Geology introduction note

1. ECE 2302
ENGINEERING GEOLOGY
TOPIC-1
INTRODUCTION

2. COURSE SYLLABUS
1. Introduction to Geology
2. Site Investigations
3. Engineering Properties of Soils and Rocks
4. Earthquake and Geophysics
5. Ground Subsidence and Slope Stability

3. Introduction to Geology
• Introduction to Geology and its relevance to Civil
Engineering
• Formation, nature and Types of rocks
• Minerology
• Structural Geology
• Weathering

4. Geology and its relevance to Civil Engineering
 Geology is the science of rock, minerals, soils, and subsurface water, including the
study of their formation and behavior.
 Engineering geology is the branch that deals with the application of geology principal
to engineering works.
 Unlike geotechnical engineers, whose training is in civil engineering,
engineering geologists have a background in geology (work include mapping,
describing and characterizing rocks and soils at a construction site, accessing stability
issues such as land slides and appraising local seismicity and earthquake potential).
 In other words, engineering geologists provide crucial information about the
site that geotechnical engineer will use in analysis and design.
 Its important that geologist have some understanding of engineering and
engineer have some understanding of geology

5. Geology and its relevance to Civil Engineering
 Geology is the science of rock, minerals, soils, and subsurface water, including the
study of their formation and behavior.
 Engineering geology is the branch that deals with the application of geology principal
to engineering works.
 Unlike geotechnical engineers, whose training is in civil engineering,
engineering geologists have a background in geology (work include mapping,
describing and characterizing rocks and soils at a construction site, accessing stability
issues such as land slides and appraising local seismicity and earthquake potential).
 In other words, engineering geologists provide crucial information about the
site that geotechnical engineer will use in analysis and design.
 Its important that geologist have some understanding of engineering and
engineer have some understanding of geology

6. Geological Cycle
Geological CYCLE
 Land: erosion and destruction of
rocks
(Weathering)
 Sea: Deposition and forming new
sediments
 Underground: New rock
formation and deformation
(Petrology )
 The earth is an active plane in a constant state of change
 Constant state of change is Geological Process (Cycle of
Geology)
 Geological Process continually :
 Modifies the earth surface ,
 Destroy old rocks (Weathering of rock to form
soil)
 create new rocks (Petrology)
 Add complexity to ground conditions (Ground
Movements
 The geological cycle includes many
processed acting simultaneously
 The most important begins with molten
magma from within earth crystallizing
into rock, the continue with rock being
broken down into soil and then soil
being converted back into rock

7. Where does Geological Cycle occur
 Land: erosion and destruction of rocks
(Weathering)
 Sea: Deposition and forming new
sediments
 Underground: New rock formation
and deformation (Petrology ), earth
movement (Seismology)
Geology and its relevance to Civil Engineering
Significance to Civil
Engineering
 All civil engineering
works are caried out
on the ground.
Properties of rock and
soils are significant
 Unstable ground does
exist
 Unforeseen ground
condition

8. (a) ROCK FORMATION AND TYPES
Types of rock
Depending on the Origin rock
can be divided into three
groups
 Igneous rocks
 Metamorphic rocks
 Sedimentary rocks
.
Engineering definition of rock
 Engineering definition of rock differ from that used
in geology
 From excavation point of vie rock is material that
cannot be excavated without blasting
 In geology, rocks are classified by how they are
formed
 All other materials would be termed as soil

9. Igneous rocks
Formation
 Formation by cooling of molted rock
materials (lava or magma)
 Magma is generated by local heating
and meting of rocks within the
earth’s crust
 Melting occurs at depths of 10-100
km
 Most composition of rock melt at
temperatures of 800-1200° C
 When magma cools it solidifies by
crystallizing into mosaic of minerals
to form ingenious rocks
 Igneous rocks can be classified as
 Extrusive igneous rocks
 Intrusive igneous rocks
 Igneous rocks are composed mainly
of silicate minerals.
Extrusive Igneous rocks (volcanic)
 Formed when magma is extruded onto
earth surface to form volcano.
 Generally finer grained and have
smoother surface
Intrusive Igneous rocks (plutonic)
 Formed when magma solidifies below
surface of earth.
 They may be exposed to the surface
when cover rock are eroded away
 Batholith are large blob-shaped
intrusions
 Dykes are smaller sheet intrusions

