Introduction to Engineering Geology S6.pdf

Red Sea University
Faculty of Earth Sciences
General Geology Department
Semester Six
Abazar M. A. Daoud, MSc in Applied and Engineering Geology

Course Description & Contents
.
1) Definition of Engineering Geology
2) Rock Mechanics.
3) Soil Mechanics.
4) Seminars Related to Engineering Geology

Useful References
1) Principles of Geotechnical Engineering, Das M. Braja, (2010).
2) Foundations on rocks, Duncan C. Wyllie, (2005).
3) Engineering Geology, Bell, F., Second Edition (2007).
4) Practical Rock Engineering, Evert Hoek.
5) Engineering rock Mechanics an introduction to the principles
(4thEdi.), Hudson, J. A., and Harrison, J. P. (2005).
6) Geotechnical Engineering Investigation Handbook (2ndEdi.),
Taylor & Francis Group (Pub.), Hunt, R. E. (2005).
7) Engineering Geology, Charles, E. Merrill Co. (Pub.), Mathewson,
C. C. (1981).

Definition of Engineering Geology
➢ Geology can be defined as the scientific study of the Earth and
especially the rocks and soils that make up the Earth: their origins,
nature and distribution, and the processes involved in their formation.
➢What is Engineering Geology?
o Engineering geology is the application of geological data, techniques
and principles to the study of rock and soil surficial materials, and
ground water. This is essential for the proper location, planning,
design, construction, operation and maintenance of engineering
structures. Engineering geology complements environmental geology.

o Engineering geology then engineering projects such as the design of a
bridge, construction of a dam or preventing a landslide. may be defined as
the scientific study of geology as it relates to civil
Engineering geologists need to identify the local rock and soil conditions at a
site and anticipate natural hazards such as earthquakes so that structures can
be designed, constructed and operated safely and economically.
He (or she, throughout) needs to work with civil engineers and understand
what they are trying to do and the constraints under which they work. His
remit and responsibilities can be extensive, covering all of the Earth Sciences,
including geophysics, geochemistry and geomorphology.
➢What does Engineering Geology study?
Rock, soil, water, the interaction among these three constituents, as well as
with engineering materials and structures.

➢What an engineering geologist needs to know???
It is difficult to define engineering geology as a separate discipline but
easier to define the subject areas with which an engineering geologist
needs to be familiar. These include:
1. GEOLOGY
➢An in-depth knowledge of geology: the nature, formation and
structure of soils and rocks. The ability to interpret the geological
history of a site.
2. ENGINEERING GEOLOGY AND HYDROGEOLOGY
3. GEOMORPHOLOGY
4. CIVIL ENGINEERING DESIGN AND PRACTICE
5. SOILAND ROCK MECHANICS

➢Engineering Geologist must be know:
1-Rock and Soil descriptions and identifications;
2-Engineering properties of rocks and soils (e.g., foundation), materials for
construction (e.g., aggregates);
3-Rock weathering and soil development;
4-Map reading, both topographic and geologic;
5-Structure aspects –bedding, joints, and faults;
6-Mass movement and landslides;
7-Running water-erosion, and flood effects;
8-Groundwater control during construction, water supply, pollution, subsidence, and
slope instability;
9-Shoreline erosion and protection;
10-Earthquakes and earthquake engineering;
11-Subsurface geology, and condition of stress at depth (for excavation, tunnelling,
etc.)

Engineering Geology Close to Life
➢ Some recent nightmare memories in Sudan and other world
countries

Rock Mechanics
➢What is Rock Mechanics?
Rock mechanics is a science that uses the principles of mechanics to describe
the behaviour of rock for engineering purposes.
➢Rock Definitions
➢The Geological Definition of Rocks
Material of the Earth’s crust, composed of one or more minerals strongly
bonded together that are so little altered by weathering that the fabric and the
majority of the parent minerals are still present.
➢The Engineering Definition of Rocks
Rock is the hard and durable material that cannot be excavated without
blasting. Or The earth materials that do not slake when soaked into water.
Rock
Mechanics
Rock
Mechanics

➢ Engineering Considerations of Igneous Rocks
(1) Fine-grained of alkali igneous rocks cannot be used as aggregates in
Portland cement due to volume expansion caused by the Alkali-silica
reaction.
(2) Coarse-grained igneous rocks (e.g., granite, syenite, etc.) cannot be
used as aggregates in constructions because its 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) Siting of foundations needs to avoid weathered rocks (e.g., dams,
bridge piers, etc.).
(4) Igneous rocks are good for dimension stone (tombstone etc.) because
their resistance to weathering but need avoid fractures.

