2. 1.What is deformation? What causes it? We
say that a rock has been deformed if it has
undergone what?
Deformation: The change in volume and shape of a
rock when it is subjected to stresses such as gravity,
temperature change and horizontal plate movement.
When rocks deform in response to imposed stress
they exhibit strain, which is the differential change in
size, shape, or volume of a material. Materials differ
in their responses to stress, depending upon
composition, conditions of temperature and confining
pressure, and strain rate
3. Causes of deformation
๏ Temperature change; this cause thermal expansion and
contraction that can cause a rock to fracture. - At high
temperature molecules and their bonds can stretch and
move, thus materials will behave in more ductile manner.
At low Temperature, materials are brittle
๏ Accumulation of thick layers of segment; this can exert an
immense downward pressure on rocks that are buried
underneath.
๏ Folding and faulting; folding is a ductile behavior of which
planar (flat) layers of rock bend in response to stress
๏ Confining Pressure - At high confining pressure materials
are less likely to fracture because the pressure of the
surroundings tends to hinder the formation of fractures.
๏ Strain rate -- At high strain rates material tends to fracture.
Evidence of deformation that has occurred in the past is
very evident in crustal rocks
4. 2. How does stress and strain differ?
How are they similar?
Difference between stress and strain.
๏ Stress is pressure per unit area applied to a rock or solid. While Strain is the deformity or
change in dimension of the rock as a proportion of the original dimension thus being a
dimensionless.
๏ Stress have magnitude and direction measured in Pascalโs or Newton per meter while
strain is dimensionless quantity.
๏ Stress is force on a material while strain is what happens to a material under a given
stress.
Similarities of stress and strain.
๏ Stress and strain are physical properties of a material when it is put under pressure or
load is applied to it. A solid, when it is put under pressure, has the ability to get
deformed.
๏ Both stress and strain are important properties of rocks that explain deformation in rocks
and formation of new layers of rocks over a longtime scale.
๏ Strain in a body is directly proportion to the stress it is put under within its elastic limits.
5. 3.How is stress different from force? What is the
equation for stress? What is the equation for strain?
What is Force?
๏ A force is a push or pull upon an object resulting from the object's
interaction with another object. Whenever there is an interaction
between two objects, there is a force upon each of the objects. When
the interaction ceases, the two objects no longer experience the
force. Forces only and only exist as a result of an interaction. It may
be external, internal, intra-surface/molecular/particles etc. Its unit is
Newton.
๏ 1Newton = 1 kg-m/s^2
๏ Force can be of several types- Frictional Force, Gravitational Force,
Tension Force, Electrical Force, Normal Force , Magnetic Force ,
Applied Force ,Spring Force and many more types.
๏ Whereas Stress is an internal resistance to provide by the body itself
whenever it is under some kind of deformation, this deformation may
due to mechanical causes or thermal cause(provided in case of
thermal, deformation is not allowed).
6. How is stress different from force? What is the
equation for stress? What is the equation for
strain?
๏ Stress is always internal because it is resistance offered
only when the external force tries to deform the body.
One thing is worth noticing here that Force is not the
cause of stress(though its unit is force per area), instead
strain is the cause of stress.
๏ Mathematically, ๐๐ก๐๐๐ ๐ =
๐น๐๐๐๐
๐ด๐๐๐
Its unit is
Pascal or N/m^2
๏ Stress must not be confused with Pressure; generally
people think both pressure and stress are same thing.
No, both are entirely different from each other in all
manners, except units.
๏ Pressure is always externally applied force per unit area.
This may or may not cause the deformation in the body,
whereas stress is an internal resistance offered by the
body against any kind of deformation.
7. 4. Compare and contrast
๏ง Ductile deformation is where a rock behaves in a ductile or plastic manner and
bends while under stress and does not return to its original shape after relaxation
of the stress. Ductile materials deform a lot before they break.
๏ง Brittle deformation is where rocks exhibiting brittle behavior will fractural/break at
stresses higher than its elastic limit. Brittle materials do not deform or deform
very little before it breaks.
๏ Similarities between brittle and ductile
deformation.
๏ง They both occur due to temperature and pressure changes.
๏ง They both lead to change in shape of the rocks.
๏ง They both occur within the earthโs surface.
๏
๏
8. QUESTION FOUR
๏ Ductile deformation warns first before breaking
while brittle deformation fails with little or no
warning.
๏ Occurrence of Ductile deformation is much
favored by high temperatures compared to brittle
deformation.
๏ Normally ductile deformation occurs deep in the
earthโs surface while brittle deformation occurs
close or on the surface of the earth.
๏ Ductile deformation occurs at high pressure
conditions compared to brittle deformation which
occurs at low pressure conditions.