10. Formation
 Formation by cooling of molted
rock materials (lava or magma)
 Magma is generated by local
heating and meting of rocks
within the earth’s crust
 Melting occurs at depths of 10-
100 km
 Most composition of rock melt at
temperatures of 800-1200° C
 When magma cools it solidifies
by crystallizing into mosaic of
minerals to form ingenious rocks
 Igneous rocks can be classified as
 Extrusive igneous rocks
 Intrusive igneous rocks
 Igneous rocks are composed
mainly of silicate minerals.
Igneous rocks
 Unweather igneous rocks generally have excellent
engineering properties and good materials to build on
Intrusive rocks are especially good (slow cooling).
 Cooling process, along with various tectonic forces within
the earth produce fracturs especially in extrusive rocks
 Intact rocks between the cracks can be very strong, but
fractures form plane of weakness
 The rock can slide along these weak planes, potentially
causing instability of rock mass
 Engineering properties of weathered igneous rock are less
desirable because the rock is changing into a more soil like
materials.

11. Example of Identification of igneous rocks and types

12. Sedimentary Rocks
Formation
 Are created from sediments
 Sediments form from outer skin
of earth crusts
 Most sedimentary rocks are of
secondary origin, the contain
detrital materials derived by
breakdown of existing rocks
 Some sedimentary rocks are a
product of chemical or biological
precipitation whereas others are
organic origin.
 Since sedimentary rocks are
formed from deposits, they are
mostly bedded or stratified.

13. Sedimentary Rocks
 Soil deposits can be transformed back into rocks through the hardening process called induration or
lithification, thus forming sedimentary rocks.
 There re two types of such rocks
Clastic rocks and
Carbonate rocks

14. Sedimentary Rocks
Clastic Rocks:
• Form when deep soil deposits become hardened as a result of pressure
from overlying strata and cementation though precipitation of water-soluble
minerals such as calcium carbonate or ion oxide.
• These rocks are layered or stratified ,which makes the them
different from massive formation. The interface between these
layers are called bedding planes. Most clastic rocks are interbedded
such as conglomerates, breccia and sandstone. Those cemented
with silica or iron oxides are generally durable but may be
difficult to excavate. However, some are weakly indurated, often
only cemented only with clay and other water-soluble minerals.
These may behave much like a soil and may be much easier to
excavate.
• Fine grained and very fine-grained clastic rocks are more
common and much more problematic. Sometimes mudstone is
used to collectively described these rocks (siltstone ( derived from
silt) , claystone (derived from clay)or shale (derived from clay and well
indurated))
• These rocks have distinct bedding planes (bedding planes) and are
subjected to opening or shearing (failure) along those planes. All
except shale are easy to excavate with conventional earth
moving equipment (bulldozer).
• Some fine grained and very fine-grained elastic rocks are
subjected to slaking, which is deterioration after excavation and
exposure to atmosphere and wetting and drying cycles. Rock
which experience slaking will rapidly degenerate to soils and
thus create problem for engineering structure built on them
Slaking of clay bearing sedimentary
rocks

15. Sedimentary Rocks ( Carbonate rocks)
Carbonates Rocks:
• forms when organic material accumulate
and become indurated. Because oof their
organic origin they are called carbonates e.g.
limestone, chalk and dolomite.
• Carbonate rocks, especially limestones can
be dissolved by long exposure to water,
especially if it contains mild solution of
carbonic acid.
• Ground water often gains small quantities
of this acid through exposure to carbon
dioxide in the ground. This process often
produce karst topography which exposes may
underground very ragged rock at the
ground surface and many underground
caves and passageways.
• Sometimes rock is covered with soil, so the
surface expression of karst topography may
be hidden.
• Nevertheless, the underground caverns
remain and sometimes the ground above
caves into them This creates sinkhole.
• The caving in process may be trigged by
lowering of water table, which occurs when
well are installed for water supply purposes.