➢ Engineering Considerations of Sedimentary Rocks
(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 greywacke.
(2) Fine-grained sedimentary rocks like limestone and dolomite are the
best for being used as aggregates; 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.
(4) Coarse-grained limestone is not good for aggregates;
(5) Sinkhole problem in carbonate terrains due to the high dissolvability
of limestone and dolomite.

➢ Engineering Considerations of Metamorphic Rocks
(1) The metamorphic rocks also have the Alkali-silica reaction problem
when used as aggregates with Portland cement. The metamorphic rocks
with this problem are phyllite, impure quartzite, and granite gneiss.
(2) Coarse-grained gneiss can be abraded severely when used as
aggregates.
(3) For metamorphic rocks the stability of rock mass greatly affected by
the foliation orientation.
(4) Marble as a metamorphic rock from carbonate sedimentary rocks
can cause similar problems, eg., leakage of reservoirs, sinkhole collapse,
solution cavities, and channels.

Rock Substances or Rock Materials refers to a block or fragment of
rock free of defects (discontinuities), in which its hydraulic and
mechanical properties are controlled by the petrographic characteristics
of the material, whether in the fresh or decomposed state. Classification
is based on its uniaxial compressive strength and hardness.
Or It refers to the consolidated and cemented assemblage of mineral
particles form the intact blocks between discontinuities in the rock mass.

➢ In situ rock (Rock Mass) refers to the rock mass that normally
contains defects (discontinuities), which separate the mass into blocks
of intact rock and control the hydraulic and mechanical properties.
Classification is based on rock quality, with the mass generally termed
as competent or incompetent.
Types of discontinuities: faults, dykes, joints, fractures, cavities,
bedding planes, cleavage planes, and foliation planes.
➢ Rocks are significant for two major reasons in engineering:
(1) As building materials for constructions;
(2) As foundations on which the constructions are setting.

2/ Engineering properties of rock mass according to ISRM ( Brown,
1981)
1-Field observations (discontinuities description)
2-Mechanical Properties (intact rock)
3-Core logging
❖Question:
What differences between Intact Rock and Rock Mass???

1/ Field observations (discontinuities description)
The rock mass is described by the following items according to ISRM
(Brown, 1981):
1. Colour.
2. Weathering: (Weathering is the process of alteration and breakdown of rock
and soil materials at and near the Earth’s surface by chemical decomposition
and physical disintegration).
3. Fabric: (refers to the arrangement of minerals and particles in the rock. The
arrangement may be of similar mineral/particle sizes, composition or
arrangement including showing a preferred orientation).
4. Bedding thickness and inclination.
5. Strength.
6. Discontinuities: (The full description of discontinuities requires attention to
the following: Orientation, Spacing, Persistence, Roughness, Wall Strength,
Aperture, Infill, Seepage, Sets, Block size and shape).

1-Orientation (Attitude of a discontinuity in space (strike, dip direction, and dip
amount).
2-Spacing (perpendicular distance between adjacent discontinuities).
3-Persistence (a discontinuity trace length as observed in an exposure).
4-Roughness (inherent surface roughness and waviness of a discontinuity).
5-Wall strength (compressive strength of the adjacent rock walls of a discontinuity).
6-Aperture (perpendicular distance between adjacent rock walls of a discontinuity).
7-Filling (the filling materials that separate the adjacent rock walls of a discontinuity).
8-Seepage (water flow and free moisture visible in individual discontinuities or in the
rock mass as a whole).
9-Number of sets ( the number of the discontinuities sets).
10-Block size and shape (rock block dimensions resulting from the mutual
orientation of intersecting discontinuities sets).

