: During this process, some soil may stick to the side of the beaker. Using the plastic squeeze

bottle filled with distilled water, wash all the remaining soil in the beaker into the mixer cup.

8. Add distilled water to the cup to make it about two-thirds full. Mix it for about two minutes

using the mixer.

9. Pour the mix into the second graduated 1000-cc cylinder. Make sure that all of the soil solids are

washed out of the mixer cup. Fill the graduated cylinder with distilled water to bring the water

level up to the 1000-cc mark.


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10. Secure a No. 12 rubber stopper on the top of the cylinder (Step 9). Mix the soil-water well by

turning the soil cylinder upside down several times.

11. Record the time immediately. This is cumulative time 𝑡 = 0. Insert the hydrometer into the

cylinder containing the soil-water suspension.

12. Take hydrometer readings at cumulative times 𝑡 = 0.5 𝑚𝑖𝑛. , 1 𝑚𝑖𝑛. , 𝑎𝑛𝑑 2 𝑚𝑖𝑛 . Always read

the upper level of the meniscus.

13. Take the hydrometer out after two minutes and put it into the cylinder next to it (Step 5).

14. Hydrometer readings are to be taken at time 𝑡 =

4 𝑚𝑖𝑛. , 8 𝑚𝑖𝑛. , 15 𝑚𝑖𝑛. , 30 𝑚𝑖𝑛. , 1 ℎ𝑟. , 2 ℎ𝑟. ,12 ℎ𝑟. , 24 ℎ𝑟. 𝑎𝑛𝑑 48 ℎ𝑟. For each reading, insert the

hydrometer into the cylinder containing the soil-water suspension about 30 seconds before the

reading is due. After the reading is taken, remove the hydrometer and put it back into the

cylinder next to it (Step 5).

2.5. CALCULATION

Refer to Table 5-4

Column 2 – These are observed hydrometer readings (R’) corresponding to times given in Column 1

Column 3 – R – corrected hydrometer reading for determination of effective length

𝑅 = 𝑅′ + 𝐹𝑚

Column 4 – Temperature

Column 5 – Temperature correction

Column 6 – corrected hydrometer reading for calculation of percent finer

𝑅𝑐 = 𝑅 + 𝐹𝑇

Column 7 – Determine (𝐻𝑟) effective length corresponding to the values of R (Col. 3)

𝐻𝑟 = −0.2𝑅 + 14

Column 8 – Determine d (mm) using Cassagrande Nomogram

Column 9 – Percent finer,

𝜌𝑠

𝜌𝑠 − 1∙

100

𝑚𝑑∙ 𝑅𝑐

2.6. GRAPH

Plot a grain-size distribution graph on semi-log graph paper with percent finer on the natural scale and

d on the log scale.


A hydrometer analysis gives results from which the percent of soil finer than 0.002 mm in diameter can

be estimated. It is generally accepted that the percent finer than 0.002 mm in size is clay or clay-size

fractions. Most clay particles are smaller than 0.001 mm, and 0.002 mm is the upper limit. The presence

of clay in a soil contributes to its plasticity.


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2.8. OBSERVATION AND CALCULATION TABLE

Table 2.1 - Sieve Analysis

Mass of soil sample taken for analysis (md) [g]

Sieve

opening,

[mm]

Mass of soil

retained on

each sieve

Percent of

mass retained

on each sieve

Cumulative

percent retained Percent finer

[g] [%] [%] [%]

in pann

Ammount

Table 2.2 - Hydrometer Analysis

Meniscus correction Fm

Dry weight of soil md g

Specific gravity of soil ρs g/cm3

Time

(min)

Hydrometer

reading R Temp.

Temperature

correction

Corrected

reading

Depth

Hr=.............................

Soil

dimension Percent finer

t R' R=R'+Fm T (°C) FT Rc=R+Ct Hr d (mm) mp (%)

30 s

1 min

2 min

4 min

8 min

15 min

30 min

1 h

2 h

12 h

24 h


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2.9. PLOT OF PERCENT FINER VS. GRAIN SIZE

Grain-size

distribution

graph

PERCENT OF Uniformity

coefficient

Coefficient of

curvature CLAY SILT SAND GRAVEL COBBLE

<0,002 0,002 – 0,063 0,063 – 2,0 2,0 - 63 63 - 200 𝐂𝐮 =𝐝𝟔𝟎

𝐝𝟏𝟎 𝐂𝐜 =

(𝐝𝟑𝟎)𝟐

𝐝𝟏𝟎 ∙ 𝐝𝟔𝟎

1

2

3


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2.10. SOIL TERNARY DIAGRAM


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3. DETERMINATION OF WATER

CONTENT

Most laboratory tests in soil mechanics require the determination of water content. Water content is

defined as

𝑤 =𝑤ℎ𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑤𝑎𝑡𝑒𝑟 𝑝𝑟𝑒𝑠𝑒𝑛𝑡 𝑖𝑛 𝑎 𝑔𝑖𝑣𝑒𝑛 𝑠𝑜𝑖𝑙 𝑚𝑎𝑠𝑠

𝑤𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑑𝑟𝑦 𝑠𝑜𝑖𝑙

Water content is usually expressed in percent.

3.1. EQUIPMENT

1. Moisture can(s).

2. Oven with temperature control.

(2) For drying, the temperature of oven is generally is kept between 105°C to 110°C. A higher

temperature should be avoided to prevent the burning of organic matter in the soil.

3. Balance. The balance should have a readability of 0.01 g for specimens having a mass of 200 g

or less. If the specimen has a mass of over 200 g, the readability should be 0.1 g.

3.2. PROCEDURE

1. Determine the mass (g) of the empty moisture can plus its cap (𝑊1), and also record the number.

2. Place a sample of representative moist soil in the can. Close the can with its cap to avoid loss of

moisture.

3. Determine the combined mass (g) of the closed can and moist soil (𝑊2)

4. Remove the cap from the top of the can and place it on the bottom (of the can).

5. Put the can (Step 4) in the oven to dry the soil to a constant weight. In most cases, 24 hours of

drying is enough.

6. Determine the combined mass (g) of the dry soil sample plus the can and its cap (𝑊3).

3.3. CALCULATION

1. Calculate the mass of moisture = 𝑊2 − 𝑊3

2. Calculate the mass of dry soil = 𝑊3 − 𝑊1

3. Calculate the water content

(3) 𝑤(%) =𝑊2−𝑊3

𝑊3−𝑊1× 100

Report the water content to the nearest 1% or 0.1% as appropriate based on the size of the specimen.


a. Most natural soils, which are sandy and gravelly in nature, may have water contents up to about

15 to 20%. In natural fine-grained (silty or clayey) soils, water contents up to about 50 to 80%

can be found. However, peat and highly organic soils with water contents up to about 500% are

not uncommon. Typical values of water content for various types of natural soils in a saturated

state are shown in Table 2-3.

b. Some organic soils may decompose during oven drying at 110°. An oven drying temperature

of 110° may be too high for soils containing gypsum, as this material slowly dehydrates.