9. QUESTION FIVE
Definition - What does Elastic Deformation mean?
๏ Elastic deformation refers to a temporary deformation of
a material's shape that is self-reversing after removing
the force or load. Elastic deformation alters the shape of
a material upon the application of a force within its elastic
limit. This physical property ensures that elastic materials
will regain their original dimensions following the release
of the applied load. Here deformation is reversible and
non-permanent.
๏ An example of elastic deformation of metals and
ceramics is commonly seen at low strains; their elastic
behavior is generally linear. Another c example of elastic
deformation, and indeed, of highly elastic behavior, is a
rubber band: it can be deformed to a length many times
its original size, but upon release, it returns to its original
10. QUESTION SIX
Terms used to describe stress
๏ Tension: this is stress that acts to lengthen an object.
๏ Normal stress: this is stress that acts perpendicular to a surface.
๏ Hydrostatic: this is stress (usually compressional) that is uniform in all direction. Stress in
the
๏ Earth is nearly hydrostatic.
๏ Shear: this is stress that acts parallel to a surface; it can cause one object to slide over
another
๏ Compression: This is stress that acts to shorten an object.
Terms used to describe stress
๏ Longitudinal or linear strain; strain that changes the length of a line without changing its
direction can either be compressional or tensional.
๏ Tension; longitudinal strain that lengthens an object.
๏ Infinitesimal strain; strain that is tiny, a few percentage allows a number of useful
mathematical
๏ simplifications and approximations.
๏ Finite strain; strain larger than a few percent requires a more complicated mathematical
๏ treatment than infinitesimal strain.
๏ Homogeneous strain; uniform strain, Straight lines in the original object remain straight
and,
๏ Parallel lines remain parallel.
11. 7.STRIKE AND DIP
๏ Strike and dip are measurements of the orientation and slope of
a rock.
๏ The dip of a rock is the angle between horizontal and the slope
of the rock.
๏ The strike of a rock is the orientation of a horizontal line drawn
perpendicular to the dip.
12. STRIKE AND DIP
๏ Strike and dip are used to describe the orientation
of a rock bed, fault, fracture, cuestas, igneous
dikes, and sills.
๏ Planes can be defined in space by their
inclination or dip and their strike, the bearing of
the line of intersection of the plane and a
horizontal surface.
๏ Geologists use these measurements to map
geologic structures.
13. QUESTION EIGHT
๏ A joint is a break of natural origin in the continuity of either a layer or body of rocks
that lacks any visible or measurable movement parallel to the surface of the fracture
๏ The inclination of a joint plane with the horizontal is called the dip of the joint.
๏ The line along which the joint plane meets the surface is called the strike of the joint,
the
strike direction being perpendicular to the dip direction.
๏ Examples of joints;
๏ Sheet joints: These are horizontal joints developed in massive igneous rocks,
especially granite.
They divide the rocks into sheets. These horizontal joints are closely spaced in the
upper layers
and become progressively further apart with depth.
๏ Dip joints: These are joints in which the strike of the joints is perpendicular to the
strike of the
beds.
Shear joints: These are joints formed by the shearing stresses, which tend to slide
one part of the rock against the other. These joints are developed during folding.
Strike joints: These are joints in which the strike of the joints is parallel to the strike of
the bed.
Oblique joints: These are joints in which the strike of the joints is neither parallel nor
normal to
the strike of the bed.
14. 9. Using illustrations describe faults. What are the 3 main types of
faults? Which form due to extension? contraction? shear?
A geologic fault is a more-or-less planar (flat) fracture along which the rocks
on either side have slid past each other. The sliding surface is also known as
the fault plane, or the fault surface.
Types of faults
1. Dip-Slip Faults
If rocks slide directly up or down the fault plane, the movement is called dip-
slip. That kind of movement results in the same rock layers being higher on
one side than the other. Dip-Slip Faults occur as normal or reverse faults.
Dip-slip faults are formed as a result of compression
2. Strike-Slip Faults
In a strike-slip fault, the blocks on either side of the fault move laterally but not
vertically with respect to one another in a direction parallel to the fault. Strike-
slip faults can be categorized as right or dextral and left or sinistral according
to their direction of motion .Strike-slip faults are formed as a result of tension
3. Oblique fault
An oblique fault combines elements of a dip-slip fault and a strike-slip fault. It
is caused by a combination of shearing and tension or compressional forces.
