Engineering Geology Lecture 1

Course Title: Engineering Geology
Course Code: Geol. 4112
Credit hours: 3 credit or 6 ECTS
Course Category: Core course
Instructors: Azmeraw Wubalem (MSc)
alubelw@gmail.com
0935452268
Office:CNCS 3rd floor room 28

C
University of Gondar
College of Natural and Computational Sciences
Department of Geology
Engineering Geology (Geol 4112)
By: Azmeraw Wubalem
2

Course Title: Engineering Geology
Course Code: Geol 4112
Credit Hours: 3
Course Category: Core Course
Year and Semester: Year 4 Semester I
Instructors: Azmeraw Wubalem (MSc)
Email: alubelw@gmail.com
Phone: 0935452268
Office Address: CNCS building office room 28
Office free time: thuesday and Friday
Course Aim/Rationale: To increase students’ knowledge of engineering application of geology.
Learning Outcomes: After successful completion of the course, students will acquire sufficient
knowledge on the impacts of geological processes and features on engineering foundations;
students will acquire the necessary knowledge and skill to prepare engineering geological maps
for eventual use in civil engineering projects.

Course Outline
1. Formation of Soils and Engineering Use [3 hrs]
 Introduction
 Application of engineering geology
 Engineering concerns of different rocks
 Weathering processes and their effect in engineering properties of earth
materials
 Soil formation and their engineering uses

4. Subsurface Water and Engineering Works [3 hrs.]
 Definitions, terminologies, zones, occurrences
 Properties of sub surface rocks (storage and
transmissivity of rocks)
 Dewatering excavation for foundations,
drainage by electro-osmosis, engineering sub
drainage
 Water quality and engineering structures
5. Dams and Dam Sites; Earth Works; Reservoir
Engineering Geology [6 hrs.]
 Classification of dams (gravity, buttress,
arch), spillways, outlet and penstock
 Problems related with dam
 Channel section problems
 Embankment dams classification and
geological consideration in design
 Geology impacts on dam reservoir and
spillway design
2. Engineering Site Investigation and Exploration [6 hrs.]
 Site investigation (stages, tools, methods)
 Disturbed and undisturbed samples (samples and
samplers)
 Contents of borehole log, logs of soil materials, logs
of core boring, electrical logging, resistivity logging,
magnetic and gravity measurement
3. Hazardous Earth Processes and Engineering Works [4
hrs.]
 Landslides and other displacements
 Earthquakes and its impact on engineering structures
 Volcanic hazards
 Ground subsidence, ground fissure and Expansive
soils and their impact on engineering structures

6. Engineering Geology of Tunnels [6 hrs.]
 Types of tunnels and different site investigation for tunneling
 Tunnel drilling methods in different geological conditions
 Geological condition and tunnels, tunnel support analyses
7. Engineering Geology and Shallow Foundation Structures [4 hrs.]
 Engineering geology of bridges
 Engineering geology and building foundation
 Engineering geology and pavements
8. Engineering Geology, River Engineering and Hydraulic Structures [4 hrs.]
 Weirs and river diversions
 Dykes, breakwaters and tailing dams
 Cut of trenches
 Critical compaction, seepage and uplift pressures vs hydraulic structures
 Geologic factors in the design and construction of weirs and river diversions.

Course Assessment : Quiz = 10%,
Assignment = 10%, Presentation = 15%, Test
1 = 15%, Test 2 = 15% and final exam 50%
Course policy
Students:
Ø Should attend 85% of class to sit final
exam.
Ø Should submit all assignments/home
works on due time.
Ø Should actively participate in
assignments work, lectures class,
tutorial class, group discussion and
project works
9. Construction Materials [2 hrs.]
 Construction materials in
engineering
 Mining methods
 Test of construction materials
10. Engineering Geological Mapping
[3 hrs.]
 Maps, features and attributes of
engineering geological maps
 Methods and tools used in
production of engineering
geological maps and cross
sections

