GEOLOGY FOR CIVIL ENGINEERS
CHAPTER 1
Introduction
All civil engineers, dealing with foundations of a structure and the works related to dams, tunnels, stability of earth
slopes etc., should have a fair knowledge of the geography, climate, type of soil and geology (rocks formation) etc., of
the regions they are working in. Similarly those working in different parts of India should have a general knowledge of
the general geology of India and a special knowledge of the place where they are working. It is not necessary that all the
civil engineers in India should know the detailed geology of all the places of the country, which a professional geologist
should definitely know.
(DAMS)
(TUNNEL)
(STABILITY OF EARTH SLOPE)
In the important projects like a dam site or the foundation of an important bridge where we have to deal with rocks, it is
necessary that a detailed geological survey should be made by an engineering geologists, not an engineer. However, it is
also very important that an engineer should understand the geologist’s report and the terms he uses. One of the
important points any geological report will contain is the geological history of the formation of the rock at the site.
Hence, in this chapter we will briefly deal with the historic geology only to make ourselves familiar with the terms and
their meaning as used in geological reports. We need not go for a detailed study of historical geology.
1.2 A Short History of Earth and Division of Geological Time
The earth (which is about 6370 km in radius) is the part of the solar systems along with the other planets. It rotates
around the sun at a mean distance of 158 million kilometers (Thus the speed of earth around the sun is about 1800 km
per minute and the revolution speed of the equator will be around 1660 km an hour). It is believed to have been formed
some 4500 million (4.5 billion) years ago from a hot ball of molten mass perhaps separated from the sun. The Earth’s
present structure is shown in Figure 1.1. Only the curst of the earth must have taken a long time to cool down. Even
after 4.5 billion years of cooling the thickness of crust is only about 40 km, below which it is still hot magma.
Figure 1.1 Structure of the earth. Earth’s crust floating on magma. (1) Crust, (2) Magma, (3) Core
(STRUCTURE OF THE EARTH)
As described by Bill Bryson, if we imagine the 4500 million years of the earth’s history into a normal “24 hour day”
starting at zero hours at midnight as represented in Figure 1.2 then each minute will be about 3.125 million years. As
shown in Figure 1.2.
Figure 1.2 The 4600 million year’s history of our earth depicted as 24 hours. (1) 4:00 am single cell appears, (2) 20:30
hours sea plant appears then all sorts of plants and animals, (3) Humans appear about “one minute” before the end of
the day.
Life on earth began as a single cell organism only at about 4 a.m. early morning. There was no development for another
sixteen hours till 20:30 hours. In the night at 20:30 hours the sea plants appeared. Soon the jelly fish also appeared. It is
only just before 22:00 hours in the night after a long period and towards the close of the day that plants began to grow
on lad. Soon the land creatures appeared and due to 10 minutes of suitable weather the earth covered with rich
carboniferous forests (which was later converted to coal we now mine). Dinosaurs came at about 23:00 hours and ruled
the earth for about 45 minutes. Mammals appeared twenty one minutes before the midnight. The first form of humans
appeared only “one minute and 17 seconds” before the end of the day, midnight. Present civilized form of the humans
appeared only by the Ice Age which was at its height around 16,000 BC only. It can be seen that we, the civilized human
beings, who use written languages, had been on this earth for a very-very short time in the history of the earth. Thus the
lifespan of all of us is less than a moment compared to in the history of the earth! On the other hand the stone you see
on the road would have existed on this earth for the past many millions of years.
The above short description can make us feel how the crust of the earth in which we are interested in, must have
undergone many disturbances during the last 4.5 billion years. It must have shrunk on cooling (the interior of the earth is
still a liquid or plasma as shown in Figure 1.1) and undergone a lot of stresses and strains. Geology is the study of this
small crust of the earth. This book on engineering geology deals only with geology as applied to civil engineering.