16. Example of Identification of sedimentary rocks and types

17. Metamorphic Rocks
Formation
 Derived from pre-existing
rock types and have gone
mineralogical, textural
and structural changes
 These changes are
brought by physical and
chemical environment
 Changing condition of
temperature and/ or
pressure are the primary
agent causing
metamorphic reactions in
rocks
 Metamorphic rock may
be foliated

18. Metamorphic Rocks
• Both igneous and sedimentary rocks can be subjected to intense heat and pressure within earths crust.
• These condition produces dramatic change in minerals within the rocks, thus forming metamorphic rocks.
• The metamorphic process generally improve the engineering behavior of these rocks by increasing their
hardness and strength. Nevertheless, some metamorphic rocks can still be problematic.
• Some metamorphic rocks are foliated, which means they are oriented grains similar similar to bedding planes
in sedimentary rocks. These foliations are important because the shear strength is less for shear stress acting parallel
to the foliation.
• Other metamorphic rocks are nonfoliate and have no such orientation
• Unweathered, non foliated rocks generally provide excellent support for engineering works, and is similar to
intrusive igneous rocks in their quality.
• Some foliated rocks are prone to slippahe along foliated planes
• Metamorphic rocks are also subjected to weathering, thus forming weathered rocks, residual soils and
transported soils and beginning the new geological cycle.

19. Example of Identification of metamorphic rocks and types

20. (b) MINERALS
Defination
 Naturally occurring solid elements or compound, formed by inorganic process and
has:
 Defined chemical composition
 Ordered internal arrangements of atoms
 Unique sets of physical properties
 According to the definition, oil, coal, volcanic glass (which lack order internal
structure) and manufacturing glass don’t qualify as minerals.
 Ordered internal arrangements of atoms in mineral is known as crystalline
structure (repetition of atom arrays)
 A non ordered internal arrangements is termed as amorphous or without form and
it occurs in liquids or
Formation
 When minerals solidify from liquid state or form in other ways, they yield internal
ordered solid material (crystallization).
Occurance
 Minerals comprises the soil and rock materials of the earth
 They are found in all geological environment, including alluvial sands along riverbed,
soils of plowed fields
 Despite hundreds of known minerals only 25 make up common rock forming
varieties and they influence the engineering properties of rocks and soils.

21. Mineral Identification
Identification
 Chemical properties aid in identification of some minerals but mostly physical
properties are used.
 Properties include color, streak, luster hardness specific gravity, cleavage,
fracture, crystal form, magnetism, tenacity reaction to acid.
 Color: very deceptive in limited situation, It’s the surface appearance.
 Streak: color of finely powdered mineral
 Luster: overall appearance of the surface of mineral
 Hardness: Resistance of mineral to scratching
 Specific gravity: Ratio between weight of mineral in air to weight of equivalent
volume in water ( specific gravity of minerals > 2.70)
 Cleavage : Ability to break along smooth parallel planes
 Fracture: Irregular breaks in the absence of clavage
 Crystal form: Display of well-formed crystal faces of mineral
 Tenacity: Resistance a mineral show to various destructive mechanisms such as
crushing , breaking, bending, tearing etc.
 Diaphaneity: Ability to transmit light (Transparent, Translucent, Opaque)

