Geotechnical Engineering I

Prof. Devendra N. Singh

Lecture-02
Origin and Definition of Soils

Welcome to the course contents and the reference books as well as the examination which is
nothing unique as per the institute norms.
(Refer Slide Time: 00:36)

So, let us start our discussion on you know because the geotechnical engineering is basically the
mechanics of soils alright. So, it so happens that this is the material and the mechanics you are
aware of all of you have studied, fluid mechanics you have done any course or not yet, during the
semester already finished very good. So, you have done fluid mechanics, you have done solid
mechanics, you have done engineering mechanics.

So mechanics, nothing with the tools if we are using to understand the response of the material.
And in this case, it so happens because we are talking about the geotechnical engineering, our
material is going to be either soils or rocks alright. Now there is a very interesting interplay
between the soils and the rocks. So, it is a good idea to understand what is the origin of the
material alright, all of us have some heritage alright we belong to some place linkage and so on.
So the origin is the first question how soils are formed. So in today's discussion, I will be
focusing on how soils as a material, which is going to be used by civil engineers, particularly
geotechnical engineers alright for various applications. So the materials part is either soils and
rocks, and then I would like to see what forms what, rocks might form soils, which is a normal
process, but it might so happen, that soils might also form rocks.

I hope you are aware of this is it not, so, it is a reversible process. Parents, definitely they give,
you know, they create offsprings. Sometimes it might happen, that offsprings might also create
something, which is look alike parents. So we will talk about the origin how the origin of the
soils has occurred. In the process, we will also try to define what this material is. We will try to
define the material soils alright.

The most important characteristic of this material is it gets formed by some process and then it
gets either transported or it remains at that place only what is known as residual. Now, this is
what is normally known as formation okay. So, the first thing is origin before that comes out to
define this material, how the formation of the soil occurs and this is where we will talk about
several issues like conditions of formation.

Now, formation is a very deceptive term alright it is a incomplete term, it might so happen, that
the formation could be you know a strata itself is also known as formation.
(Refer Slide Time: 04:46)
So, suppose if I say that this is the ground level normally we define the soil surface like this, this
is what is known as geo-micro-bio sphere. So, anything which is existing below the ground level
is our domain alright. So, this is the domain in which a lot of geo is earth. And in this system,
there could be microbial activity, there could be different type of activities which might be taking
might be occurring physical, chemical, biological, thermal, and what not.

So, if I say that the whole strata is a stratified, strata is plural. And stratum is singular. So, each
of these layer, if I say layer alright number 1, number 2, number 3 and so on. Unless you hit,
remind them of the core, these are all the layers layer 1, layer 2, layer 3 alright. So, the strata is
the entire thing, the stratum is layer. Now, as I was saying the formation could be connoting to
please remember these few words in the beginning of the course, then our language becomes
same and I hope you will not have any difficulty later on.

So, if I want to define the layer number 1, this is the formation, clear now, you must have
realized, you know somewhere here we have hills you know Himalayas. And somewhere down
the geographical line, this is you know this would be let us say Hooghly and I hope you
understand why I am drawing this. This is a journey which the entire system is going to traverse,
traverse means travel, what is going to happen here because of various activities, the system is
going to get fragmented.

Those of you who might have gone for trekking in the Himalayas or the hilly terrains, you must
realize a lot of boulders, the big piece of the, you know, rocks they keep coming out. So, that is
one process, which is what is known as weathering, will discuss about this later on. So, if so
happened that the big chunks of the rocks, they get detached from the parent body by some
process, it could be physical, take a hammer, start hammering it, the system gets, you know,
converted into small, small pieces. There could be a chemical weathering taking place alright
because of the chemical actions.

And this could be the fundamental property of the soil or rocks. There could be a combination of
the 2. There could be a thermal activity which might be occurring over here. Temperatures go
very high and the system develops thermal stresses, cracks develop, when the rains come, all
these cracks get filled up with water and these boulders start rolling down alright. So this is what
we actually are going to talk about.