According to ASTM, a drying temperature of 60°C is more appropriate for such soils.

c. Cooling the dry soil after oven drying (Step 5) in a desiccator is recommended. It prevents

absorption of moisture from the atmosphere.


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4. DETERMINATION OF SOIL DENSITY

4.1. AIM:

To determine the mass density of soils by core cutter method

4.2. THEORY

Density is defined as the mass per unit volume of soil

𝜌 =𝑊

𝑉

Where 𝜌 = mass density of soil

𝑊 = total mass of soil

𝑉 = total volume of soil

Figure 4.1 - Phase Diagram of Soil

Here mass and volume of soil comprise the whole soil mass. In the above figure, voids may be filled

with both water and air or only water, consequently the soil may be wet or dry or saturated. In soil the

mass of air is considered negligible and therefore the saturated density is maximum, dry density is

minimum and wet density is between the two. If soils are found below water table submerged density

is also estimated. The density can be expressed in g/cm3. For calculating the submerged density the

density of water is taken as 1 g/cm3.

Dry density of soil is calculated by using equation

𝜌𝑑 =𝜌

1 + 𝑤

𝜌𝑑 = dry density of soil

𝜌 = wet density of soil

𝑤 = water content of soil

Density of soil may be determined by core cutter test, sand replacement method and gamma ray

method. Void ration (e) is the ratio of volume of voids to volume of soil solids. Degree of saturation (𝑆)

is defined as the ratio of volume of water to volume of voids.


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𝑒 =𝑉𝑣

𝑉𝑠× 100

Where 𝑒 = voids ratio in %

𝑆 =𝑉𝑤

𝑉𝑣∙ 100

𝑆 = degree of saturation in %

𝑉𝑣 = volume of voids

𝑉𝑠 = volume of solids

𝑉𝑤 = volume of water

Further, the following relationships can be obtained

𝑒 = 𝛾𝑠 ∙𝜌𝑤

𝜌𝑑

𝑆 = 𝛾𝑠 ∙𝑤

𝑒

Where 𝛾𝑠 = specific gravity of soil solids

𝜌𝑑 = dry density

𝜌𝑤 = density of water

𝑤 = water content

A. CORE CUTTER METHOD

4.3. APPARATUS REQUIRED

1. Cylindrical core cutter

2. Steel rammer

3. Steel dolly

4.4. PROCEDURE

1. Measure the inside dimensions of the core cutter and calculate its volume;

2. Expose a small area about 30 cm2 to be tested and level it. Place the dolly on the top of the core

cutter. And drive the assembly in to the soil, with rammer until the top of the dolly protrudes

about 1.5 cm above the surface;

3. Dig the container from the surrounding soil, and allow same soil to project from the lower end

of the cutter with the help of the cutter, take out the dolly and also trim off the other end of the

cutter;

4. Find the 𝑊𝑡 of the cutter full with soil;

5. Take same specimen for water content determination;

6. Repeat the test.


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4.5. PRECAUTIONS

1. Steel dolly should be placed on the top of cutter before ramming it down.

2. Core cutter should not be used in gravels and boulders.

3. Before lifting the cutter, soil should be removed round the cutter, to minimize the disturbances.

4. While lifting the cutter, no soil should drop down.

5. During pressing and lifting the cutter care should be taken that some soil is projected at both

the ends of cutter.

6. Values should be reported to second place of decimal

4.6. OBSERVATIONS AND CALCULATION

Calculate wet density of soil

𝜌 =𝑊2 − 𝑊1

𝑉

Where

𝑊2 = mass of cutter + soil

𝑊1 = mass of cutter only

𝑉 = volume of cutter

Calculate dry density, void ratio and degree of saturation using above equations.

B. BUOYANCY METHOD

4.7. THE ARCHIMEDEAN PRINCIPLE

In accordance with the definition of density as =m/V, in order to determine the density of matter, the

mass and volume of the sample must be known.

The determination of mass can be performed directly using a weighing instrument.

The determination of volume generally cannot be performed directly. Exceptions to this rule include:

- Cases where the accuracy is nor required to be very high, and

- Measurements performed on geometric bodies, such as cubes, cuboids or cylinders, the volume

of which can easily be determined from dimensions such as length, height and diameter.

- The volume of a liquid can be measured in a graduated cylinder or in a pupette; the volume of

solids can be determined by immersing the sample in a cylinder filled with water and then

measuring the rise in the water level.

Because of the difficulty of determining volume with precision, especially when the sample has highly

irregular shape, a “detour” is often taken when determining the density, by making use of the

Archimedean Principle, which describes the relation between forces (or masses), volumes and densities

of solid samples immersed in liquid:

From everyday experience, everyone is familiar with the effect that an object or body appears to be

lighter than in air – just like your own body in a swimming pool.


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Figure 4.2 - The force exerted by a body on a spring scale in air (left) and in water (right)

Both the cause of this phenomenon and the correlation between the values determined in its

measurement are explained in detail in the following.

Observing the ratio of forces exerted on the immersed body and the water displaced by the body, it can

be seen that the forces exerted include both the weight 𝑊𝑠, a downward force, and buoyancy 𝐹𝐵, an

upward force. The resulting force can be calculated from the difference between these two forces: 𝐹𝑟𝑒𝑠 =

𝑊𝑠 ∙ 𝐹𝐵. The buoyancy 𝐹𝐵 exerted on the body is equal to the weight of the liquid displaced by the body.

4.8. PROCEDURE

The buoyancy method is often used to determine the density of bodies and liquids. The apparent

weight of a body in a liquid, i.e., the weight as reduced by the buoyancy force is measured. This value

is used in combination with the weight in air to calculate the density.

Figure 4.3 - Basic procedure for the buoyancy method with below-balance weighing

In the procedure illustrated in Figure , the values displayed on the weight readout indicate the mass of

the immersed body as reduced by buoyancy.

This means that, in light of the equation 𝜌𝑠 = 𝜌𝑓𝑙(𝑚𝑠/𝑚𝑓𝑙), the mass of the body weighed in air is

known: 𝑚𝑠 = 𝑚(𝑎). The mass of the liquid 𝑚𝑓𝑙 is not directly known, but is yielded by the difference

between the weights of the body in air (𝑚(𝑎)) and in liquid (𝑚(𝑓𝑙)):

𝑚𝑓𝑙 = 𝑚(𝑎) − 𝑚(𝑓𝑙)

The density of the body can be determined with the following equation:

𝜌𝑠 = 𝜌𝑓𝑙 ∙𝑚(𝑎)

𝑚(𝑎) − 𝑚(𝑓𝑙)


19

WATER CONTENT

Elemente de calcul UM Sample no.