22. Rock forming minerals
Silicates
 Examples: Ferromagnesian, nonferromagnesians, Feldspar, quartz.
Oxide Minerals
 Iron oxides Hematite (Fe2O3) recognized as red streak and limonite(Fe2H2O) brown streak
in gravel . Magnetite (Fe3O4). Causes corrosion to reinforced concrete.
Sulfide Minerals
 Most common are pyrites (fool’s gold). It has brassy color and hardness about 3.5 to 4.
Nuisance mineral if occur in gravel. Staining on concrete may occur due to oxidation.
Carbonate Minerals
 Important carbonates are (CaCO3). It reacts with dilute Hydrochloric Acid. It has low
hardness of 3. Dissolves in water, problem of sinkhole.
Sulphate Minerals
 Include Gypsum (CaSO4.2H2O) and anhydrate (CaSO4). Soluble in water hence can cause slope
stability and failure of foundations.
Clay Minerals
 They comprise an essential portion of soil and therefore yield strong influence of soil
behavior. Examples are Kaolinite, halloysite, illite and montmorillonite. They swell in presence
of water and shrinks when dry. Causes foundation failure as a results of wetting and dry cycles.
Zeolites
 Silicate minerals related to feldspar. Na-Zeolite is obtained by adding NaCl to zeolite
material. They yield high density of negative charge and are used to soften water (removal
of Ca2+ and Mg2+)

23. Engineering Consideration of Minerals
Problems associated with various minerals may be full
appreciated by engineer bust first problematic minerals
must be if the problem is to be predicted.
1) Recognizing gypsum that lie along a proposed
tunnel centerline will provide information of
problem of swelling in presence of water and
deterioration of concrete lining.
2) Presence of pyrite in a dark shale can suggest
ultimate problem of deterioration from swelling
and acid water
3) Problem of pyrite in concrete aggregate can create
serious problem of corrosion to reinforced
concrete
4) Swelling clays in shale can problem that slope
stability may be a problem or heaving problem
Collapse of
tunnel wall
From gypsum
Slope stability
failure due to
expansive soils
Corrosion of
steel and
concrete due to
presence of
pyrite

24. (c) STRUCTURAL GEOLOGY
Structural geology
• Structural geology is the study of three-dimensional
distribution of rock formation and orientation of
weakness of plane they contain.
• Under certain conditions, these weakness plane will
control rock behavior.
• Its also involves the study of rocks that’s have been
deformed by earth stresses
Bedding planes and foliation
• All sedimentary rocks formed in horizontal or near
horizontal layers, and these layers reflects alternate
cycles of deposition.
• The shear strength along these weakness plane is
typically much less than across them, a condition called
anisotropic strength.
• When these rocks are were uplifted by tectonic forces in
the earth, the bedding planes could be rotated to a
different angle (Fig. 2.6) Because rock shear more easily
along these planes, their orientation is important.
• Many landslides have occurred on slopes with unfavorable
bedding orientation.
• Some metamorphic rocks have plane of weakness
called foliation. This characteristics is called schistosity.

25. Rock deformation under high pressure
Rock deformation
• Tectonic forces distort rock mases. In the earth crust
rocks are under high confining pressure and elevated
temperatures
• High temperature causes rock to be less brittle hence
plastic deformation
• Stress –strain relationship is as show below
• For elastic deformation (earthquake wave passes
through a rock )in plastic range, the rock returns to its
original shape.
Folds
• When horizontal compressive forces are present, the
rock distort into a wavy pattern called folds.
• Sometimes these folds are gradual, other times they
are gradual and very abrupt. When folds are oriented
concave downwards, they are called anticlines and when
they concave upwards, they are called synclines.
• Folding of rock occurs in plastic range of the curve
Compressive stresses deform the rock but upon removal of the
stress by uplift or erosion the rock retains the folded shape
• Faulting occurs when the rock raptures (fracture) as
brittle material.
On release of stress, the strain is irrecoverable i.e rock retains
the faulted shape
A-B: Elastic deformation
B-C: Plastic deformation

26. Folds in rock
• Caused by compressional stresses that buckle
the rock unit
• The trough or downward portion is called the
syncline and the crest portion is the syncline
• If only one direction of dip prevail in a fold
system, it is called monocline
• Another essential part of a fold is the axis
plane. Imaginary plane used to divide folds into
two equal parts
• The axis plane is used to describe the degree
of symmetry of the fold system
• Symmetrical
• Asymmetrical
• Overturned
Folds in Rock