Recommended References
1. David George Price (2009) Engineering Geology Principles and Practice
2. Bell F.G. (2007), Engineering Geology, pub Elsevier.
3. Steve Hencher (2012) Practical Engineering Geology
4. Manual on Subsurface Investigations (2019)
5. Bell F.G (1999) Geological hazards
6. Neil Anderson et al. (2008) Geophysical Methods Commonly Employed for Geotechnical Site
Characterization
7. WP (2011) Guidelines for landslide susceptibility, hazard and risk assessment and zoning
8. Blyth F.G.H & Freitas D.H. (2007), A Geology for engineers, pub Elsevier, Delhi, India.
9. Deerman W. R (1991), Engineering geological mapping. Oxford, Pp. 1-23.
10. Franklin J.A. and Dusseault M. (1991) Rock Engineering Applications), McGraw Hill, New York, 431p.
11. Garg S.K. (2008), physical and engineering geology, Khanna pub, Delhi, India, pp. 30-
1. 257.
12. Goodman, R.E. (1989) Introduction to Rock Mechanics, 2nd Edition, John Wiley & sons.
13. Hoek E. & Bray J.W. (1991) Rock slope engineering.
14. Johnson R.B and DeGraff J.V. (1988) Principles of Engineering Geology, Wiley, New York, London,
497p.

Chapter 1 Outline
9
• Definition of Engineering Geology
• History of Engineering Geology
• What do Engineering Geologist do?
• What an Engineering Geologist needs to know?
• The role of Engineering Geologist
• Functions of Engineering Geology
• Engineering concerns of different rocks
• Weathering processes and their effect in engineering properties of
earth materials

Q1. Which Dam site is appropriate? Why?
A B
JointsJoints
Reservoir
Reservoir
A. It is appropriate because the
orientation of the discontinuity is
opposite to the flow direction of the
water
B. It is not appropriate because the orientation of
the discontinuity is parallel to the flow direction of
the water that may pose serious seepage and
leakage. It will also be resulted in overturning

Q2.Where is the appropriate foundation? Why?
A?
B? C?

Q3. Which discontinuity orientation will pose hazard? Why?

Q4. Which discontinuity orientation will pose hazard? Why?

Q5. Is this the Original Earth’s surfaces?
14

tower of pisa, italy
Q6. What is happening for the building? What is the problem and its causes? What will be the solution?

road damage due to shrinkage of subsoil
Q7. What is the problem and its causes? What will be the solution?
road constructed on slope wash material
with unproper protection
effect of flood
effect of flood
Loose Soil

Introduction
What is Engineering Geology?
• Is an applied discipline of Geology that relies heavily on geologic principles and processes in the
application of geologic fundamentals to engineering practice.
• Is a science devoted to the investigation, study and find a solution of the engineering and
environmental problems that arise as the result of the interaction between geology and human
activities (IAEG).
• IAEG define Eng’ Geology as the study of earth materials and its interaction with geological env’t
& engineering practice.
• It provides basic geological data for the safe construction and remediation of engineering structures.
• IAEG-International Association of Engineering Geologist

Cont.…
• As its name implies, it is an interdisciplinary profession in which the engineering geologist works
closely with, must understand and respond to the needs of the engineer/designer of the project.
To do so, one must be proficient with the properties and uses of earth materials outside those
commonly encountered by other geologist.
In this case, the function or task of an engineering geologist is to take back the geologic
fundamentals and to look forward the engineering meaning.
Engineering Geologist provides a systematic knowledge of construction material, (its occurrence,
composition, durability and other properties).
The knowledge of the geological work of natural agencies such as water, wind, ice and
earthquakes helps in planning and carrying out major civil engineering works.

Cont.…
The knowledge about quantity and depth of groundwater is required in connection with water
supply, irrigation, excavation and many other engineering works above it.
The foundation problems of dams, bridges and buildings are directly related to the geology of the
area where they are to be built.
In tunneling, constructing roads, canals, and in determining the stability of cuts and slopes, the
knowledge about the nature and structure of rocks is very crucial.
The stability of the engineering structures is increased if the geological features like faults,
joints, bedding planes, folding and solution channels in the rock beds are properly located and
suitable treatments are carried out & vice versa.
For these all projects, a detailed geological report that is accompanied by geological maps and
cross sections are helps in planning and constructing the project work.