1.3 Geological History (Time Scale and Rock Scale)
In Chapter 3, we will study that there are three types of rocks, the igneous rocks derived from magma, the sedimentary
rocks derived from various inorganic and organic sediments and metamorphic rocks, metamorphosed under intense
heat and pressure. Because the formation of igneous and metamorphic rocks has taken place under the intense heat,
fossils of plants and living things can exist only in the sedimentary rocks. Hence two scales are used to indicate the
geologic history or rocks. First is the “time scale” called era, based on the age of the earth or periods of the appearance
of large animals and plants as indicated in section above. The second is the “formation scale” also called the “rock scale”.
(FOSSILS OF PLANTS)
(FOSSILS OF LIVING CREATURES)
(IGNEOUS ROCKS)
(SEDIMENTARY ROCKS)
(METAMORPHIC ROCKS)
It was proposed at the end of the eighteenth century by William Smith, who discovered that groups of sedimentary
geological strata were characterized by the preservation of particular fossil organisms of various creatures in them. As a
civil engineer needs only to understand the geological report, we need only to familiarize ourselves with the geological
terms and their meanings. As they do not conduct geological surveys they need not learn how to identify various fossils
to determine the formation of the sedimentary rocks. Geologists on the other hand should have a thorough knowledge
of this subject.
It is of interest to us to know that even though the sedimentary rocks from only 5% of the total volume of the
lithosphere (total crust of the earth) the rest being of igneous rocks, 75% of the exposed rock area of the earth’s surface
is made of sedimentary rocks. Hence the formations scales based on fossils become very important in our geological
investigations.
1.4 Division of Geological Scales
As explained above we have to distinguish between two scales used in the geological history, namely the “time scale” or
era which is related to the arrival of animals and plant life on earth (as described in Section 1.1) and the “formation or
rock scale” based on the fossils of the minor organisms like starfish, shells, etc. In the geological reports these scales are
further divided into the following subdivisions.
1. Time scale is divided into:




Era
Period
Epoch
Age
2. Formation scale is divided into:





Groups (like Mesozoic)
System (like Triassic)
Series (like upper Triassic)
Stage (like Carnic)
Zone (Tropitos)
It may be interesting to note that fossil humans appear only in the time scale called Pleistocene just below the recent
system. This is also the glacial age of the northern region of the world and formation of Indo-Gangetic plain in North
India and laterites of Malabar. (Table 1.1)
Table 1.1 Geological/Time scale sedimentary rocks
Group - Era
1. Quarternary
2. Tertiary or Cenozoic
3. Secondary or Mesozoic
4. Primary or Palaezoic
System
Recent
Pleistcene
Pliocene
Miocene
Oligocene
Eocene
Cretaceous
Time in 106
years
(1)
(8)
(25)
(38)
(65)
(140)
Jurassic
(200)
Triassic
(240)
Permian
(290)
Pennsylvanian
(350)
Devonian
(410)
Silurian
Ordovician
Cambrian
Pre-cambrian
(544)
(505)
(605)
(2500)
Comments (Fossil)
Living beings man appears, many mammals die
during the glacial periods
Mammals, flowering plants dominant.
Giant reptiles and ammonites disappear at the end.
Flowering plants become numerous
Ammonites abundant. First birds, flowering plants
and sea urchins
Ammonites, reptiles, and amphibian abundant. Arid
climate.
Trilobites disappear at the end. Many non-flowering
plants; first the reptiles appear.
Abundance of corals, brachiopoda first amphibians
and lung-fishes.
Graptolites disappear at the end first fish, probably
first land plant.
Abundance of trilobites, and graptolites.
Abundance of trilobites.
5. Pre-cambiran or
Soft-bodied animals and plants.
Proterozoic
6. Archaean or Axoic
Archaean
(3600)
Lifeless
6
(Age of the earth is about 4500x10 years life appeared first during the pre-cambrian time. Figures shows the lapse of
time (in millions of years) from the beginning of particular era to the present).
(AMMONITES)
(TRILOBITES)
(BRACHIOPODA)
(GRAPTOLITES)
1.5 Historical Divisions of Geological Formations in India
As can be seen from Table 1.1, in geologic dating the history of the earth is divided into six major divisions. These major
divisions are then divided into many subdivisions.
1.6 Geologic Formation and Series
The word “formation” is a group of rocks composed of similar materials displaying common characteristic formations.