So formation includes how ultimately traveling from point number A to somewhere in the plains
you know what are plains, Gangetic plains. So those of you who are from the central portion of
India, Delhi, UP, Uthrakand not Uthrakand it still goes into the hilly terrain. So these are the
plane areas where the slopes of the you know ground are not much and then ultimately what
happens this thing over comes over and gets into a portion so this is okay.

So this whole journey A to B to C. We are trying to capture 2 3 things which are very important,
how the fragments get form. In other words, how the soils get formed, what is causing them to
come from A to B, this is what is known as a transportation agency.
(Refer Slide Time: 09:19)

So, formation is going to depend upon the cause you know and this cause is going to be mostly
weathering and this weathering could be either physical, chemical, it could be even microbial
alright. Sometime people also call this as a biological and this could be the combination of x, y
and z as well. So this as far as the formation is concerned. The second term which will be
included, which I am going to introduce would be, what causes soils and how they get
transported. In your opinion, what are the transporting agencies, which you might be aware of,
which would move the fragmented portions of the rocks from A to B and B to C, very nice.
So, transporting agencies would be either water yes, in most of the cases, this is water sorry
rains, winds, air nice good, next sorry very good, it could be gravity yes why not, what else. So,
it so happened that something detaches over here because of the weathering action. So,
weathering is nothing but disintegration. This causes disintegration alright. Is this part clear, are
you realizing the material with which you are going to work, is this okay?

So it depends upon all these things. It is a big matrix, water, air, gravity, anything apart from this,
which might be transporting agency. Sorry is living organisms will not transport the soil. Their
role is different. So living organisms, what you are trying to convert to is microbial activity, that
is responsible for creating the weathering process or disintegration of the rocks. Fine, I mean, I
cannot justify your answer.

So, anybody else you think that living organisms, yeah, human beings if you are saying then yes,
that is possible. We are the biggest culprit. Is this okay, so mostly, you know have you have
water, you have air, you have gravity, you have human activities. Another interesting thing over
here is, see it’s a very intelligent material soils. We will talk about this later on, why it is so
intelligent.

Because simple answer is it gives rise to the entire what do you call it, life is this correct or not
life originates from soils. So, we talk about the cause, we talk about the transportation agencies,
there are few materials which get disintegrated, but unfortunately they cannot get transported.
So, we talk about deposition characteristics and normally we term them as residual. Which one is
going to be more experienced, more knowledgeable, more workable all adjectives which you can
think of if you attribute to this.

A person who stays all the time in his or her home or the one who comes out travels leaves
people takes his own decisions, a lot of similarity between what we are studying and what I just
said, look at the process, they were formed somewhere because of some external agencies,
fragmentation took place. The second thing came in the picture transportation, it carried the
material up to a certain distance and this distance could be geological distance of few thousands
of kilometers agreed.
In the process what is going on. All these agencies are giving a lot of rubbing effects, abrasive
effects, you must have seen when you go to the Himalaya you know big big boulders are lying
over there. But as you come down towards let us say Kanpur, Varanasi, Gaya and all these areas.
What happens, all the big boulders are about converted into the small particles sands clear. So,
this in this process of grinding.

The type of grinding which you are going through what IIT Bombay what is happening, you are
becoming more knowledgeable or no whatever it is. So you are getting exposed to different type
of environmental conditions. Is this correct. So a system which gets transported because of the
transporting agencies, keeps everything in its memory. So it is not a inert material. It is not a
dead material. It is a very intelligent and live material alright.

This is another attribute of the soils. So this is memory based. And no wonder why silica is used
as a basic ingredient for designing chips. No?, because the basic constraints of the entire thing is
silica, we will talk about this memory effects in the material alright. I will be using this term
quite a lot. What is memory of the material. There is no other intelligent material like soils in the
history of civilization.