27. Rock deformation under high pressure
Fractures
• Fractures are cracks in rock mass. There orientation is
very important because shear strength along these
fractures is less than the intact rock mass, so they form
potential failure planes.
• There are three types of fractures these fractures is
less than that of the intact rock; joints, shear and faults.
• Joints: Relatively minor tensile fractures that have
experienced no or minimal shear movements. They
can be as a results of cooling, tensile tectonics or
tensile stresses form lateral movement of adjacent
rocks.
• Shear: Fractures that have experienced a small shear
displacement.
• Faults: Similar to shears but have experienced much
greater shear displacement.
• Faults are classified according to their geometry and
direction of movements
• Dip-slip faults: Movement primarily along dip
• Strike-slip faults: movement primarily along stike A-B: Elastic deformation
B-C: Plastic deformation

28. Strikes and dip
Strike and Dip
• A rock mass may be unstable if it has joints oriented in certain
directions but much more stable if they are oriented in a
different direction
• For similar reasons, we are interested in the orientation of the
faults, bedding planes and other geological features.
• We express orientation using strike and dip (Fig 2.9)
• Strike of a plane is the compass direction of the intersection of
the plane and horizontal, and it is expressed as a bearing from
north. For example, f a strike in N30°W , then the intersection
of the fault plane with horizontal plane traces a line oriented at
30° west of true north. Dip also need direction. For example, a
fault with N30°W of strike may have a dip of 20°northesterly.
When expressed together, these data are called attitude and may
be expressed in a condensed form as N30°W , 20°NE .
• Attitude are usually measured in the field using Brunton campus.

29. Strikes and dip
Strike and Dip
• Sometimes we need to know the dip as it would appear in
vertical plane other than one perpendicular to the strike (Fig.
2.12).
• We may draw a cross section a cross section that is oriented
perpendicular to the slope, but at some angle other than 90°
from the strike, and we ned to know the dip angle as it appears
in the cross section. This dip is called apparent deep and may
computed as.

30. Faults in Rock
Faults
• Faults are fractures along which significant
movement has occurred
• Displacement may be measured in meter or km.
Minimum movement of 1m qualify as a fault
• Altitude of fault is described in terms of strikes
and dip
• The wall above the fault plane is called is called
the hanging wall and the portion below is the
footwall
• Movement along the fault plane can be either
 Along the dip direction (dip-slip faults)
 Along strike direction (strike slip faults)
 Combination of both strike and dip direction
(oblique faults)
Dip slip faults: Normal faults,
reverse faults or thrust faults

31. Dip slip & Strike slip faults
• Normal faults: Hanging wall
moved down relative to foot
wall.
• Reverse faults: Hanging wall
moved up relative to foot
wall.
• Thrust faults: Low deep
angle reverse faults .
Dip slip
faults
Dip –Slip faults
Strike slip faults (Wrench faults)
• Occur when relative movement is all
horizontal.
• Two types are : Right lateral strike
fault and left lateral strike fault
• Normal faults: Caused by either vertical
compressive force or horizontal
compressive force. It involves lengthening
of the earth’s crust
• Reverse faults: Caused by either horizontal
compressive force or vertical compressive
force. It involves shortening of the earth’s
crust.

