Basic soil characteristics

1. BASIC CHARACTERISTICS OF
SOILS
(LECTURE 1)
SOIL MECHANICS & GEOTECHNICAL
ENGINEERING (CVE 3304)
FACULTY OF ENGINEERING AND
QUANTITY SURVEYING
M s N u r u l A i n

2. Learning Outcome
• At the end of this lecture, students should be able to :
Understand the definition of soil mechanics and geotechnical engineering
Describe the nature of soils
Determine the type of soils
 Analyse on particle size analysis, properties of fine grained soils and
coarse grained, mechanical analysis of soils for soil classification
PO1: Apply acquired fundamental knowledge of science and
engineering to solve complex engineering problems with emphasis on
field of civil engineering

3. Introduction Soil Mechanics and Geotechnical
Engineering
• Soil : Defined as uncemented aggregate of mineral grains and
decayed organic matter (with liquid and gas) in the empty
spaces between the solid particles.
• Soil : Used as a construction material in various civil
engineering projects and it support structural foundations.
• Soil : Civil engineers must study the properties of soil such as
its origin, grain size distribution, ability to drain water,
compressibility, shear strength, and load bearing capacity.

4. Introduction Soil Mechanics and Geotechnical
Engineering
• Soil mechanics : Branch of science that deals with the study of the
physical properties of soil and the behavior of soil masses subjected to
various types of forces.
• Soil engineering : The application of the principles of soil mechanics to
practical problems.
• Gerotechnical Engineering : Defined as the subdiscipline of civil
engineering that involves natural materials found close to the surface of the
earth. Includes the application of the principles of soil mechanics and rock
mechanics to design of foundations, retaining strutures, and earth
structures.

5. Introduction to Soil Mechanics and Geotechnical Engineering

6. Introduction to Soil Mechanics and Geotechnical Engineering
Soil is a natural body
comprised of solids
(minerals and organic
matter)
Soil formed over a long
period of time
Soil is formed from the
weathering of various
types of rocks and
minerals.
The surface rocks break
down into smaller pieces
through a process of
weathering and then
mixed with organic matter
Organic soils are formed by
the decomposition of plants
and animals residue

7. Introduction Soil Mechanics and Geotechnical
Engineering
Weathering : Weathering is process of breaking down rocks by mechanical
and chemical process into smaller pieces.
• Mechanical weathering (Disintegration of rock) : May be caused by
expansion and contraction of rocks from the continuous gain and loss of
heat, resulting ultimate disintegration.
• Freezing and thawing may widen the crack in rock by expansion of
moisture in the crack.
• Root of vegetation may penetrate rock pores or existing cracks to further
increase their sizes.
• Abrasive action due to mass movement that help disintegrate of rocks are
glacier ice, wind, the running water of streams and rivers, and ocean
waves.

8. Introduction Soil Mechanics and Geotechnical
Engineering
• In chemical weathering (Decomposition of rock) : The original rock
minerals are transformed into new minerals by chemical reaction that take
place from oxidation, hydration and carbonation.
• Oxidation is an agent in the decomposition process whereby oxygen ions
combinewith some minerals in the rock which subsequently decomposes.
• Carbonation is a form of decomposition where CO2 and water form
carbonic acid which decomposes minerals containing iron, sodium,
calcium.
• For example, clay minerals are product of chemical weathering of feldspar,
ferromagnesians, and micas that provide the plastic property to soils.
• Weathering process occurs almost in similar manner as for igneous rock,
sedimentary, and metamorphic rock respectively.

9. Nature of Soils
• Residual soils are formed from the weathering of
rocks and practically remain at the location of
origin with little or no movement of individual
soil particles.
• Residual soils can include particles having a wide
range of sizes, shapes, and composition
depending upon the amount and type of
weathering and the minerals in the parent rock.
• The rate of weathering is generally greater in
warm, humid regions than in cool, dry regions.
• For example, limestone is particularly vulnerable
to the effects of solvents and weathering, forming
irregular and highly plastic residual soil.
Disintegration of limestone may cause sinkholes
and caves. Thus, detailed site investigation is
needed when limestone formation is detected on
site. Profile for residual soil area, indicating stages of
transition from rock to soil

10. Nature of Soils
• For example, limestone is particularly vulnerable to the effects of solvents and weathering,
forming irregular and highly plastic residual soil. Disintegration of limestone may cause sinkholes
and caves. Thus, detailed site investigation is needed when limestone formation is detected on
site.
• One of the solution to limestone problem is by bridging of the site with properly designed slab so
as to “cap” the site in floating manner.
• Sandstone may form a weathered surface that is generally plastic, when mixed with clay soil may
be unstable and with time may convert to a clayey and plastic material.
• This may lead to poorly resistant to an accelerated weathering process. One of the solution is by
soil stabilization using chemical stabilizer which may prevent further disintegration to occur.

11. Nature of Soils
• Transported soils are those that have formed
at one location (like residual soils) but are
transported and deposited at another
location by one or more of the transportation
agencies, such as water, glacier, wind, and
gravity, and deposited.
• Soil may be transported in the form of
suspended particles or by rolling and sliding
along the bottom of the stream.
• Soils that are carried and deposited by rivers
are called alluvial deposits.
• If coarse and fine-grained deposits are
formed in seawater areas, then they are
called marine deposits.
Process of water erosion, transportation, and deposits

12. Nature of Soils
• Organic layer : Organic debris, partly decomposed
• Top soil : Mineral particles mixed with organic material
• Subsoil : Compounds draining from above accumulate
• Parent material : Partly weathered rock
• Bedrock : Hardest layer of rock.