1 2 3

Weight of container 𝑊1 g

Weight of container + wet soil 𝑊2 g

Weight of container + dry soil 𝑊3 g

Water content 𝑤 =𝑊2 − 𝑊3

𝑊3 − 𝑊1∙ 100 %

AVERAGE VALUE medw

%

CORE CUTTER TEST

Computation elements UM Sample no.

1 2 3 4

Mass of cutter only 𝑊2 g

Mass of cutter + soil 𝑊1 g

Volume of cutter 𝑉 cm3

Soil density 𝜌 =𝑚1 − 𝑚2

𝑉 g/cm3

AVERAGE VALUE medρ g/cm3

BUOYANCY METHOD

Computation elements UM Sample no.

1 2 3 4

Weight of the soil 𝑊0 g

Weight of the soil sample + weight of

the paraffin coating in air 𝑊1 g

Weight of the soil sample + weight of

the paraffin coating in water 𝑊2 g

Volume of the paraffined soil sample 𝑉1 =𝑚1 − 𝑚2

𝜌𝑤 cm3

Volume of the paraffin coating 𝑉2 =𝑚1 − 𝑚0

𝜌𝑝 cm3

Soil density 𝜌 =𝑚0

𝑉1 − 𝑉2 g/cm3

AVERAGE VALUE 𝜌𝑎𝑣𝑟 g/cm3


20

No. Soil index Computation equation U.M. Value

1 Bulk density - g/cm3

2 Wet density - g/cm3

3 Water content - %

4 Void ratio e = -

5 Porosity n = %

6 Wet specific gravity γ = kN/m3

7 Dry specific gravity γd = kN/m3

8 Saturated specific gravity γsat = kN/m3

9 Submerged specific

gravity γ’ = kN/m3

10 Degree of saturation Sr = %


21

5. LIQUID LIMIT TEST

5.1. INTRODUCTION

When a cohesive soil is mixed with an excessive amount of water, it will be in a somewhat liquid state

and flow like a viscous liquid. However, when this viscous liquid is gradually dried, with the loss of

moisture it will pass into a plastic state. With further reduction of moisture, the soil will pass into a

semisolid and then into a solid state. This is shown in Fig. 6-1. The moisture content (in percent) at

which the cohesive soil will pass from a liquid state to a plastic state are reffered to as the plastic limit

of the soil. Similarly, the moisture contents (in percent) at which the soil changes from a plastic to a

semisolid state and from a semisolid state to a solid state are referred to as the plastic limit and the

shrinkage limit, respectively. These limits are referred to as the Atterberg limits (1911). In this chapter,

the procedure to determine the liquid limit of a cohesive soil will be discussed.

Figure 5.1 – Atterberg limits

5.2. AIM

1. Prepare soil specimen as per specification

2. Find the relationship between water content and number of blows

3. Draw flow curve

4. Find out liquid limit

5.3. NEED AND SCOPE

Liquid limit is significant to know the stress history and general properties of soil met with

construction. From the results of liquid limit test the compression index may be estimated. The

compression index value will help us in settlement analysis. If the natural moisture content of soil is

closer to liquid limit, the soil can be considered as soft if the moisture content is lesser than liquids limit,

the soil can be considered as hard. The soil is brittle and stiffer.

5.4. THEORY

The liquid limit is the moisture content at which the groove, formed by a standard tool into the sample

of soil taken in the standard cup, closes for 10 mm on being given 25 blows in a standard manner. At

this limit the soil possess low shear strength.

5.5. APPARATUS REQUIRED

1. Casagrande liquid limit device

2. Grooving tool

3. Balance sensitive up to 0.01 g

4. Mixing dishes

5. Spatula

6. Electrical Oven


22

The Casagrande liquid limit device essentially consists of a brass cup that can be raised and dropped

through a distance of 10 mm on a hard rubber base by a cam operated by a crank (see Fig. 6-3a). Fig 6-

3b shows a schematic diagram of a grooving tool

5.6. PROCEDURE

1. Determine the mass of three moisture cans (𝑀0)

2. Put about 250 g of air-dry soil, passed through No. 40 sieve, into an evaporating dish. Add water

from the plastic squeeze bottle and mix the soil to the form of a uniform paste.

3. Place a portion of the paste in the brass cup of the liquid limit device. Using the spatula, smooth

the surface of the soil in the cup such that the maximum depth of the soil is about 8 mm.

4. Using the grooving tool, cut a groove along the center line of the soil pat in the cup (Fig. 6-4a)

Figure 5.2 – Schematic diagram of (a) casagrande liquid limit device; (b) grooving tool

5. Turn the crank of the liquid limit device at the rate of about 2 revolutions per second. By this,

the liquid limit cup will rise and drop through a vertical distance of 10 mm once for each

revolution. The soil from two sides of the cup will begin to flow toward the center. Count the

number of blows, N, for the groove in the soil to close through a distance of ½ inch (12.7 mm)

as shown in Fig. 6-4b.

Figure 5.3 – schematic diagram of soil pat in the cup of the liquid limit device at (a) beginning of test,

(B) end of test


23

(4) If N = about 25 to 35, collect a moisture sample from the soil in the cup in a moisture can. Close

the cover of the can, and determine the mass of the can plus the moisture soil (𝑀1).

(5) Remove the rest of the soil paste from the cup to the evaporating dish. Use paper towels to

thoroughly clean the cup.

(6) If the soil is too dry, N will be more than about 35. In that case, remove the soil with the spatula

to the evaporating dish. Clean the liquid limit cup thoroughly with paper towels. Mix the soil in

the evaporating dish with more water, and try again.

(7) If the soil is too wet, N will be less than about 25. In that case, remove the soil in the cup to the

evaporating dish. Clean the liquid limit cup carefully with paper towels. Stir the soil paste with

the spatula for some time to dry it up. The evaporating dish may be placed in the oven for a few

minutes for drying also. Do not add dry soil to the wet soil paste to reduce the moisture content

for bringing it to the proper consistency. Now try again in the liquid limit device to get the groove

closure of ½ in. (12.7 mm) between 25 and 35 blows.

6. Add more water to soil paste in the evaporating dish and mix thoroughly. Repeat Steps 3, 4 and

5 to get a groove closure of ½ in (12.7 mm) in the liquid limit device at a blow count N=20 to

25. Take a moisture sample from the cup. Remove the rest of the soil paste to the evaporating

dish. Clean the cup with paper towels.

7. Add more water to the soil paste in the evaporating dish and mix well. Repeat Steps 3, 4 and 5

to get a blow count N between 15 and 20 for a groove closure of ½ in (12.7 mm) in the liquid

limit device. Take a moisture sample from the cup.

8. Put the three moisture cans in the oven to dry to constant masses (𝑀2). (The caps of the moisture

cans should be removed from the top and placed at the bottom of the respective cans in the

oven).

5.7. COMPUTATION/CALCULATION

Draw a graph showing the relationship between water content (on y-axis) and number of blows (on x-

axis) on semi-log graph. The curve obtained is called flow curve. The moisture content corresponding

to 25 drops (blows) as read from the represents liquid limit. It is usually expressed to the nearest whole

number.