Cont.….
The cost of engineering works will considerably be reduced if the geological survey of
the area concerned is done before hand carefully.
Who is responsible for these failure?
Failure due to d/t
factors mostly
absence of proper
investigation of
earth materials

History of Engineering Geology
• The first book entitled Engineering Geology was published in 1880 by William
Penning.
• The first American engineering geology text book was written in 1914 by Ries
and Watson.
• The need for geologist on engineering works gained world wide
attention in 1928 with the failure of the St. Francis dam in California and the loss
of 426 lives.
• More engineering failures which occurred also prompted the requirement
for engineering geologists to work on large engineering projects. 21

What do Engineering Geologist do?
• In consulting (designing) or contracting (construction) companies with a team of engineers,
some of whom will be specialized in the ﬁeld of geotechnical engineering, which concerns
the interface of structures with the ground.
• In site investigation about the geological conditions at a site and to present these in a
simpliﬁed ground model or series of models.
• Geological and Engineering Geological Models should contain and characterize all the
important elements of a site.
• Primary geological soil and rock units are usually further subdivided on the basis of factors
such as degree of consolidation, strength, fracture spacing and style, hydrogeological
conditions or some combinations
• Models must identify and account for all the natural hazards that might impact the site
22

• c
23
What do Engineering Geologist do?

What an Engineering Geologist needs to know?
• Firstly, he needs to be fully familiar with geology to the level of a
traditional Earth Sciences degree.
• He should be able to identify soil and rocks by visual examination
and to interpret the geological history and structure of a site.
• He also needs to have knowledge of geomorphological processes,
and be able to interpret terrain features and hydrogeological
conditions.
24

• Methods and techniques for surface and sub-surface investigation.
• Properties of soil and rock, such as strength, permeability and deformability
• How to measure these in the laboratory (material scale)and in the ﬁeld and how
to apply these at the large scale (mega scale) to geological models.
• Methods for soil and rock description and classiﬁcation for engineering
purposes.
• Weathering processes and the nature of weathered rocks.
• Quaternary history, deposits and sea level changes.
• Nature, origins and physical properties of discontinuities
25

• Hydrogeology: inﬁltration of water, hydraulic conductivity and controlling
factors.
• Water pressure in the ground, drainage techniques.
• Key factors that will affect engineering projects, such as forces and stresses,
earthquakes, blast vibrations, chemical reactions and deterioration.
• Numerical characterization, modelling and analysis.
26

What are the areas that will be covered by Engineering Geologist?
 Geological Hazard Mapping/ assessment and mitigation
 Geotechnical site investigation
 Construction material study, evaluation and mapping
 Soil Erosion/land degradation assessment and managements
 Land use mapping and management
 Water supply and irrigation
 Assessments of rock mass stability for mining activity
27

The Main Roles of Engineering Geologists are:
Description of the geologic environment pertinent to the engineering practice.
Description of earth materials, their distribution, and general physical and
chemical characteristics.
Deduction of the history of relevant events affecting the earth materials
Forecasting of future events and conditions that may develop in a given site.
Recommendation of materials for representative sampling and testing.
Recommendation of ways to handle and treat various earth materials and
processes (stabilizing or making suitable).
Recommending or providing criteria for excavation design, particularly slope
geometry to stabilize.
Inspection during construction activities to confirm conditions/ requirements.
Etc…….

The Role of Engineering Geologist
29

31
1.2 Scope of
Engineering
Geology: link
with other
disciplines
Abdullah
Sabtan (2010)

Applications of Engineering Geology:
 Civil engineering:
 Buildings, industrial and offshore foundations.
 Reservoirs, fills and embankments.
 Slopes.
 Roads, airports and industrial pavements.
 Bridges.
 Retaining structures.
 Tunnels and underground space facilities.
 Mining and resource development.
 Environment: waste containment systems and site remediation.
 Military engineering: recent developments.
 Groundwater resources development and management.

Significance of Engineering Geology
 To recognise potential problematic ground
conditions prior to detailed design and construction.
 To identify areas susceptible to failure due to
geological hazards
 To establish design specifications/ standards
 To have best selection of site and construction
materials for engineering purposes.
 To locate groundwater appropriately.
 To define properties of geological structures and
earth’s materials.