Steel, do you really talk about the memory effect, you talk about how it was formed, do you talk
about how it was deposited, you know, how it is going to behave, how it is going to react. No,
we do not use these terms at all. So that is the difference. And that is why it becomes very
important to study the mechanics of the soils. Is this part clear. So we will talk about all these
things, coming to the second thing, which I was talking about depositional characteristics.

How deposition is taking place, whether the soils are residual or they are transported. So I was
giving a logic, the guy who never came out of the house, he was born in the same house alright.
Attained youth in the same house and became a big person in the same house and is also going to
die in the same house, something of the sort residual. Residual means the disintegration took
place over here.
Unfortunately, there was no transporting agency, transporting agencies nothing like teachers like
us who might be carrying you along with us to some destination. Is this okay? And then
depending upon your fate, you may get deposited somewhere, you may settle down in a
profession clear. So, this is what the positional characteristics are. There are few guys who
remain in the profession for 20 years like me, 25 years, 30 years, they might be getting rotten.

And there are another breed of the people who keep on changing their jobs every now and then.
Another similarity are you getting this point, so these guys are going to have a very different type
of characteristics and memory in their brains. So, this is a very interesting thing which we can
use for designing our structures when we are dealing with the systems which are either
transported or which are residual. Is this part okay?

Because what is my job, my job is to put all of you in order. I told you 2 o'clock, this 2 o'clock,
everybody is there. So I am going to dictate tomorrow with this material as another this material.
Look, this is how you are to behave. Because I am a technologist, I am an engineer, I want you to
behave like this, are you getting this point, and that is what the engineering is all about. That is
what the technology is all about.

So, I have a material clear, I would like to dictate with it, how I will use the principles of
mechanics, which is nothing but the physics and mathematics put together tools. Understand, and
in the process, all this happens, ask any question, I think I have given you the preface of today's
discussion, rest is all bookish. If it is not clear, please discuss. So, this is the preface of today's
discussion. Anything which you like to add.

So, suppose somebody asked you a question introduce yourself, you are asking something. Last
week you remember down the staircase, yes, but suppose somebody says introduce yourself, how
to introduce yourself, this is the introduction of the material clear, now make it a habit wherever
you go in life today onwards. Google, where you are, what type of soil deposits are available
there. You will learn a lot of things.
And if possible, make it a habit to collect some samples also, system retains what has happened
in the past alright. So the memory is what when you came here you are carrying some imprints
of what happened in your childhood alright. When we talk about the engineering issues
associated the material, we will talk about what the material carries in its mind clear, and based
on that it has a tendency to behave to exhibit its response.

So my name is Ankit, Ankit yeah. So microbial weathering takes place. Okay. That is the
interesting thing. I think you should search it out on Google, read some papers if you are really
interested. What microbes produce, any idea, microbes in soil produce gases, and these gases
could be hydrocarbons agreed. So imagine the system is like a control volume where there is lot
of organic matter, I do not know I should not have introduced this word right now.

But I am introducing you can capture all these things. So, this is organic matter, alright. So,
wherever the organic matter is, the bacterial activity is going to have, this is the bacteria inside
and what this bacteria is going to do organic matter provides nutrition, carbon, nitrogen, sulfur
alright like, hydrogen, oxygen and so on. Now, what is going to happen. You have provided
enough food to the bacteria what is going to do.

It is going to be active, what it does, it eats up the material disintegration started. It’s a microbial
or biological disintegration of the material, deterioration of the material. Clear? Alot of Research
and Developments are being done in this context. And those of you are interested in going for
higher studies should note these words carefully. Geotechnical engineering has a lot of potential
for Research and Developments both in the industry as well as academics.

So, my emphasis is to give you more ideas about what's happening in the world today rather than
bookish knowledge alright. So, is this part clear. So, what microbes do, they try to eat up the
system at the same time they might create the system also. So, they act both ways. So, they may
deteriorate or they may upgrade any system. A good example of this is please go and check in on
the net MICP, these are all research ideas.
This is a very interesting area in which lot of research has been done in the area of geotechnical
engineering, soil mechanics, microbial activity and just check it on the net. Is this okay, so what
bacteria does this one of these things processes, if this is happening, I should not bother, but if
this is happening, the system follows the chain this onwards correct. So, this is the microbial
disintegration, fine. I just wanted to provoke your thoughts. What humans are doing.