24

6. PLASTIC LIMIT TEST

6.1. INTRODUCTION

Plastic limit is defined as the moisture content, in percent, at which a cohesive soil will change from a

plastic state to a semisolid state. In the laboratory, the plastic limit is defined as the moisture content

(%) at which a thread of soil will just crumble when rolled to a diameter of 3-4 mm. This test might be

seen as somewhat arbitrary and, to some extent, the result may depend on the person performing the

test. With practice, however, fairly consistent results may be obtained.

6.2. EQUIPMENT

1. Porcelain evaporating dish

2. Spatula

3. Plastic squeeze bottle with water

4. Moisture can

5. Ground glass plate


6.3. PROCEDURE

1. Put approximately 20 grams of a representative, air-dry soil sample, passed through a sieve,

into a porcelain evaporating dish.

2. Add water from the plastic squeeze bottle to the soil and mix thoroughly

3. Determine the mass of a moisture can in grams and record it on the data sheet (𝑊1).

4. From the moist soil prepared in Step 2, prepare several ellipsoidal-shaped soil masses by

squeezing the soil with your fingers

5. Take one of the ellipsoidal-shaped soil masses (Step 4) and roll it on a ground glass plate using

the palm of your hand. The rolling should be done at the rate of about 80 strokes per minute.

Note that one complete backward and one complete forward motion of the palm constitute a

stroke.

6. When the thread is being rolled in step 5 reaches 3-4 mm in diameter, break it up into several

small pieces and squeeze it with your fingers to form an ellipsoidal mass again.

7. Repeat Steps 5 and 6 until the thread crumbles into several pieces when it reaches a diameter of

3-4 mm. It is possible that a thread may crumble at a diameter larger than 3-4 mm during a

given rolling process, whereas it did not crumble at the same diameter during the immediately

previous rolling

8. Collect the small crumbled pieces in the moisture can put the cover on the can.

9. Take the other ellipsoidal soil masses formed in Step 4 and repeat Steps 5 through 8.

10. Determine the mass of the moisture can plus the wet soil (𝑊2) in grams. Remove the cap from

the top of the can and place it into the oven (with the cap at the bottom of the cam).

11. After about 24 hours, remove the can from the oven and determine the mass of the can plus the

dray soil (𝑊3) in grams.

6.4. CALCULATIONS

𝑤𝑃 (𝑃𝐿) =𝑚𝑎𝑠𝑠 𝑜𝑓 𝑚𝑜𝑖𝑠𝑡𝑢𝑟𝑒

𝑚𝑎𝑠𝑠 𝑜𝑓 𝑑𝑟𝑦 𝑠𝑜𝑖𝑙=

𝑊2 − 𝑊3

𝑊3 − 𝑊1∙ 100


25

Computation elements UM Plastic limit (wP) Liquidity limit (wL)

1 2 3 1 2 3 4

Can no -

Mass of can, 𝑊1 g

Mass of can + moist soil, 𝑊3 g

Mass of can + dry soil, 𝑊3 g

Water content, 𝑤 %

Number of blows, 𝑁

PLASTIC LIMIT Pw

LIQUIDITY LIMIT Lw

WATER CONTENT w

PLASTICITY INDEX PI

CONSISTENCY INDEX CI


26

7. DETERMINATION OF RELATIVE

DENSITY OR DENSITY INDEX OF SAND

7.1. AIM

To determine the relative density or density index of cohesionless soil

7.2. THEORY

Relative density is also known as density index. It is defined as the ratio of difference between the void

ratio of a cohesionless soil (i.e. sand) in the loosest state and any given void ratio to the difference

between its void ratios in the loosest state and in the densest state.

7.3. APPARATUS

1. Vibratory table

2. Molds

3. Surcharge weights

4. Dial gauge

5. Pouring device

6. Mixing pans

7. Weighing scale

8. Steel straight edge

9. Metal hand scoop

7.4. PROCEDURE

The test procedure to determine the relative density of soil involves the measurement of density of soils

in its loosest possible state (𝜌𝑚𝑖𝑛 ) and densest possible state (𝜌𝑚𝑎𝑥). Knowing the specific gravity of soil

solids (𝛾𝑠) the void ratios of the soil in its loosest state (𝑒𝑚𝑎𝑥) and densest state (𝑒𝑚𝑖𝑛) are computed.

The density of soil in the field (𝜌) is used to compute the void ratio (𝑒) in the field. After obtaining the

three void ratios (i.e. minimum, maximum and natural) the relative density is computed. The two

moulds (3000 cm3 or 15000 cm3) are used depending upon the maximum size of soil particle present.

A representative sample of soil should be selected. The weight of soil sample to be taken depends upon

the maximum size of particles in the soil as given in the table below. The soil sample should be dried

in an oven at a temperature of 105°C to 110°C. The soil sample should be pulverized without breaking

the individual soil particles and sieved through the required sieve.

The first step is to calibrate these molds. Then the possible minimum and maximum densities of the

soil are obtained as explained below.

7.5. PROCEDURE FOR THE DETERMINATION OF MINIMUM DENSITY

1. The pouring device and mold should be selected according to the maximum size of particle as

indicated in the table above. The mold should be weighed and weight recorded. Oven dry soil

should be used.

2. Soil containing particles smaller than 10 mm should be placed as loosely as possible in the mold

by pouring the soil through the spout in a steady stream. The spout should be adjusted so that

the height of free fall of the soil is always 25 mm. while pouring the soil, the pouring device

should be moved in a spiral motion from the outside towards the center to form a soil layer of


27

uniform thickness without segregation. The mold should be filled approximately 25 mm above

the top and leveled with the top by making one continuous pass with the steel straight edge. If

all excess material is not removed, an additional continuous pass should be made. Great care

shall be exercised to avoid jarring during the entire pouring and trimming operation.

3. The mold and the soil should be weighed and the weight recorded.

4. Soil containing particles larger than 10 mm should be placed by means of a large scoop (or

shovel) held as close as possible to and just above the soil surface to cause the material to slide

rather than fall into previously placed soil. If necessary, larger particles may be held by hand to

prevent them from rolling off the scoop. The mold should be filled to overflowing but not more

than 25 mm above the top. The surface of the soil should be leveled with the top of the mold

using the steel straight edge in such a way that any slight projections of the larger particles

above the top of the mold shall approximately balance the large voids in the surface below the

top of the mold. The mold and the soil should be weighed and the weighed and the weight

recorded.

7.6. PROCEDURE FOR THE DETERMINATION OF MAXIMUM DENSITY

The maximum density of soil may be determined by either dry or wet method.

1. The guide sleeve should be assembled on top of the mold and the clamp assemblies tightened

so that the inner surfaces of the walls of the mold and the sleeve are in line. The lock nuts should

be tightened. The third clamp should be loosened, the guide sleeve removed, the empty mold

weighed and its weight recorded.