 Engineering Geology is prominent for civil engineering to provide information
in three most important areas:
Resources for construction:- dimension and building stone, aggregates and
fills
Finding stable foundations:- Present is the key to the past –Geology; and
Past is the key to the future – Engineering
Mitigation of geological hazards:- Identify problems, evaluate the costs,
provide information to mitigate the problem 34
Importance of Engineering Geology in DevelopmentSignificance of Engineering Geology

 Engineering Geologists: investigate the engineering properties of rock, sediment and soil
below man-made structures such as roads, bridges, high-rise buildings, dams, airports, etc.
Compiled by Samuel Abraham 35

Cont.…
 Generally Engineering geology is the application of geological knowledge in
design, construction and performance of engineering works; by studying:
Soil mechanics
Rock mechanics
Ground water effects
on engineering works
Effects of geological
structures
Slope materials
Etc…

Why Study Engineering Geology ? because
 All engineering works are built in,
with or on the ground.
 The ground will always react to the
construction of the engineering
works.
 The reaction of the ground
(engineering behaviour) to the
engineering work must be
accommodated (within allowable
limit) to be stable.

cont’d
To arrive at the engineering behaviour of the ground, there are
common relations or equations between rock, rock mass and
engineering/structure:
1. Material properties + mass fabric = Mass property
2. Mass property + environment = Engineering geological
condition
3. Engineering geological condition+ changes produced by
engineering work = Engineering Behaviour of the
Ground.
Let’s see all the variables in the equations above and their
significance:
• Material: rock, soil, and fluids and/or gas
• Material property: density, shear strength, deformability,
etc.
38

Cont.
• Mass fabric: beds, dykes, veins, joints, faults, etc.
• Mass: ground mass, volume of ground which will be
influenced by or will influence the engineering work.
• Environment: includes
– climate,
– stress condition,
– Natural and man-made hazards and earthquakes, etc.
– Time: immediate after construction, after construction
and through its life time.
In the three equations all the factors leading up to the
description of the engineering geological situation/
condition may be established by the process of site
investigation (chapter two).
39

Formation of Rock, Soil & Engineering use
Minerals, rocks and soils
• The activities of the Engineering Geologist are directly or indirectly associated
with soil, rocks and rock-forming minerals.
• Thus the knowledge of these materials useful in making estimates of site
conditions and in formulating site investigation programs for engineering
purpose,
Mineral; -Minerals are solid, naturally occurring, inorganic, well defined
structures, have a fixed composition and are made of one or more elements.

Rock
• Rock is defined geologically as a naturally occurring consolidated material
composed of one or more minerals aggregate.
• A map-able rock unit to the geologist, may be a soil to the civil engineer or
engineering geologist.
• Highly weathered basaltic or any other rock type would appear as rock (basalt)
on a geologic map but would have the physical properties of an engineering
soil.
• A commonly used engineering definition of rock is that of a hard, compact,
naturally occurring aggregate of minerals.
• The bases for the engineering definition of rock are:
The physical state and the mechanical behaviour of the material which are
important to the engineer.

Cont.…
For most engineering geological applications:
• Physical properties that characterize three major rock groups and their common rock
types are important rather than to use detailed mineralogical and/or petrographic
analyses and the specialized rock names. Except clay minerals.
• The mass properties (with discontinuity) of the rock also have engineering importance
than individual or intact rock sample. This is because all rocks are discontinuous as a
result of partings such as joints, bedding, foliation and faults, etc.
• The properties/ characteristics of discontinuities should also be well studied for the
use of the rocks.