2/ Engineering properties of intact rock according to ISRM
( Brown, 1981)
Physical Properties
1-Water Content
2-Porosity
3-Density
4-Absorption
5-Abrasiveness by Los Angeles Machine
Mechanical Properties
1-Strength
2-Elastic Modulus

The strength of rock substances is divided into:
A- Compressive strength
1- uniaxial compressive strength qu = F / A
2- Schmidt Hammer
B- Tensile strength
1- Brazilian test
2- Point load test
C- Shear strength
Uniaxial compressive strength
Digitalized machine
Hammer Test
Brazilian Test Direct
Sheer Test

3/ Core Logging
1-Total Core Recovery (TCR)
2-Discontinuity Frequency (F)
3-Rock Quality Designation (RQD)
1-Total Core Recovery (TCR): (TCR) is the ratio of the length of core
recovered to the length of drilled)
2-Discontinuity Frequency (F): is the number of natural discontinuities
intersecting a unit length of recovered core.
3- Rock Quality Designation (RQD)

Soil Mechanics
➢Soil mechanics is the application of the laws of mechanics and
hydraulics to engineering problems dealing with sediments and other
unconsolidated accumulations of solid particles produced by the
mechanical and chemical disintegration of rocks regardless of whether
or not they contain an admixture of organic constituents (Terzaghi,
1925).
➢ In general, soils are formed by weathering of rocks.
➢ The physical properties of soil are dictated primarily by the minerals
that constitute the soil particles and, hence, the rock from which it is
derived.
Soil
Mechanics
Soil
Mechanics

➢Weathering
Weathering is the process of breaking down rocks by mechanical and
chemical processes into smaller pieces.
➢ Mechanical weathering may be caused by the expansion and
contraction of rocks from the continuous gain and loss of heat, which
results in ultimate disintegration. Frequently, water seeps into the
pores and existing cracks in rocks. As the temperature drops, the water
freezes and expands. The pressure exerted by ice because of volume
expansion is strong enough to break down even large rocks.
Other physical agents that help disintegrate rocks are glacier ice, wind,
the running water of streams and rivers, and ocean waves.

Mechanical erosion due to ocean waves and wind
at Yehliu, Taiwan (Courtesy of Braja M. Das,
Henderson, Nevada)

➢In chemical weathering, the original rock minerals are transformed
into new minerals by chemical reaction. Water and carbon dioxide
from the atmosphere form carbonic acid, which reacts with the
existing rock minerals to form new minerals and soluble salts. Soluble
salts present in the groundwater and organic acids formed from
decayed organic matter also cause chemical weathering. An example
of the chemical weathering of orthoclase to form clay minerals, silica,
and soluble potassium carbonate follows:

Transportation of Weathering Products
The products of weathering may stay in the same place or may be moved to other places
by ice, water, wind, and gravity.
The soils formed by the weathered products at their place of origin are called residual
soils.
An important characteristic of residual soil is the gradation of particle size. Fine grained
soil is found at the surface, and the grain size increases with depth. At greater depths,
angular rock fragments may also be found.
The transported soils may be classified into several groups, depending on their mode of
transportation and deposition:
1. Glacial soils—formed by transportation and deposition of glaciers.
2. Alluvial soils—transported by running water and deposited along streams.
3. Lacustrine soils—formed by deposition in quiet lakes.
4. Marine soils—formed by deposition in the seas.
5. Aeolian soils—transported and deposited by wind.
6. Colluvial soils—formed by movement of soil from its original place by gravity, such
as during landslides.

Definitions of Soil
Engineering definitions
Civil Engineering:
Soil is the earth material that can be disaggregated in water by gentle
agitation.
Construction:
Soil is material that can be removed by conventional means without blasting.
Geologic definition
Soil is all friable materials resulting from either weathering of the underlying
rocks or transported from other places.
Agronomy definition
Soil consists of the thin layers of the earth’s crust formed by surface
weathering that are able to support plant life.

Soil Types
According to the physical state of soils
A. Non-Cohesive (Cohesionless) soils: (are composed of bulky grains and have
no plasticity)
B. Cohesive soils: (are the soils which adsorbed water and deformed plastically at
varying water content due to the presence of clay minerals)
(mud sticking on shoes in a rainy day when one walk in a field)
According to geotechnical characteristics of soils
A. Collapsing soils: (Collapsing soils are distinguished by their potential to
undergo large decrease in volume upon increase in moisture content even
without increase in external loads).
Coarse grained soils (Friable Sand)
B. Expansive soils: (Expansive soils are distinguished by their potential for great
volume increase upon access to moisture).
Fine grained soils (Claystone)

Soil Particles and Consistency
The description of the grain size distribution of soil particles according to
their texture (particle size, shape, and gradation).
Major textural classes include
gravel (>2 mm);
sand (0.05 –2 mm);
silt (0.002 –0.05 mm);
clay (< 0.002 mm).
Furthermore, gravel and sand can be roughly classified as coarse textured
soils, while silt and clay can be classified as fine textured soils.
➢ Soil consistency is defined as the relative ease with which a soil can be
deformed use the terms of soft, firm, or hard.
➢ Consistency largely depends on soil minerals and the water content.