2. The mold should then be filled with the thoroughly mixed oven dry soil in a loose state.

3. The guide sleeves should be attached to the mold and the surcharge base plate should be placed

on the soil surface. The surcharge weight should then be lowered on to the base plate using the

hoist in the case of the 15000 cm3 mold.

4. The mold should be fixed to the vibrator deck. The assembly of mold fixed on to the vibrating

table is shown in the figure below. The vibrator control should be set at its maximum amplitude

and the loaded soil specimen should be vibrated for 8 minutes.

5. The surcharge weight and the guide sleeves should be removed from the mold. The dial gauge

readings on two opposite sides of the surcharge base plate should be obtained and the average

recorded. The mold with the soil should be weighed and its weight recorded.


28

Computation elements UM Minimum density Maximum density

1 2 3 1 2 3

Weight of mould g

Weight of soil + mould g

Volume of mould cm3

Density g/cm3

MINIMUM DENSITY minρ

MAXIMUM VOID RATIO maxe

MAXIMUM DENSITY maxρ

MINIMUM VOID RATIO mine

NATURAL DENSITY ρ

NATURAL VOID RATIO e

RELATIV DENSITY DI


29

8. SOIL PERMEABILITY

8.1. INTRODUCTION

Soils are permeable due to the existence of interconnected voids through which water can flow from

points of high energy to points of low energy. The study of the flow of water through permeable soil

media is important in soil mechanics. It is necessary for estimating the quantity of underground

seepage under various hydraulic conditions, for investigating problems involving the pumping of

water for underground construction, and for making stability analyses of earth dams and earth-

retaining structures that are subjected to seepage forces.

The rate of flow of water through a soil specimen of gross-sectional area, 𝐴, can be expressed as

𝑞 = 𝑘 ∙ 𝑖 ∙ 𝐴

where 𝑞 = flow in unit time

𝑘 = coefficient of permeability

𝑖 = hydraulic gradient

For coarse sands, the value of the coefficient of permeability may vary from 1 to 0.01 cm/s and, for fine

sand, it may be in the range of 0.01 to 0.001 cm/s.

The coefficient of permeability of sands can be easily determined in the laboratory by two simple

methods. They are (a) the constant head test and (b) the variable head test.

8.2. EQUIPMENT

1. Falling head permeameter

2. Balance sensitive to 0.1 g

3. Thermometer

4. Stop watch

A schematic diagram of a falling head permeameter is shown in Fig. 11-1. The top of the specimen tube

is connected to a burette by plastic tubing. The specimen tube and the burette are held vertically by

clamps from a stand. The bottom of the specimen tube is connected to a plastic funnel by a plastic tube.

The funnel is held vertically by a clamp from another stand. A scale is also fixed vertically to this stand.

8.3. PROCEDURE

1. Determine the mass of the plastic specimen tube, the porous stones, the spring, and the two

rubber stoppers (𝑊1).

2. Slip the bottom porous stone into the specimen tube, and then fix the bottom rubber stopper to

the specimen tube.

3. Collect oven-dry sand in a container. Use a spoon, pour the sand into the specimen tube in small

layers, and compact it by vibration and/or other compacting means.

(8) Note: By changing the degree of compaction, a number of test specimens having different void

ratios can be prepared.

4. When the length of the specimen tube is about two-third the length of the tube, slip the top

porous stone into the tube to rest firmly on the specimen.

5. Place a spring on the top porous stone, if necessary.

6. Fix a rubber stopper to the top of the specimen tube.

(9) Note: The spring in the assembled position will not allow any expansion of the specimen volume,

and thus the void ratio, during the test.

7. Determine the mass of the assembly (Step 6 - 𝑊2).

8. Measure the length (𝐿) of the compacted specimen in the tube


30

9. Assemble the permeameter near a sink, as shown in Fig 10.

Figure 8.1 - permeameter

10. Supply water using a plastic tube from the water inlet to the burette. The water will flow from

the burette to the specimen and then to the funnel. Check to see that there is no leak. Remove

all air bubbles.

11. Allow the water to flow for some time in order to saturate the specimen. The pinchcock is

located on the plastic pipe connecting the bottom of the specimen to the funnel.

12. Using the pinchcock, close the flow of water through the specimen to the funnel.

13. Measure the head difference, ℎ1 (cm)

(10) Note: Do not add any more water to the burette.

14. Open the pinchcock. Water will flow through the burette to the specimen and then out of the

funnel. Record time (𝑡) with a stopwatch until the head difference is equal to ℎ2 (cm). Close the

flow of water through the specimen using the pinchcock.

15. Determine the volume (𝑉𝑤) of water that is drained from the burette in cm3.

16. Add more water to the burette to make another run. Repeat Steps 13, 14 and 15. However, ℎ1

and ℎ2 should be changed for each run.

17. Record the temperature, 𝑇, of the water to the nearest degree (℃).

8.4. CALCULATION

The coefficient of permeability can be expressed by the relation

𝑘 = 2.303 ∙𝑎 ∙ 𝐿

𝐴 ∙ 𝑡∙ 𝑙𝑜𝑔 (

ℎ1

ℎ2)

Where 𝑎 = inside cross sectional area of the burette


31

SPECIMEN CHARACTERISTICS

Test No. Symbol UM Test no.

1 2 3

Diameter of specimen D cm

Length of specimen L cm

Area of specimen A cm2

Inside cross-sectional area of the burette a cm2

Water temperature T °C

Correction coefficient c -

RECORDED VALUES

Specimen

No.

Test

duration

Begginning

head

difference

Ending

head

difference 𝑙𝑛 (

ℎ1

ℎ2)

Permeability coefficient at 20°C

𝑡 ℎ1 ℎ2 𝑘𝑡 = 𝑐 ∙𝑎 ∙ 𝐿

𝑡 ∙ 𝐴∙ 𝑙𝑛 (

ℎ1

ℎ2) Average

s cm cm - cm/s cm/s

1

2

3


32

9. STANDARD PROCTOR COMPACTION

TEST

9.1. INTRODUCTION

For construction of highways, airports, and other structures, it is often necessary to compact soil to

improve its strength. Proctor (1933) developed a laboratory compaction test procedure to determine

the maximum dry unit weight of compaction of soils which can be used for specification of field

compaction. This test is referred to as the standard Proctor compaction test and is based on the

compaction of soil fraction passing 4 mm sieve.

In the construction of highway embankments, earth dams, and many other engineering structures,

loose soils must be compacted to increase their unit weights. Compaction increases the strength

characteristics of soils, which increase the bearing capacity of foundations constructed over them.

Compaction also decreases the amount of undesirable settlement of structures and increases the

stability of slopes of embankments. Smooth-wheel rollers, sheep foot rollers, rubber-tired rollers, and

vibratory rollers are generally used in the field for soil compaction. Vibratory rollers are used mostly

for the densification of granular soils. Vibroflot devices are also used for compacting granular soil

deposits to a considerable depth. Compaction of soil in this manner is known a vibroflotation.