Rock types
Geological classification which based on its origin and mode of formation/
genetic
- Igneous
- Sedimentary
- Metamorphic
 Each genetic class represents different engineering properties, that affected by
the structures, textures of rocks type and processes involved in the formation of
rocks.
For engineering purpose rocks are classified into;
Intact rock- rock without discontinuity
Rock mass- with discontinuity (also classified into different by many
scholars, eg RMR, RQD and Q-system of classification)

MAGMA
IGNEOUS
Plutonic
Solidification

MAGMA
Volcanic
IGNEOUS
Plutonic
Solidification

MAGMA
Volcanic
IGNEOUS
Plutonic
Uplift
Solidification
Weathering &
Erosion

MAGMA
Volcanic
IGNEOUS
Plutonic
SEDIMENT
Solidification
Weathering &
Erosion
SEDIMENT

MAGMA
Volcanic
IGNEOUS
Plutonic
SEDIMENT
SEDIMENTARY
Solidification
Weathering &
Erosion
Erosion
Transport
Deposition

MAGMA
Volcanic
IGNEOUS
Plutonic
SEDIMENT
SEDIMENTARY
Solidification
Weathering &
Erosion
Deposition
Burial/Compaction
Cementation

MAGMA
Volcanic
IGNEOUS
Plutonic
SEDIMENT
SEDIMENTARY
METAMORPHIC
Increased P&T
Solidification
Weathering &
Erosion
Deposition
Burial/Compaction
Cementation

MAGMA
Volcanic
IGNEOUS
Plutonic
SEDIMENT
SEDIMENTARY
METAMORPHIC
Increased P&T
Melting
Solidification
Weathering &
Erosion
Deposition
Burial/Compaction
CementationCan you see
any shortcuts?

MAGMA
Volcanic
IGNEOUS
Plutonic
SEDIMENT
SEDIMENTARY
METAMORPHIC
Increased P&T
Melting
Solidification
Weathering &
Erosion
Deposition
Burial/Compaction
Cementation

Relationships between main rock groups and their engineering properties/
characteristics
• For an intact specimens of rocks, their engineering properties are uniquely
related to the rock type (especially to igneous and metamorphic rocks).
• In igneous and metamorphic rocks mineralogy, texture, crystal (grain) size
and structure are factors affecting their engineering properties.
• In sedimentary rocks due to:
– Complex interaction of sedimentary environment / Parent material
– The detrital and/or soluble products of weathering
– Transporting mechanism
– Lithification and
– Post depositional changes, the engineering properties can be affected;
Special care should be taken in interpreting sedimentary rocks for engineering
geological applications. So it requires a classification system that can account
for all factors involved

For Examples
Igneous rocks
• Igneous rocks are mostly composed of silicate minerals and interlocking textures (except
pyroclastic).
• For fresh igneous rock, mineralogy and texture are responsible to provide high strength and
excellent elastic deformation characteristics. Crystal size inversely affects strength.
• Engineering geologic classification of igneous rocks is based primarily on composition of
crystal (grain) size.
Sedimentary rocks
• Sedimentary rocks present many challenges to the engineering geologist.
• Sedimentary rocks originated by transport and deposition of clastic sediments (clay to gravel)
and chemical sediments by crystallization from a solution (limestone, salt, gypsum).
• Primary sedimentary structures creates discontinuities in addition to secondary structures like
joints and faults that highly affect the engineering properties
• These primary and secondary structures reduces rock strength or rock quality.

Metamorphic rocks
• Metamorphism causes textural, structural and mineralogical changes in the original rocks
which results in the modification of its physical properties. The metamorphism may improve
the strength of the rock.
• Metamorphic rock classification is based primarily on the presence or absence of foliation.
• Massive (non foliated) quartzite and marble formed from pure sandstone and pure limestone
respectively are characterize by high strength because of textural change (absence of
foliation).
• Slates, phyllites, schists, and gneisses by comparison progressively exhibit mineral
reorientation and generation of crystalline textures from clay-rich clastic sedimentary rocks.
For Examples

Rock Properties for Engineering
Rocks are significant for two major reasons in engineering:
1. As building materials for constructions
2. As foundations on which the constructions are setting
For the consideration of rocks as construction and foundation, geological
engineers concern about the rock’s density, strength, compressibility,
durability, workability, and stability
58

Engineering concerns of different rocks
The three types of rocks;
a. Igneous
b. Sedimentary
c. Metamorphic;
Point out some engg’ problems of rocks???
59