Procedure For Grain Size Determination
1- Mechanical Sieving: used for particles > 75 μm

US Standard Sieve Number Sieve Opening (mm)
4 4.75
10 2.00
20 0.850
40 0.425
60 0.250
100 0.150
200 0.075
Mr. Abazar M. A. Daoud, MSc in Engineering Geology
Sieve Analysis Test

2-Hydrometer test: used for smaller particles < 75 μm

Example:
❖ An air-dry soil sample weighing 2000 grams (g) is brought to the
soil’s laboratory for mechanical grain-size analysis. The laboratory
data are as follows:
❖Required
A grain-size distribution curve for this soil sample.

Particle-Size Distribution Curve
✓ A particle-size distribution curve can be used to determine the
following four parameters for a given soil:
1. Effective size (D10): This parameter is the diameter in the particle-
size distribution curve corresponding to 10% finer. The effective size
of a granular soil is a good measure to estimate the hydraulic
conductivity and drainage through soil.
2. Uniformity coefficient (Cu): This parameter is defined as
where D60 diameter corresponding to 60% finer.
Cu> 4 Well Graded soil
Cu< 4 Poorly Graded Soil

3. Coefficient of gradation (Cc): This parameter is defined as
Cc = 1-3 Well
Graded Soil

2-Hydrometer test: used for smaller particles < 75 μm
Mr. Abazar M. A. Daoud, MSc in Applied and Engineering
Geology

Clay Minerals
❖Clay minerals are complex aluminum silicates composed of two basic
units: (1) silica tetrahedron and (2) alumina octahedron.
❖ Each tetrahedron unit consists of four oxygen atoms surrounding a
silicon atom.

❖kaolinite consists of repeating
layers of elemental silica-gibbsite
sheets in a 1:1 lattice, as shown in
Figure. Kaolinite occurs a
platelets, each with a lateral
dimension.

❖Illite consists of a gibbsite sheet
bonded to two silica sheets—one
at the top and another at the
bottom. It is sometimes called clay
mica. The illite layers are bonded
by potassium ions.

❖ Montmorillonite has a structure
similar to that of illite—that is,
one gibbsite sheet sandwiched
between two silica sheets.

❖ Besides kaolinite, illite, and montmorillonite, other common clay
minerals generally found are chlorite, halloysite, vermiculite, and
attapulgite.
❖ It needs to be well recognized that the presence of clay minerals in a
soil aggregate has a great influence on the engineering properties of
the soil as a whole.
❖ When moisture is present, the engineering behaviour of a soil will
change greatly as the percentage of clay mineral content increases
❖ For all practical purposes, when the clay content is about 50% or
more, the sand and silt particles float in a clay matrix, and the clay
minerals primarily dictate the engineering properties of the soil.

Specific Gravity (Gs)
❖ Specific gravity is defined as the ratio of the
unit weight of a given material to the unit
weight of water.
❖ The specific gravity of soil solids is often
needed for various calculations in soil
mechanics. It can be determined accurately in
the laboratory.

Procedure for Consistency Limits
Non Plastic Sand Soil
Atterberg (1911) mentioned that a fine grained soil can exist in four states based on
its water content, namely liquid, plastic, semi solid, and solid states.
The water content at which the soil changes from one state to the other are know as
Consistency limits or Atterberg limits.

Liquid Limits
Plastic Limit

Elements of Soil Mechanics
➢ Index properties:
Index properties mean the observable physical and geotechnical
characteristics with significant influence on a soil’s behaviour.
➢ Index properties include the descriptions of:
Soil particles;
Specific Gravity;
Moisture content;
Soil density;
Soil consistency;
Shear strength;
Collapsing potentiality for collapsing soils;
Swelling potentiality for expansive soils.