I want to create a Tajmahal in Bombay. Antalya from where I got all the materials, geo materials
from somewhere in the mines of Rajasthan clear or let us say from Orissa or some south you
know. There are a lot of stones which are available in Kadapa region. So, humans also transport
the material. A beautiful example of this would be reclamation. So, most of the islands which are
being created all over the world.

How many islands have been created last 2, 3 years. Look at the geography of the world is not
stationary. You know, when we were kids, we used to use the same book for 30 years, Atlas.
Now that was happening. Atlas keeps on changing every month yesterday, something happened.
It is a good example you know so what has happened. The geography is going to change.

So South China see what is happening. China is expanding. Next time when you go to Singapore
when you are landing, just sit on the seat number A, or last one H and tip down. What we will
see a lot of activity going on in the ocean. What do they do. They bring soils from different
places, they dump them over there, and they are creating islands. We have got the answer to your
question. So humans are also becoming extremely notorious in transporting the soils.

But this also how the civilization is, how many islands and has constructed last 5 years. All
strategic. check it on net. You understand, so the geographical boundaries are changing why,
because it is my wish I would like to bring material from somewhere and dump it somewhere.
The same process I am following look at this, the material was created by human activity by
minute, I got it in the barges over the pipelines or whatever, I transported it and I deposited it
agree.
So what nature was doing in millions of years, I have done it in 5 years, 10 years. Palm islands,
Pearl islands, world islands is a beautiful example of creation of land. Okay, so human activities
associated let us say with the land reclamation, search it out more yourself about this thing. This
itself in the formation of rock, shall I add manmade this is okay, microbially induce calcite
precipitation.

Now because of this what is coming out of the bacterial secretion, the system gets upgraded,
formation of rock takes place. I can use it for my different applications. Very good, good
question. Yes, sir how a chemical can be used? suppose if I go somewhere on the hill iterance
and I carry say 100 liters of sulfuric acid, concentrated 5 molar sulfuric acid and I will pour it on
the system what will happen, chemical interaction clear.

So you are adding something chemically to create disintegration or weathering of the material
clear. So, this could be by hammering as I said physical, it could be chemical you add some
chemical compounds in it, have you ever seen any blasting which was done in any of the projects
you know in the rocks. So, what do they do. They drill holes, they put chemicals and then they
wait for 24 hours and what happens? Bhoom, clear.

The rock becomes disfragmented, is the chemical induced weathering of rocks for making
highway projects. Is there any natural chemical phenomenon of weathering. Good question.
Have you heard about arsenic oozing out of soils in the western eastern part of the country. This
is one of the chemical processes which might be bacteria driven. If you see any acid, acid range
pH it will be in less than 4.5 but go to the genesis industrialization and too much of
industrialization means that most of your industries are emitting SOX, NOX, COCs

So, all these things will be the environment and then what happens. So, when clouds forms this
gases will also get trapped inside the clouds okay. So when it starts precipitating rains
precipitation means rains, rains when start precipitating that SO2, NOx, nitric oxide anything will
get mixed with water and it will turn it into acid, weak acid yes weak acid. So, it will get
precipitated on the rocks like if possible such kind of rain happens in the region of Himalayas.
So the kind of chemical that precipitated over there might try to might trigger the disintegration
of the rocks correct. Any other example, which comes to mind is this okay, you have understood.
Acid rains are a good example of how human activities are going to create more and more
chemical weathering of the system, including the buildings that you have constructed.
(Refer Slide Time: 29:12)

So let us start now with the conventional discussion. Let us say how to define soils, you will be
surprised to know that this is the material which has several definitions. You know why. So,
everything is a material. So, when I say define soils, this boy is not very good, very casual
remark. Oh, he is excellent is a 10 pointer whatever. You say like this you define a person by
using some attributes.