32. Oblique faults
Oblique faults
• Also known as translational
fault
• Have both strike slip and dip
slip combination

33. WEATHERING
• Rocks exposed to the atmosphere are immediately subjected to physical (or mechanical ),
chemical and biological breakdown through weathering.
Physical or mechanicals weathering is the disintegration of rocks into smaller particles through physical
process and it includes;
 The erosive action of water, ice and wind
 Opening of cracks as a result of unloading due to erosion of overlying soil and rock
 Loosening through the growth of plant roots.
 Loosening through the percolation and subsequent freezing (and expansion) of water.
 Growth of minerals in cracks, which forces them to open further
 Thermal expansion and contraction from day to day and season to season
 Landslides and rock falls
 Abrasion from the downhill movement of nearby rock and soils
Chemical weathering:
• Disintegration of rock through chemical reactions between the minerals in the rock, water, and
oxygen in the atmosphere.
• Major types of reactions leading to chemical weathering include
• Solutioning, hydration, carbonation, oxidation and reduction
• For example, feldspar are susceptible to chemical weathering and weather into clay minerals
Biological weathering:
• Disintegration of rock into smaller particles caused by biological activities that produce organic
acid.

34. WEATHERING
• Rocks passes through various stages of weathering, eventually being broken doen into small
particles, the material we call soil
• These soils particles may remain in place, forming residual soil, or may be transported from their
parent rock (transported soils)
• Weathering process continues even after the rock becomes soil. As soil become older, they
change due to continued to weathering.
• The rate of change depends on
 The general climate, especially precipitation and temperature
 Physical and chemical make up of the soil
 The elevation and slope of the ground surface
 The depth of ground water table
 The presence of flora and fauna
 The presence of microorganisms
 The drainage characteristics of the soil

35. Weathering grades
• Weathering leads to general disintegration of rocks through change in mineral composition, increase in
void spaces and weakening of interparticle bonds.
• Based on visual observation, the geological society of London proposed six grades of withering as below

36. SOIL FORMATION, TRANSPORTATION AND DEPOSITION
Geologists classify soils into two major categories residual soils and transported soils.
Residual soils
• When weathering process is faster than the transport induced process included by water, wind
and gravity, much of the resulting soils remain in place.
• Its is know as residual soil, and typically retains many of the characteristics of the parent rock.
• The transition with depth from soil to weathered rock to fresh rock is typically gradual with no
distinct boundaries.
• In tropical regions, residual soils layer can be very thick, sometimes extending for hundred of
meters before reaching unweathered bedrock.
• Cooler regions and more arid regions normally have much thinner layers and no residual soil at
all.
• Example are
 Decomposed granites: sandy residual derived from weathering of granites.
 Saprolite: Not completely weathered and still retain much structure of parent rock
 Laterite: Found in tropical regions. Typically cemented with iron oxides to give it high
strength.

37. SOIL FORMATION, TRANSPORTATION AND DEPOSITION
Geologists classify soils into two major categories residual soils and transported soils.
Transported soils
• Transported soils are formed by the deposition of the sediments that have been transported from
their place of origin by various agents.
• Example are
 Glacial soils (Drift) : Transported by glacia. Can be catehorized as till, glaciofluvial soils and
glaciolacustrine soils.
 Alluvial soils (fluvial or alluvium): Transported by rivers or streams.
 Lucustrine and Marine Soils: Deposited beneath lakes.
 Aeolian soils: Deposited by winds. This mode of transportation produces poorly graded soils.
 Colluvial soils: Transported downslope by gravity..

38. Soils
Groups of soils
• In civil engineering soil is earth material that can be disintegrated by water by gentle agitation
• Soil deposit can be grouped into two main groups
 Transported soils
o Materials that’s have been moved from their place of origin
o Soil particles are segregated according to size by or during transportation process
o Process of transportation and deposition has effect on the properties of the resulting soil
o Agents of transportation can be gravity, wind, glacial, river
 Residual soils
Residual soils or sedentary soils have principally formed from weathering of rocks or accumulation of
organic materials and remain at the location of origin.
Soils Types
Depending on the grain size soil can be grouped as
 Gravel (60mm-2 mm)
 Sand(2mm-0.06 mm)
 Clay(>0.06 mm)
 Silt(>0.06 mm)
 Gravel and Sand are considered granular/ soil while Clay and Silty are considered fine grained soils
 Clay and Silt can be distinguished based of Plasticity Index