➢ Water Content Determination
1-Oven Drying Method
➢ Specific Gravity Determination
1-Measuring Flask Method
➢ Unit Weight Determination
1-Water Displacement Method
2-Proctor Compaction Test
3-Sand Replacement Method (Sand Cone Test)
4-Core Cutter Method

Investigation of subsurface soil in the field
➢Methods used to provide information on subsurface stratigraphy and
soil type include the standard penetration test (SPT) with recovery of
disturbed samples, electric cone penetration test (CPT) and piezocone
penetration test (CPTu).
SPT CPT
CPTu

Components of Soils
➢ Soils contain three components, which may be characterized
as solid, liquid, and gas.
➢ The solid components of soils are weathered rock and
(sometimes) decayed vegetation.
➢ The liquid component of soils is almost always water (often
with dissolved matter), and the gas component is air.
➢ The volume of water and air combined is referred to as the
void.

Weight–Volume Relationships

➢ The volume relationships commonly used for the three phases in a
soil element are void ratio (e), porosity (n), and degree of saturation
(s).
1) Void ratio (e): is defined as the ratio of the
volume of voids to the volume of solids.
2) Porosity (n): is defined as the ratio of the
volume of voids to the total volume.
3) The degree of saturation (S) is defined as
the ratio of the volume of water to the volume
of voids
Abazar
M.
A.
Daoud,
MSc
in
Applied
and
Engineering
Geology

❖ The relationship between void ratio and porosity can be:
❖ The common terms used for weight relationships are moisture
content and unit weight.
4) Moisture content (Mc) is also referred to as
water content (Wc) and is defined as the ratio of
the weight of water to the weight of solids in a given
volume of soil.
5) Unit weight (g) is the weight of soil per unit volume
Abazar
M.
A.
Daoud,
MSc
in
Applied
and
Engineering
Geology

✓ The unit weight can also be expressed in terms of the weight of soil
solids, the moisture content, and the total volume.
✓ Often, to solve earthwork problems, one must know the weight per
unit volume of soil, excluding water. This weight is referred to as the
dry unit weight (γd):
❑ The relationship of unit weight, dry unit weight, and moisture content
can be given as:

❑ Unit weight is expressed in
English units (a
gravitational system of
measurement) as pounds
per cubic foot (lb/ft3).
❑ In SI (Système
International), the unit
used is kilo Newtons per
cubic meter (kN/m3).
❑ The SI unit of mass density
is kilograms per cubic
meter (kg/m3). We can
write the density equations:

Relationships among Unit Weight, Void Ratio,
Moisture Content, and Specific Gravity
Abazar
M.
A.
Daoud,
MSc
in
Applied
and
Engineering
Geology

Industrial Minerals and Rocks
Industrial minerals and rocks are a group of naturally
occurring, mostly non-metallic minerals and rocks, including
materials of sedimentary, metamorphic and igneous rocks such
as sand and gravel, clay stones and limestone, dolomite,
granite, basalt, serpentinite and quartzite, feldspars, phosphate,
sulfur and sulphates.
At an appropriate opportunity cost these materials are of great
economic value as main raw materials for the construction,
glass, abrasive, paper, chemical, ceramics, metallurgical and
agricultural industries.
Industrial
Minerals
Industrial
Minerals

➢ Industrial minerals may be classified into the following three groups:
1. Construction materials, includes sand, gravel, clays and stone
(e.g., limestone, dolomite, granite, serpentinite and quartzite). Stone
is both a source of crushed and dimension stone.
2. The second group, referred to as process materials, includes a
wide range of minerals and rocks possessing special characteristics
that allow them to be used in specialized areas. This group includes
(i) Ceramic materials made up mainly of clays but also silica,
limestone, dolomite, feldspar, quartz, and bauxite;
(ii) Abrasive materials like garnet, silica, and especially chalcedony,
chert, quartz, quartzite, sandstone, and silica sand.
(iii) Refractory and metallurgical materials like magnesite, fire clay,
graphite, bauxite, silica, and dolomite.

3. Materials in the third group include Optical materials like
quartz; absorbent materials like attapulgite, bentonite and
diatomite; fillers like asbestos, bentonite, gypsum, kaolin,
limestone, and vermiculite; glass materials like glass sands,
soda ash, limestone, dolomite, feldspar, borax, and gypsum;
and oil drilling materials like asbestos, barite, attapulgite,
bentonite, limestone and dolomite. Materials in this group are
valued mostly for their physical properties.

Research and Seminar
1) Laterite and Bauxite Formation.
2) Clay Minerals.
3) Building Materials in Red Sea State.
4) Some Geological Effects on the Mechanical Properties of
Different Types of Rocks.

Introduction to Engineering Geology S6.pdf

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