9.2. EQUIPMENT

1. Compaction mold

2. Standard Proctor hammer (2.5 kg)



5. Large flat pan

6. Jack

7. Steel straight edge

8. Moisture cans

9. Drying oven

10. Plastic squeeze bottle with water

Figure 9.1 shows the equipment required for the compaction test with the exception of the jack, the

balances, and the oven.

9.3. PROCTOR COMPACTION MOLD AND HAMMER

A schematic diagram of the Proctor compaction mold, which is 102 mm in diameter and 112 mm in

height, is shown in Figure 9.1a. There is a base plate and an extension that can be attached to the top

and bottom of the mold, respectively.

Figure 9.1b shows the schematic diagram of a standard Proctor hammer. The hammer can be lifted and

dropped through a vertical distance of 30.5 cm

9.4. PROCEDURE

1. Obtain about 4.5 kg of air-dry soil on which the compaction test is to be conducted. Break all

soil lumps.

2. Sieve the soil on a 4 mm sieve. Collect all the minus – 4 material in a large pan. This should be

about 2.7 kg or more.

3. Add enough water to the ≤ 4 mm material and mix it in thoroughly to bring the moisture content

up to about 5%.


33

4. Determine the weight of the Proctor mold (not extension), 𝑊1.

5. Now attach the extension to the top of the mold.

6. Pour the moist soil into the mold in three equal layers. Each layer should be compacted

uniformly by the standard Proctor hammer 25 times before the next layer of loose soil is poured

into the mold.

Note: The layers of loose soil that are being poured into the mold should be such that, at the end of

the three-layer compaction, the soil should extend slightly above the top of the rim of the

compaction mold.

(11)

Figure 9.1 – Standard proctor mold and hammer

7. Remove the top attachment from the mold. Be careful not to break off any of the compacted soil

inside the mold while removing the top attachment

8. Using a straight edge, trim the excess soil above the mold. Now the top of the compacted soil

will be even with the top of the mold.

9. Remove the base plate from the mold.

10. Determine the weight of the mold + compacted moist soil in the mold, 𝑊2. Using a jack, extrude

the compacted soil cylinder from the mold.

11. Take a moisture can and determine it’s mass, 𝑊3 (g).

12. From the moist soil extruded in Step 10, collect a moisture sample in the moisture can (Step 11)

and determine the mass of the can + moist soil 𝑊4 (g).

13. Place the moist can with the moist soil in the oven to dry to a constant weight.

14. Break the rest of the compacted soil (to ≤ 4 mm size) by hand and mix it with the left over moist

soil in the pan. Add more water and mix it to raise the moisture content by about 2%.

15. Repeat Steps 6 through 12. In this process, the weight of the mold + moist soil (𝑊2) will first

increase with the increase in moisture content and then decrease. Continue the test until at least

two successive down readings are obtained.

16. The next day, determine the mass of the moisture cans + soil samples, 𝑊5 (g) (from step 13)



34

In most of the specifications for earth work, it is required to achieve a compacted field dry unit weight

of 90% to 95% of the maximum dry unit weight obtained in the laboratory. This is sometimes referred

to as relative compaction, 𝐷, or

𝐷(%) =𝜌𝑑(𝑓𝑖𝑒𝑙𝑑)

𝜌𝑑 𝑚𝑎𝑥 (𝑙𝑎𝑏)∙ 100

For granular soils, it can be shown that

𝐷(%) =𝐷0

1 − 𝐷𝑟(1 − 𝑅0)∙ 100

where 𝐷𝑟 relative density of compaction

𝐷0 =𝜌𝑑 𝑚𝑎𝑥

𝜌𝑑 𝑚𝑖𝑛

Compaction of cohesive soils will influence its structure, coefficient of permeability, one-dimensional

compressibility and strength. For further discussion on this topic, refer to Das (1994).

Bulk density of soil: sρ = g/cm3

Compaction

Test

parameters

Mold Hammer Number of

layers

Number of

blows/layer (n) d

[mm]

h

[mm]

V

[cm3]

D

[mm]

H

[mm]

m

[kg]

Test No. 1 2 3 4 5 6 7 8

Weight of the mold + moist

soil, 𝑊2 g

Weight of the mold, 𝑊1 g

Weight of moist soil, 𝑊2 − 𝑊1 g

Moist density,

𝜌 =𝑊1 − 𝑊2

𝑉

g/cm3

Water content can number -

Mass of can, 𝑊3 g

Mass of can + moist soil, 𝑊4 g

Mass of can + dry soil, 𝑊5 g

Water content, 𝑤 %

Dry density

𝜌𝑑 =𝜌

1 +𝑤

100

g/cm3


35

10. CONSOLIDATION TEST

10.1. INTRODUCTION

This method covers the determination of the magnitude and rate of the consolidation of a saturated or

near-saturated specimen of soil (see note 1) in the form of a disc confined laterally, subjected to vertical

axial pressure, and allowed to drain freely from the top and bottom surfaces. The method is concerned

mainly with the primary consolidation phase, but it can also be used to determine secondary

compression characteristics. In this test the soil specimen is loaded axially in increments of applied

stress. Each stress increment is held constant until the primary consolidation has ceased. During this

process water drains out of the specimen, resulting in a decrease in height which is measured at suitable

intervals. These measurements are used for determination of the relationship between compression (or

strain) or voids ratio and effective stress, and for the calculation of parameters which describe the

amount of compression and the rate at which it takes place

Consolidation is the process of time-dependent settlement of saturated clayey soil when subjected to

an increased loading. In this chapter, the procedure of a one-dimensional laboratory consolidation test

will be described, and the methods of calculation to obtain the void ratio-pressure curve (e vs log p),

the preconsolidation pressure (𝑝𝑐) and the coefficient of consolidation (𝑐𝑣) will be outlined.

10.2. EQUIPMENT

(1) Consolidation apparatus

(2) Specimen trimming device

(3) Wire saw

(4) Balance sensitive to 0.01 g

(5) Stopwatch

(6) Moisture can

(7) Oven

10.3. CONSOLIDATION TEST UNIT

The consolidation test unit consists of a consolidometer and a loading device. The consolidometer can

be either (i) a floating ring consolidometer (Figure 10.1a) or (ii) a fixed ring consolidometer (Figure

10.1b). The floating ring consolidometer usually consists of a brass ring in which the soil specimen is

placed. One porous stone is placed at the top of the specimen and another porous stone at the bottom.

The soil specimen in the ring with the two porous stones is placed on a base plate. A plastic ring

surrounding the specimen fits into a groove on the base plate. Load is applied through a loading head

that is placed on the top porous stone. In the floating ring consolidometer, compression of the soil

specimen occurs from the top and bottom towards the center.