They are named commonly by the name of the locality where it is most prominent or first observed. The rock formation
in India has been divided into nine systems which is described in Section 1.7.2 below. Details of these are given in Table
1.2 while Table 1.3 shows the division of geologic time in American practice.
Table 1.2 Major geological formations of India
Recent
Pleistocene
Recent alluvia, Sand dunes, Soils
Older Alluvia, Karewas of Kashmir and Pleistocene river
terraces etc.
Siwalik, Irrawaddy and Manchhar Systems, Cuddalore,
Warkilli, and Rajamahendri sandstones
Muree and Pegu systems, Nari and Gaj series
Ranikot-Laki-Kirthat-Chharat series
Deccan traps and Intertrappeans
Cretaceous of Trichinopoly, Assam and Narmada valley,
Guimal and Chikkim series, Umaia beds
Kioto limestone and Spiti shales, Kota-Rajamahal and
Jabalpur series
Lilang system including Kioto limestone, Mahadeva and
Panchet series
Kuling system, Damuda system
Lipak and Po series, Talchir series
Muth quartzite
Himalayas
Himalayas
Haimanta system; Garbyang series
Cuddapah and Vindhyan systems, Dogra and Simla Slates,
Martoli series
Dharwar and Aravalli systems, Salkhala, Jutogh and Daling
Series, Various gneisses
Mio-pliocene
Oligo-miocene
Eocene
L. Eocene : Up creataceous
Cretaceous
Jurassic
Triassic
Permian
Carboniferous
Devonian
Silurian
Ordovician
Cambrian
Pro-cambrian
Archaean
Table 1.3 U.S. Division of Geological Time
Cenozoic era (or period)
Quaternary
Recent Pleistocene 1.0
million or Glacial
Tertiary
Cretaceous
Jurasic
Secondary or Mesozoic era
Triassic
Permian
Pennysylvanian
Mississippian
Carboniferous
Primary or palaeozoic era
Devonian
Silurian
Ordovician
Cambrian
Proterozoic era
Kaweenawan
Huronian (Animike)
Archeozoic
Tiiskaming
Keewatin
Note: Precambian – (Primary or palaeozoic era, Proterozoic era, Archeozoic)
Approximate age in years
60 million
200 million
350 million
520 million
3 billion
1.7 Physiographic and Stratigraphical Divisions of India
It is common to divide India into two types of divisions, physiographic and stratigraphy divisions as described below:
1.7.1 Physiographic Divisions of India
On the basis of the natural features which we call physiography (or topography) India can be divided into three major
physiographic divisions as shown in Figure 1.3. Each division has its own distinguishing characteristics.



Indian peninsula
Indo-Gangetic alluvial planes
Extra peninsula (Himalayan region)
The peninsular India is very old, one of the oldest regions of the world. The extrapeninsular region which is the Himalyan
resions has been active till recently and is even now subjected to many earthquakes. The Indo-Gangetic plane was
formed due to sagging of the land during the creation of the mountains of the extrapeninsular region. The rocks in this
region are considerably below the present ground level. The depression was later filled up with sediments of the mighty
rivers.
1.7.2 Stratigraphical Division of India
We are interested in rock formation. According to formation of bedrocks India is divided into the following nine
stratigraphical divisions as shown in Figure 1.4. They are also called systems. These are classified according to their age
as follows:
1. The Archaean sytems (granites, mostly consist of gneisses and schists, The very ancient unit)
2. The Cuddapah systems (Quartzites and shales)
3. The Tertiary systems (extra-peninsular sandstone, limestone)
4. The Alluvial system (the most recent system)
5. The Vindhyan system (limestone and shales)
6. The Palaeozoic system (dolomites, shales, and quartzites)
7. The Mesozoic system (Shales, limestones, and quartzites)
8. The Gondwana system (Sandstones and shales)
9. The Deccan trap system (basalt)
Note: Nowadays the age of rock can be determined by the radioactive age determination methods. The oldest rocks so
far known in India was found in Mysore and is believed to be 3000 million years old. The recent deposits of monazites in
Kerala and granites of Eastern Ghats are about 500-700 million years old.