Engineering Considerations of Igneous Rocks for aggregates
1. Silica rich fine-grained igneous rocks cannot be used as aggregates in Portland
cement due to volume expansion caused by the Alkali-silica reaction. This can
be controlled by:
Can be used in low alkali cement
Non-reactive aggregates go with the high alkali cement
Add pozzolans, coal-ashes, etc. in the aggregate-cement mixture to
minimize the reaction.
2. Coarse-grained igneous rocks (e.g., granite, syenite, etc.) are not used for
aggregates for constructions because their low abrasion resistance; but fine-
grained igneous rocks (e.g., basalt) are good for aggregates (e.g., basalt as
paving aggregates goes with asphalt.)
3. Sitting of foundations needs to avoid weathered rocks (e.g., dams, bridge
piers, etc.) 60

Cont’d
4. Igneous rocks are good for dimension stone, if they are resistant to weathering but
need to avoid fractures.
5. Massive intrusive bodies such as stocks and batholiths tend to have relatively
homogeneous compositions and textures that are three-dimensional throughout.
6. Tabular intrusive bodies such as dykes and sills may create more construction or
rock-utilization problems than massive intrusive because of equi-dimensional
crystals that is found in massive intrusive
7. All things considered, tabular intrusive create more problems in mapping and in
engineering construction and rock use than the massive intrusive.
8. Crystal size of igneous rocks inversely affects strength. 61

Engineering Considerations of Sedimentary Rocks for aggregates
1. The sedimentary rocks also have the Alkali-silica reaction problem when used as
aggregates with Portland cement. The sedimentary rocks with this problem are chert
& greywacke
2. Fine-grained sedimentary rocks like limestone and dolomite are the best for
aggregates while siltstone, shale, conglomerate, and quartz sandstone are not
acceptable
3. Stream and terrace gravel contains weak pieces, they are not good for aggregates in
concrete. Weathered chert, shale, and siltstone can cause pop-outs at the concrete
surface after freeze-thaw cycles;
4. Coarse-grained limestone is not good for aggregates 62

Cont’d
5. Any Civil Engineering structures to be constructed on carbonate rocks needs a
very careful study as they can have sinkholes, karstic features and different
solution structures
6. When conglomerates are found in dam abutments & foundation, they need
special treatment to increase their strength and reduce permeability.
7. Sedimentary rocks containing anhydrite/ gypsum are troublesome to
Engineering Structures such as dams, high ways, tunnels etc.
8. Primary & secondary structures reduce rock-mass strength and may contribute
to slope instability.
63

Engineering Considerations of Metamorphic Rocks for aggregates
1. The modifications may improve some engineering properties, whereas other changes
may result in reductions in strength, slope stability, and abrasion resistance.
2. The metamorphic rocks also have the Alkali-silica reaction problem when used as
aggregates with Portland cement. The metamorphic rocks with this problem are
argillite, phyllite, impure quartzite, and granite gneiss
3. Coarse-grained gneiss can be abraded severely when used as aggregates;
4. The stability of rock mass in metamorphic rocks greatly affected by the foliation
orientation;
5. The stability of rock slopes is affected by the attitude of foliation with respect to rock
slope direction.
64

Cont’d
6. Marble can be subjected to the same problems like limestone e.g., leakage of
reservoirs, sinkhole collapse, solution cavities, and channels.
65

Geomorphological Process Acting on the Earth Surface
 Physical processes which create and modify landforms
on the surface of the earth
 Endogenous (Endogenic) vs Exogenous (Exogenic)
Processes
A. Endogenous Processes (internal)
Are large-scale landform building and transforming
processes
– they create new relief.
1. Igneous Processes
a. Volcanism: Volcanic eruptions 
Volcanoes
b. Plutonism: Igneous intrusions
2. Tectonic Processes (Also called
Diastrophism)
a. Folding: anticlines, synclines, mountains
b. Faulting: rift valleys, graben, escarpments
c. Lateral Faulting: strike-slip faults
d. Earthquakes evidence of present-day
tectonic activity

B. Exogenous Processes
• Also called Gradational Processes, they comprise degradation
and aggradation
– they modify existing relief.
• A continuum of processes (– Weathering  Mass Wasting 
Erosion  Transportation Deposition)
• These processes are carried through by Geomorphic Agents:
gravity, flowing water (rivers), moving ice (glaciers), waves and
tides (oceans and lakes), wind, plants, organisms, animals and
humans
1. Degradation Processes  Also called Denudation
Processes which involves; Weathering, Mass Wasting,
Erosion and Transportation
2. Aggradation Processes
a. Deposition – fluvial, eolian, glacial, coastal, alluvium.