Figure 10.1 – Schematic diagram of (a) floating ring consolidometer; (b) fixed ring consolidometer


36

The fixed ring consolidometer essentially consists of the same components, i.e. a hollow base plate, two

porous stones, a brass ring to hold the soil specimen, and a metal ring that can be fixed tightly to the

top of the base plate. The ring surrounds the soil specimen. A stand pipe is attached to the side of the

base plate. This can be used for permeability determination of soil. In the fixed ring consolidometer,

the compression of the specimen occurs from the top towards the bottom.

The specifications for the loading devices of the consolidation test unit vary depending upon the

manufacturer. During the consolidation test, when load is applied to the soil specimen, the nature of

variation of side friction between the surrounding brass ring and the specimen are different for the

fixed ring and the floating ring consolidometer, and this is shown in Figure 10.2. In most cases, a side

friction of 10% of the applied load is a reasonable estimate.

Figure 10.2 – Nature of variation of soil-ring friction per unit contact areas in (a) fixed ring

consolidometer; (b) floating ring consolidometer

10.4. PROCEDURE

(1) Prepare a soil specimen for the test. The specimen is prepared by trimming an undisturbed

natural sample obtained in Shelby tubes. The shelby tube sample should be about (6.35 to 12.7

mm) larger in diameter than the specimen diameter to be prepared for the test.

(2) Collect some excess soil that has been trimmed in a moisture can for moisture content

determination.

(3) Collect some of the excess soil trimmed in Step (1) for determination of the particle density, 𝛾𝑠.

(4) Determine the mass of the consolidation ring (𝑚1) in grams.

(5) Place the soil specimen in the consolidation ring. Use the wire saw to trim the specimen flush

with the top and bottom of the consolidation ring. Record the size of the specimen, i.e. height

[𝐻𝑡(𝑖)] and the diameter (𝐷).

(6) Determine the mass of the consolidation ring and the specimen (𝑚2) in grams.

(7) Saturate the lower porous stone on the base of the consolidometer

(8) Place the soil specimen in the ring over the lower porous stone

(9) Place the upper porous stone on the specimen in the ring

(10) Attach the top ring to the base of the consolidometer

(11) Add water to the consolidometer to submerge the soil and keep it saturated. In the case of the

fixed ring consolidometer, the outside ring (which is attached to the top of the base) and the

stand pipe connection attached to the base should be kept full with water. This needs to be done

for the entire period of the test.

(12) Place the consolidometer in the loading device

(13) Attach the vertical deflection dial gauge to measure the compression of soil. It should be fixed

in such as way that the dial is at the beginning of its release run. The dial gauge should be

calibrated to read as 1 small division = 0.01 mm


37

(14) Apply the load to the specimen such that the magnitude of the pressure, 𝑝, on the specimen is

(50 kPa). Take the vertical deflection dial gauge readings at the following times, 𝑡, counted from

the time of load application – 0 min, 0.25 min, 0.50 min, 1 min, 2 min, 4 min, 8 min, 15 min, 30

min, 60 min, 120 min, 240 min, 480 min and 1440 min.

(15) The next day, add more load to the specimen such that the total magnitude of pressure on the

specimen becomes 100 kPa. Take the vertical dial gauge reading at similar time intervals as stated

in Step (14).

(16) Repeat Step (15) for soil pressure magnitudes of 200 kPa, 400 kPa and 800 kPa.

(17) At the end of the test, remove the soil specimen and determine its moisture content

Figure 10.3 – Plot of dial reading vs. √𝑡𝑖𝑚𝑒 for the test results given in Table . Determination to 𝑡90 by

square-root-of-time method

10.5. CALCULATION AND GRAPH

(1) Collect all of the time vs vertical dial readings data.

(2) Determine the time for 90% primary consolidation, 𝑡90, from each set of time vs. vertical dial

readings. An example of this is shown in Figure 10.3, which is a plot of the results of vertical dial

reading vs. √𝑡𝑖𝑚𝑒. Draw a tangent AB to the initial consolidation curve. Measure the length BC.

The abscissa of the point of intersection of the line AD with the consolidation curve will give

√𝑡90. This technique is referred to as the square-root-of-time fitting method (Taylor, 1942).

(3) Determine the time for 50% primary consolidation, 𝑡50, from each set of time vs. vertical dial

readings. The procedure for this is shown in Figure 10.4, which is a semilog plot (vertical dial

reading in natural scale and time in log scale) for set of readings. Project the straight line portion

of the primary consolidation downward and the straight line portion of the secondary

consolidation backward. The point of intersection of these two lines is A. The vertical dial

reading corresponding to A is 𝑑100 (dial reading at 100% primary consolidation). Select times 𝑡1

and 𝑡2 = 4𝑡1. (Note: 𝑡1 and 𝑡2 should be within the top curved portion of the consolidation plot.)

Determine the difference in dial readings, 𝑋, between times 𝑡1 and 𝑡2. Plot line BC, which is

vertically X distance above the point on the consolidation curve corresponding to time 𝑡1. The

vertical dial gauge corresponding to line BC is 𝑑0 , i.e. the reading for 0% consolidation.

Determine the dial gauge reading corresponding to 50% primary consolidation as

(4) 𝑑50 =𝑑0+𝑑100

2


38

(5) The time corresponding to 𝑑50 on the consolidation curve is 𝑡50. This is the logarithm-of-time

curve fitting method (Casagrande and Fadum, 1940).

(6) Complete the experimental data

(7) Determine the height of solids (𝐻𝑠) of the specimen in the mold as

(8) 𝐻𝑠 =𝑊𝑠

(𝜋∙𝐷2

4)∙𝜌𝑠∙𝜌𝑤

where 𝑊𝑠 = dry mass of soil specimen

𝐷 = diameter of the specimen

𝜌𝑠 = density of soil solids

𝜌𝑤 = density of water

(9) Determine the change in height, ∆𝐻, of the specimen due to load increments from 𝑝 to 𝑝 + ∆𝑝.

(10) Determine the final specimen height, 𝐻𝑡(𝑓), at the end of consolidation due to a given load.

(11) Determine the height of voids, 𝐻𝑣, in the specimen at the end of consolidation due to a given

loading, 𝑝, as

𝐻𝑣 = 𝐻𝑡(𝑓) − 𝐻𝑠

(12) Determine the final void ratio at the end of consolidation for each loading, 𝑝, as

𝑒 =𝐻𝑣

𝐻𝑠

Figure 10.4 – Logarithm of time curve fitting method for laboratory results

(13) Determine the average specimen height, 𝐻𝑡(𝑎𝑣) , during consolidation for each incremental

loading.