Nearly all faults will have some component of both dip-slip (normal or reverse)
and strike-slip, so defining a fault as oblique requires both dip and strike
15. QUESTION TEN
๏ Folds are bends or undulations or wavelike
features in layered rocks of the earthโs crust, as a
result of the stresses (commonly lateral
compression) to which these rocks have been
subjected
to, from time to time in the past history of the
Earth. Folded rocks can be compared to several
layers of rugs or blankets that have been pushed
into a series of arches and troughs. The fact that
rock is folded shows that it was strained in a
ductile way rather than by elastic or brittle strain.
16. TYPES OF FOLDS
๏ Anticline
๏ Syncline
๏ Monocline
๏ Chevron
๏ Recumbent
๏ Isoclinal
๏ Plunging
๏ Dome and Basin
๏ Ptygmatic
17. QUESTION ELEVEN
๏ A geological fold occurs when one or a stack of originally flat and planar surfaces,
such as sedimentary strata, are bent or curved as a result of permanent deformation.
Changes in shape and volume occur when stress and strain causes the rock to buckle
and fracture or crumple into folds.
๏ Causes of Geological Folds
๏ Tectonic pressure and stress;
๏ The folds arise as a result of the tectonic pressure and stress in the rocks rather
than fracture, they fold. They are easily visualized by the loss of horizontality of the
strata. When tectonic forces acting on sedimentary rocks are a number of
characteristic forms. Sedimentary rocks are more flexible than the metamorphic, and
when the thrust is not intense enough to move them fold as if they were a piece of
paper.
๏ None-Tectonic causes of folding. These include all those rock folding effects which
are effective over the ground surface, resulting, mainly under the influence of
gravitational force, such as Land sliding , Differential compaction , Creeping (a gradual
movement of rock and debris down a slope or a slow deformation of rocks and
minerals in response to prolonged stress.
๏ The possible causes of rock switching between the two ways of formation are
stipulated below;
๏ Tectonic plate movements
๏ Volcanic activity
๏ Subduction
18. QUESTION TWELVE
๏ Foliations are characteristics of tectonites which
are rocks whose structure are the product of
deformation and are commonly but not
necessarily metamorphosed.
๏
Secondary foliation is as a result of
microscopically penetrative deformation and
distortion of
sedimentary volcanic or intrusive igneous rocks
usually under metamorphic conditions
19. 10.Discuss the engineering implications of folds,
faults and joints in rock masses?
The following are the various effects produced by folded rocks: -
๏ท Fractured folded rocks are highly permeable, and as such may pose
numerous problems; like, while excavating tunnels through such
regions, ground water may rush into the excavation.
๏ท Since the folded rocks offer greater prospects for groundwater, they
become quite important for engineers searching for water supplies.
๏ท The anticlinal folds provide good prospects for stored petroleum; and
hence in oil exploration, folds must not be overlooked.
๏ท Synclinal folded rocks may yield hard and tough quality stones,
whereas, anticlinal folded rocks will yield weaker stones.
๏ท Folded rocks are under considerable strain, and hence, excavations
through them may be accompanied by slips and rock bursts.
๏ท Folded rocks are generally shattered and weak, particularly in the
axial regions; hence, they are unsafe to be trusted as roofs or floors of
tunnels, or as foundations for dams. Such regions should therefore, be
avoided for such purposes, or must be thoroughly investigated,and
remedial measures taken, if at all adopted for such uses.
20. Engineering implications of joints in rock masses
๏ The joints in rocks play a very important role in landslide in hilly
regions, because
they serve as slip surfaces.
The effects of joints on the proposed structure should, therefore,
be thoroughly considered and
remedial measures undertaken, before the actual construction of
the structure. Treatment of joints
will differ in different projects. E.g. when leakage is to
be avoided, grouting of joints is generally adopted. Similarly,
when the jointed rocks offer
instability or unsafe, as in the case of heavily jointed roofs of
tunnels, lining of tunnels may
become necessary. In addition to all these engineering problems,
study of joints becomes
important in quarrying and mining operations. In quarrying of
stones, joints may help in making
quarrying easier, if quarrying is done along them.
21. Engineering implications of faults in rock masses
Faulted rocks generally offer unstable sites from engineering
considerations, not only because there have been displacements along
the fault(s) in the past, but also that further fresh movements may take
place at any time in the future. Thus, if a structure is constructed on
such rocks, then any future movements along the faulted plane(s) may
endanger the stability of the
structure, and thus causing it to collapse. An engineer, as a general
rule, must try to avoid locating any of the proposed structures on fault
or rather even in its vicinity. When an engineer decides to put the
proposed project in moderately faulted regions, precautions must be
taken to avoid any major failures, either by seismic effects caused by
movements along the faults, or due to heavy leakage that may take
place through the faulted rocks. The improvement works in faulted
rocks, such as excavation of weaker material from the faulted zone and
refilling or grouting it with cement concrete, etc. may therefore become
necessary.