Weathering – the physical & chemical breakdown of rocks.
Atmosphere (gas)
Lithosphere (solid)
Hydrosphere (liq.)
Involving an interaction
between the 3 spheres
of the earth.
Weathering

Cont’d
The susceptibility of rock to weathering depends on the:
– Mineralogical content
– Permeability
– Cohesion
– Fracture spacing – which is determined essentially by genesis and history of
rock.
71
Bowen's Reaction Series- IMPORTANT!
Olivine
(Na-feldspar)Biotite
Quartz
Pyroxene
Amphibole
Muscovite
Plagioclase
(Ca-feldspar)
Orthoclase
Basalt
Rhyolite

Cont’d
72
Bowen's Reaction Series- IMPORTANT!
Olivine
(Na-feldspar)Biotite
Quartz
Pyroxene
Amphibole
Muscovite
Plagioclase
(Ca-feldspar)
Orthoclase
Basalt
Rhyolite

Factors affecting weathering
Factors Rate of weathering
Slow Fast
1. Properties of parent rock
a. Mineral Solubility Low High
b. Rock structure Massive Fractured
2. Climate
a. rain fall Low Heavy
b. temperature Cold Hot
3. Presence or absence of soil
a. thickness of soil None Thick soil
b. Organic activities Sparse Abundant
4. Length of time Short Long
5. Temperature at which the minerals
originally formed (zone of stability)
Low temp. High temp.

Types of Weathering
• Physical:
1. Freeze/thaw
2. Exfoliation
3. Abrasion
4. Salt wedging
• Chemical (biogeochemical):
1. Hydrolysis: minerals react with H2O
H+ replace soluble parts; OH- combine with
mineral cations
2. Hydration: mineral combines with H2O
3. Oxidation: mineral combines with O2 (lose
electron)
Reduction: loss of O2 (gain electron)
4. Carbonation: oxides combine with acids to make
carbonates
5. Complexation: organic acids form organic
complexes with metal cations
mechanical weathering:
1. Freeze/thaw
2. Exfoliation
3. Abrasion(water, ice, wind)
4. Salt wedging
Chemical weathering
1. Hydrolysis: minerals react with H2O
(H+ replace soluble parts; OH-
combine with mineral cations)
2. Hydration: mineral combines with
H2O
3. Oxidation: mineral combines with
O2 (lose electron) Reduction: loss of
O2 (gain electron)
4. Carbonation: oxides combine with
acids to make carbonates
5. Complexation: organic acids form
organic complexes with metal
cations

Cont..
Freeze
Abrasion(water) Salt wedging (krast formation)
Exfoliation

Weathering Effects
• Weathering effects generally decrease with depth, although zones of differential weathering
can occur and may modify a simple layered sequence of weathering at different depths.
• Examples:
– Differential weathering within a single rock unit, apparently due to relatively higher permeability
along fractures.
– Differential weathering of contact zones associated with thermal effects such as interflow zones
within volcanic.
– Differential weathering due to compositional or textural differences
– Differential weathering along permeable joints, faults, shears, or contacts which act as conduits
along which weathering agents penetrate more deeply into the rock mass; and
– Topographic effects, etc.
77

The Significance of Weathering to Engineering
Weathering does not correlate directly with specific geotechnical properties used for many rock
mass classifications.
However, weathering is important because it may be the primary criterion for determining:
– Depth of excavation
– Cut slope design
– Method and ease of excavation, &
– Use of excavation materials
Major engineering parameters influenced by weathering:
– Porosity,
– Absorption,
– Compressibility,
– Shear & compressive strength,
– Density, and
– Resistance to erosion 78

How can you identified weathered rocks?
Weathering is indicated by changes in:
– The colour and texture of the body of the rock,
– Colour and condition of fracture fillings and surfaces,
– Grain boundary conditions, and
– Physical properties such as hardness.
79