In this case, what happens is most of the attributes are a function of so if so happened that these
functions these are the functions of the profession you understand it is such an interesting
material. What is the meaning of this? what is your name? say your name at least Ashish sorry. Y
you can’t follow my words or what. So, the definition of the material depends upon the attributes
which are profession dependent.

How would you complete the statement? Depending on what the soil used for we assess the
properties, the function of the soil, not the function of the soil, I said the definition of the
material depends upon the attributes and one of the attributes is the profession in which you are,
what is your hobby, what do you do. Apart from that, poetry apart from that so suppose if you
are a pottery maker, many people who do sculptures is it not.

How do you define soil, by the way, most of my research on cracking characteristics of soils, you
know, my guru was the guy who came for mood indigo, who was doing pottery making. I called
him in the lab. And then after that I might have guided I do not know 2-3 phds and several
papers which I have written on cracking characteristics of soils and my question to him was that
why your pots do not crack.

Because this is the answer, which BCCI was looking for. And I was a consultant to BCCI, I hope
you are aware of, before 2011 World Cup, I made their pitches, I gave them a recipe. So my big
question in the mind was that let me create pitches which will never crack. Of course, I spinners
will not be very happy with me. So why I am telling you this is the story is because if I am in this
profession, what would I like.

I would not like any system to crack. But just now what I had said if I am creating pictures a
spinner would like this pitch to crack to in the third hour of the match why. Then we have so
many in our team who will go and finish the game in 2 days. You are getting the point. The
material is defined by the attributes which are mostly dependent upon the profession. So, you
might be a potter, sculptur or you might be a you know a player.

And what type of games you use soils and what type of sports you use clays, soils or what,
number 2 yes. okay. See my connotation is more on the turf. Very nice good in Lawn Tennis,
how many types of tennis you have, varieties why how many types of courts you have. Yes, now
you would link the subject with a practice. Are you getting the point. So why do they have these
4 grand slams.

Why they want to test whether this guy is going to be a winner on all types of turfs or not
remember. So you have clay courts clear, you have grass courts also, which one is grass courts?
Wimbledon. Excellent, you are right. So, that means depending upon what sports you are playing
and what are the requirements, you can play with this material you can define the material, is this
okay, football is not a very direct answer.

It should be either mostly tennis where the ball impinges and then you must have studied in your
mechanic course reverse English forward English, all those things you have heard or not Halide
Resnick 10 +2 Physics. No swing, why the wall swings, late cutter, in-cutter, all these things are
derived by the material properties. If I can control over here, everything the response is going to
be different. Understand. There is nothing but the engineering properties which I have to
modulate and the pictures are ready.

So tennis court is a good idea your cricket which is a very good idea, anything else apart from
that, basketball not going to be of much because the basketball you do not impinge the ball
intentionally on the ground when you are playing. Of course we are bouncing all is fine. So
anyway so this is where agriculturist, it is a big profession is not farmers over the country how
they check soil.

They do not have a laboratory, what do they do. They will just touch the soil, they will rub it, add
some water again rub it smell it and they will tell you whether this type of soil is good for this
particular produce or not. Why, why they are so experienced. I mean they must be checking
some attributes. For them the requirement of the soil is different fine. Suppose I am a florist you
know what is florist level guy was producing flowers.

They are very particular about you know a type of soil which should be used for creating a
certain breed of flowers is a big business. Apart from this any other profession quickly tell me
what are the other professions where you use soils sorry yeah. Construction okay. So we will
keep ourselves we will place ourselves engineering oh electronics, not in the soil form so is
expected form of let us say silica, which is one of the constituents of the soils.

So, I will not put it in this matrix because of this reason alright. We are talking about right now
natural systems and professions. Okay, but your answer is good. At nano level we can think of
yes. Any other profession, sorry. Mining will come in engineering, S and T, let us say science
and technology, beauticians, skincare, where do they use soils you never bothered about it you
know Bargavi. Bargavi yes, please talc okay, nice so.