13. Soil Classification
• Purpose is to classify the soil into a group according to the soil behavior and
physical features.
• Soil classification mainly depends on origin and size of particles within the soil
• Soil can be classify into two categories : non cohesive soil and cohesive soil.
• Non cohesive soil :
>> The soil particle are not sticking to each other. (Loose sand)
>> Known as coarse grained soil
>> Water are easy to penetrate into these type of soil because of its
hollow particles but gives up water easily.
>> E.g : Gravel and sands

14. Soil Classification
• Cohesive soil :
>> Soil particles are closely integrated and stick together. (Dense
sand)
>> Known as fine grained soil
>> Has a high level of moisture content since these soil not drain out
water easily
>> Eg : Silt and clay

15. Soil Structure
Coarse grained soil structure Fine grained soil structuree
More pore
space
Less pore
space

16. Soil Classification
Difference between gravel, sand, silt, and clay

17. Soil Classification
Particle Size Distribution Test
• The determination of the size range of particles present in a soil, expressed
as percentage of the total dry weight.
• According USCS, two methods generally used to find the particle size
distribution of soil are:
>> Dry sieve analysis test : For particles sizes larger than 0.075 mm
in diameter. (coarse grained soil)
>>Wet sieve analysis test : For particles sizes smaller than 0.075
mm in diameter. (fine grained soil)

18. Soil Classification
Dry sieve analysis test conducted in the laboratory :

19. Soil Classification
Particle size classification according to :

20. Soil Classification
Sieve analysis test :
• Consists of shaking the soil sample through a set of sieves that have
progressively smaller openings.

21. Soil Classification
Dry sieve analysis test (USCS):
• Any soil particles that retained (not passing) through 4.75mm or sieve no
4, then it is classify as gravel.
• Any soil particles that retained (not passing) through 0.075 mm or sieve no
200, then it is classify as sand.
• Soil particles that passing through 0.075 mm sieve classified as silty and
clay.
• The soil sample shaken in the shaker for about 10 to 30 minutes to fairly
distributed according to the grain (particle) size.
• The sample will be collected from every sieve and the data will be
tabulated to analyse particle size.

22. Soil Classification
Sieve Analysis test:
• Procedure to analyse based on sieve test :
1) Determine mass of soil retained on each sieved (i.e : M1, M2, ……
and in the pan.
2) Determine percentage of soil retained on each sieve
3) Determine the cumulative percentage of soil retained on each
sieve.
5) Determine the percentage of soil passing the ith sieve (or percent
finer).

23. Soil Classification
Sieve Analysis test:
• Procedure to analyse based on sieve test :

24. Soil Classification
Sieve Analysis test:
Log scale

25. Soil Classification
Sieve Analysis test (Particle size distribution curve)
• A particle size distribution curve with logarithmic scale on X-axis is used to determine the
following parameters for a given soil:
>> Determination of effective grain size (D10) : Diameter in distribution curve
corresponding to 10% finer.
>> Determination of uniformity coefficient (Cu) : This parameter is defined as
Cu =
𝐷60
𝐷10
𝐷60 = Diameter corresponding to 60% finer.
>> Determination coefficient of gradation (Cc) : This parameter is defined as
Cc =
𝐷30
2
𝐷10 𝑥 𝐷60

26. Soil Classification
Sieve Analysis test (Particle size distribution curve)
>> Determination Sorting coefficient (So) : Measure of uniformity and is generally
encountered in geologic works. Expressed as
So =
𝐷75
𝐷25
• Hence, the percentages of gravel, sand, silt, and clay-size particles present in a soil
can be obtained based on particle size distribution curve.
• For example, according to the Unified Soil Classification System, the soil can be
classified as below:

27. Soil Classification
Sieve Analysis test (Particle size distribution curve)
• Other than particle size, type of distribution curve of various size of particles also can be
obtained.
• There are three major type of distribution curve exist which are :
>> Well graded
>> Gap graded
>> Uniform graded
Size (mm) % Finer Soil Classification
76.2 100
4.75 100 0% Gravel
0.075 62 100 – 62 = 38% of sand
Pan 62 62 – 0 = 62% of silt and clay

28. Soil Classification
Sieve Analysis test (Particle size distribution curve)
•

29. Shape Particle
• The shape of particles in a soil mass also important because it has significant influence on
the physical properties of a given soil.
• Particle shape can be divided into three major categories :
1. Bulky shape
2. Flaky shaped
3. Needle shaped.
• Bulky particles are mostly formed by weathering of rock and minerals. Geologist
normally used such term as angular, subangular, rounded and subrounded to describe the
shapes of bulky particles.

30. Particle Shape
Shapes of bulky particle

31. Shape Particle
• Flaky particles have very low sphericity. These particles are predominantly clay minerals.
• Needle shaped particles are much less common than the other two particles types.
Example of soils containing needle-shaped are some coral deposits.

32. Shape Particle
• Flaky particles have very low sphericity. These particles are predominantly clay minerals.
• Needle shaped particles are much less common than the other two particles types.
Example of soils containing needle-shaped are some coral deposits.

33. Tutorial 1
1. Following are the results based on sieve analysis test conducted on the soil sample to
classify the soil :
Sieve no Openings (mm) Mass retained (g)
4 4.75 0
10 2.00 14.8
20 0.85 98.0
40 0.425 90.1
100 0.15 181.9
200 0.075 108.8
Pan

34. Tutorial 1
(a) Plot the grain size distribution curve.
(b) Extract and identify the percentages of soil type existing on the soil sample tested
(c) Determine the effective size, the uniformity coefficient, and the coefficient of curvature.

35. Thank you