Definition of soil ( depends on discipline; Geology, Soil science, Engineering.)
I. To a geologist: unconsolidated material formed in situ/transported and deposited in
original or in new place –either bedrock or sediment.
• Profile from alteration of parent material.
• A source of clastic sediment/organic material
• Residual vs. “transported” soils
II. To a soil scientist: organic-rich material that supports plant growth.
– based mostly on agricultural importance and life support.
– important considerations: fertility, texture, drainage
III. To an engineer: any unconsolidated material above bedrock and can be easily excavated
without blasting/ any explosive method/
- important considerations:
• thickness
• strength /bearing capacity/
• water conditions
Soil Formation

Soil Formation
• Soil forms when weathered parent material interacts with environment.
• i.e. Soils are formed by weathering of rocks due to mechanical disintegration
or chemical decomposition.
• Physical (Mechanical): disintegration of parent materials into small piece;
increases surface area:
– surface area increases by same factor as particle size decreases
• Chemical (Biogeochemical) : primary minerals are broken down and secondary
minerals are formed. (undergone chemical changes)

Soil formation is largely a function of five factors:
1.The parent material (rock) on which the soil develops,
2.Climate
3.Local topography
4.Organisms (plant and animal life),
5.Time (age of the rock or parent material)
Parent materials
 The type of rock in an area affects soil formation. Some rocks do not weather
as rapidly as other do.
 Rocks that do not break down easily do not form soil rapidly.
 For example; In some climates it takes along time for granite to break down. So
soil formation from granite is slow. But sandstone breaks easily and forms soil
quickly. The structures, mineral arrangement, texture and grain size also affect
the rate of weathering.

Climate
• Soil climate has two major components; moisture (precipitation/ rainfall) and temperature,
influencing evaporation.
• In areas with heavy rainfall and warm temperatures, weathering takes place more rapidly.
• Heavy rainfall may wash much of the topsoil away. Since Organisms are more plentiful in these
areas, the soil is quickly replaced.
• They speed up the chemical and mechanical weathering of rocks.
Time
• Time is one of the most important factors in soil formation.
• The longer a rock is exposed to the forces of weathering, the more it is broken down. Mature soil
is formed if all three layers have had time to develop
Topography (relief or surface feature)
• The surface features of the region also determine the speed at which soil is formed. On very steep
slopes, rainwater running off the land erodes the soil and exposes rock to weathering
Soil formation is largely a function of five factors:

Engineering use of Soils
1. As building materials for constructions
2. As foundations on which the constructions are setting
Examples of physical Weathering: no change in chemical composition--just
disintegration into smaller pieces

Your job as an Engineering Geologist!!
Recognize problems.
Propose an engineering solutions.
There are many engineering solutions to any geological/ constructional
problem.
If you do not recognize the geological problems the engineering construction can
be at great risk
Hence, be an engineer of site investigator !!!

86
(d) Relevance of Engineering Geology in Ethiopia:
 Dams and Reservoirs: for Hydropower, Irrigation,
Drinking, etc
 Railways,
 Roads,
 High rise buildings,
 Mining,
 Waste disposals and environmental issues,
 Energy development: Geothermal, Wind, etc.
 Geological Construction Materials

Engineering Geological Software
1. GIS and ERDAS/Envi
2. Global Mapper and Google Earth
3. Sentinel SNAP
4. Excel
5. GeoStudio
6. Rocscience
7. GeoSystem
8. PLAXIS
9. Stereonet etc
10. Strater
11. Earthwork
12. IP2WIN etc.

88
1.3 Sources of Information in Engineering Geology
 Existing data/previous studies: data, maps, reports, publications, etc.
 Use of satellite imagery and remote sensing information
 Field investigations: indirect methods (geophysics) and direct methods.
 Laboratory Tests

Lecture 1Provide
solutions, not
problems
Come early,
stay late
you need to
learn to only
have fun
after all of
your work is
done
I Will work
Hard ,I Will
Succeed

36
C
End of chapter
•This is all what I have to say.
•Thank you too much for your eyeful
attention!

Engineering Geology Lecture 1

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Engineering Geology Lecture 1