(14) Calculate the coefficient of consolidation, 𝑐𝑣, from 𝑡90

𝑐𝑣 =𝑇𝑣 ∙ 𝐻𝑡(𝑎𝑣)

2

4 ∙ 𝑡90

𝑇𝑣 – time factor 𝑡90 = 0.848

(15) Calculate the coefficient of consolidation, 𝑐𝑣 from 𝑡50

𝑇𝑣(50%) = 0.197 =𝑐𝑣 ∙ 𝑡50

𝐻2=

𝑐𝑣 ∙ 𝑡50

[𝐻𝑡(𝑎𝑣)

2 ]2

𝑐𝑣 =0.197𝐻𝑡(𝑎𝑣)

2

4 ∙ 𝑡50


39

(16) Plot a semilogarithmic graph of pressure vs. final void ratio. Pressure, 𝑝, is plotted on the log

scale and the final void ratio on the linear scale. Note: The plot has a curved upper portion and,

after that, e vs. log p has a linear relationship.

(17) Calculate the compression index, 𝐶𝑐. This is the slope of the linear portion of the e vs. log p plot

(Step (13))

𝐶𝑐 =𝑒1 − 𝑒2

log𝑝2𝑝1

(18) On the semilogarithmic graph, using the same horizontal scale (the scale for p), plot the values

of 𝑐𝑣.

(19) Determine the preconsolidation pressure, 𝑝𝑐. The procedure can be explained with the aid of

the e-log p graph (Casagrande, 1936). First, determine point A, which is the point on the e-log p

plot that has the smallest radius of curvature. Draw a horizontal line AB. Draw a line AD which

is the bisector of angle BAC. Project the straight line portion of the e-log p plot backwards to

meet line AD at E. The pressure corresponding to point E is the preconsolidation pressure.

Figure 10.5 – Plot of void ratio and the coefficient of consolidation against pressure


40

Consolidation test – specimen details

Location Job ref.

Borehole/Pit no.

Soil description Sample no.

Depth

Date

Test method:

Cell no.

Ring no.

Particle density

measured/assumed ____g/cm3

DIMENSIONS Initial

specimen

Overall

change

Final specimen Specimen

preparation method

Diameter, 𝐷(𝑚𝑚)

Area, 𝐴 (𝑚𝑚2)

Height, 𝐻 (𝑚𝑚) 𝐻0

Volume, 𝑉 (𝑐𝑚3)

WEIGHINGS Initial specimen

(a) (b)

Final

specimen

(c)

Wet soil+ring+tray

Dry soil+ring+tray

Ring+tray

Wet soil

Dry soil

Water

Moisture content (measured)

Moisture content (from trimmings)

Density

Dry density

Voids ratio

Degree of saturation

Height of solids

(a) using moisture content from trimmings

(b) using data from (a) and (c)

(c) data from specimen after test


41

Consolidation test – settlement readings

Increment no. / Date started

Load: ______ kg / Pressure: ________ kPa

Time 𝑡

Gauge

reading

Cumulative

compression ∆𝐻

Strain

𝜀 =∆𝐻

𝐻0

min 0.01 mm mm [%]

0.25

0.50

1

2

4

8

15

30

60

120

240

480

1440



Time 𝑡

Gauge

reading

Cumulative

compression ∆𝐻

Strain

𝜀 =∆𝐻

𝐻0

min 0.01 mm mm [%]

0.25

0.50

1

2

4

8

15

30

60

120

240

480

1440



Time 𝑡

Gauge

reading

Cumulative

compression ∆𝐻

Strain

𝜀 =∆𝐻

𝐻0

min 0.01 mm mm [%]

0.25

0.50

1

2

4

8

15

30

60

120

240

480

1440



Time 𝑡

Gauge

reading

Cumulative

compression ∆𝐻

Strain

𝜀 =∆𝐻

𝐻0

min 0.01 mm mm [%]

0.25

0.50

1

2

4

8

15

30

60

120

240

480

1440


42

Consolidation curve: square root of time fitting method

Consolidation curve: logarithm of time fitting method


43

Consolidation test – log pressure/voids ratio curve

Consolidation test – log pressure/strain curve


44

11. DIRECT SHEAR TEST

11.1. THEORY

The concept of direct shear is simple and mostly recommended for granular soils, sometimes on soils

containing some cohesive soil content. The cohesive soils have issues regarding controlling the strain

rated to drained or undrained loading. In granular soils, loading can always assumed to be drained. A

schematic diagram of shear box shows that soil sample is placed in a square box which is split into

upper and lower halves. Upper section is fixed and lower section is pushed or pulled horizontally

relative to other section; thus forcing the soil sample to shear/fail along the horizontal plane separating

two halves. Under a specific Normal force, the Shear force is increased from zero until the sample is

fully sheared. The relationship of Normal stress and Shear stress at failure gives the failure envelope of

the soil and provide the shear strength parameters (cohesion and internal friction angle).

Box shear tests can be used for the following tests

(1) Quick and consolidated quick tests in clay soil samples

(2) Slow test on any type of soil

Only using box shear test apparatus may carry the drained or slow shear tests on sand. As undisturbed

samples of sand is not practicable to obtain, the box is filled with the sand obtained from the field and

compacted to the required density and water content to stimulate field conditions as far as possible.

Clay soil undisturbed samples may be obtained from the field. The sample is cut to the required size

and thickness of box shear test apparatus and introduced into the apparatus. The end surface are

properly trimmed and leveled. If tests on remolded soils of clay samples are required they are

compacted in the mold to the required density and moisture content.

11.2. AIM

The Shear Box allows a direct shear test to be made by relating the shear stress at failure to the applied

normal stress. The objective of the test is to determine the effective shear strength parameters of the

soil, the cohesion (𝑐′) and the angle of internal friction (𝜙′). These values may be used for calculating

the bearing capacity of a soil and the stability of slopes.

11.3. APPARATUS

(1) Shearbox apparatus for carrying out tests on soil specimens of 60 mm square and 20 mm high

divided horizontally into two halves.

(2) Two porous plates of corrosion-resistant material;

(3) Two perforated grid plates of about the same size in plan as the porous plates;

(4) A loading cap to cover the top grid plate or porous plate;

(5) A calibrated means of applying a vertical force to the loading cap such as a loading yoke;


45

(6) A motorized loading device capable of applying horizontal shear to the vertically loaded

specimen at constant rates of displacement from wich

11.4. PROCEDURE

(1) Place the sample of soil into the shear box, determine the water content and dry density of the

soil compacted

(2) Make all necessary adjustments for applying vertical load, for measuring vertical and lateral

movements and measurement of shearing force

(3) Apply a known load on the specimen and then keep it constant during the course of the test (for

consolidation keep it for a long time without shearing, and quick tests apply the shearing

without consolidation soon after placing the vertical load). Adjust the rate of strain as required

of the specimen.

(4) Shear the specimen till failure of the specimen is noticed or the shearing resistance decreases.

Take the readings of the gauges during the shearing operation.

(5) Remove the specimen from the box at the end of the test, and determine the final water content.

(6) Repeat the tests on three or four identical specimens.

Documents

Laboratory Manual GEOTECHNICS · Dry sieve is performed for cohesionless soils if fines are less than 5%. Wet sieve analysis is carried out if fines are more than 5% and of cohesive