1.8 Examples of Descriptions in Engineering Geology
The geologic description of damsite in the Kaachehi district of the state of Guarat is given in a report as follows: “The
foundation strata are composed of silty and sandy type of rocks of khari series of Miocene age”. From such a description
with reference to Table 1.1 we can first guess the age of the formation. Other general properties can be inferred from a
knowledge of properties we have already found in other places of the khari series. This preliminary geological
information is very useful to the geologist and civil engineer for the preliminary study of a civil engineering project and
planning of further detailed investigation into boreholes. Further field surveys, detailed borings and tests will be
necessary to get detailed engineering data for design and planning of the construction.
1.9 Plate Tectonics and Continental Drift
Plate tectonics means plate building. Till recently geologists could not say how the present continents were formed. It
was known only around 1960, when Alfred Wagener proposed the theory of continental drift. Briefly the theory is as
follows.
Till about 200 million years ago in the first stage of the development of the continents, all the land masses of the world
existed together as a jointed mass or super continent called Pangaea floating on the magma as shown in Figure 1.5. In
the second stage this broke into two segments plates namely Laurasia (consisting of North America, Europe, and Asia as
one mass) and Gondwana land (consisting of South America, Africa, Peninsular India, Austria, and Antartctica). In the
third stage each of these continents drifted to the present or existing positions with India joining the Europe and Asia
plate (Figure 30.1 of Chapter 30 shows the drift of India and Sri Lanka from the south pole to the Europe and Asia plate).
The joining impact created the Himalayas. The portion between the peninsular India (which existed for a long time back
with Africa) and Himalayas was later filled with alluvial soils thus forming the present land India, India is thus of unique
origin.
At present it is believed that the crust of the world is broken into seven major plates and twelve minor plates as shown
in Figure 1.5. The seven major plates are the Pacific Plate, North American Plate, South American Plate, Eurasian Plate,
African Plate, Australian Plate, and Antarctica Plate. The Pacific plate is mostly an ocean crust while other plates consist
of both oceanic and continental crusts.
It is also interesting to note that most of the severe earthquakes of the world have taken place along the faults or
junctions of the plates, denoting that the movement of these plates are still on. The ring of fire regions consisting of the
western coasts of North and South America, the islands situated east of Asia and those near Australia, all taken together
are sometimes referred to as the Pacific Ring of Fire as shown in Figure 1.6. (Note how Japan and Turkey the two
important earthquake regions of the world lie on the junctions of the plates.)
Figure 1.5 Continental drifts and formation of present continents. (a) Joined mass Pangaea (b) Laurasia and Gondwana
land (c) Formation of present continental rafts floating on the magma (d) The seven major plates (continental rafts).
1.9.1 The Theory of Isostasy
This theory states that there is a state of balance between the large high areas on the earth’s crust such as the mountain
ranges on the one hand and the adjacent low lands (plains) on the other as shown in Figure 1.7
The Himalayas and the deep Indo-gangetic plains are quoted as examples of this theory. Borings into the plains of North
India for nearly 100 m (300 ft) below the sea level has shown that the great land adjacent to the Himalaya has been
subsiding ever since it was loaded with deposits from the foot of the mountains. It is believed that the deposit has still
not reached stability and is still slowly sinking, leading to movement and earthquakes in this region.
1.9.2 Movements between Plates
It is believed that the plates can move between themselves just like ice blocks floating on ice water as shown in Figure
1.8 producing various forces between the plates causing earthquakes.
1.10 Summary
This chapter gives a short account of the geological history of earth, the rocks, and deposits. Geologists have divided the
geological formations of India into different group systems and series. These usually referred to in the “geological survey
reports of projects” that geologists prepare for a site used for a civil engineering project. It is understood that only a
person trained in geology (geologist) should conduct the geological survey and try to interpret the rock formations in a
place. A civil engineer should understand the history of the formation as described by the geologist and its general
characteristic from the geological report. He should have thorough knowledge of the engineering characteristics of the
rocks so that he can carry out the design and construction of the project. A short note on the evaluation of the present
continents and especially the Indian subcontinent is also given in this chapter.