Engineering geology

1. GROUP 4 GEOLOGY
REPORT

2. ATTITUDE OF BEDS
• Geologists take great pains to measure and record geological structures
because they are critically important to understanding the geological
history of a region. One of the key features to measure is the orientation,
or attitude, of bedding. We know that sedimentary beds are deposited in
horizontal layers, so if the layers are no longer horizontal, then we can
infer that they have been affected by tectonic forces and have become
either tilted, or folded. We can express the orientation of a bed (or any
other planar feature) with two values: first, the compass orientation of a
horizontal line on the surface—the strike —and second, the angle at which
the surface dips from the horizontal, (perpendicular to the strike)—the dip

3. DIP – IT IS DEFINED AS THE AMOUNT OF INCLINATION OF A BED WITH RESPECT TO A
HORIZONATAL PLANE. THIS IS MEASURED ON A VERTICAL PLANE LYING AT RIGHT
ANGLED TO THE STRIKE OF THE BEDDING.

4. TYPES OF DIP
True Dip – It is the maximum amount of slope along a line perpendicular to
the strike, in other words, it is the maximum slope with respect to the
horizontal. It may also be stated as the geographical direction along which
the line of quickest descent slopesdown.
Apparent Dip – Along any direction other than that of the true dip, the
gradient is scheduled to be much less and therefore it is defined as the
apparent dip. The apparent dip of any bed towards any direction must
always be less than its true dip.

5. STRIKE
Strike is generally defined as the line of intersection between a
horizontal plane and the planar surface being measured. It is found by
measuring the compass direction of a horizontal line on the surface.

6. Strike and dip are often easier to see on an
exposure of rock than on a map, as the above
photograph shows. Geologists use strike and
dip symbols on geologic maps to show strikes
and dips measured in the field. The geologic
map (left) shows many strike and dip symbols.
A GEOLOGIC MAP is used to show rock units or geologic strata that
are exposed at the surface. Bedding planes and structural features
such as faults, folds, foliations, and lineations are shown with strike
and dip or trend and plunge symbols which give these features' three-
dimensional orientations.

7. IMPORTANCE OF DIP AND STRIKE
- To determine the younger bed of formation. It is well known that younger
beds will always be found in the direction of dip. If we go in the direction
of dip, relatively beds of younger age will be found to out-crop and older
rocks in the opposite direction.
- In the classification, and nomenclature of folds, faults, joints and
unconformities, the nature of dip and strike is of paramount significance.
Thus the attitude, which refers to the three dimensional orientation of
some geological structures, is defined by their dip and strike

8. MEASURING STRIKE AND DIP
The strike and dip of
planar geologic structures,
such as bedding, faults,
joints and foliations, can
be determined by several
methods with the Brunton
compass.
MEASURING
STRIKE MEASURING
DIP

9. FOLDS, FAULTS , JOINTS

10. FAULT A fault is a break in the rocks that make up the earth's crust, along
which on either side rocks move pass eachother. Larger faults are
mostly from action occuring in earth's plates. A fault line is the trace
of a fault, or the line of intersection between the fault line and the
earth's surface
Stike-slip faults are vertical (or nearly vertical)
fractures where the blocks have mostly moved
horizontally. If the block opposite an observer
looking across the fault moves to the right, the slip
style is termed right lateral; if the block moves to
the left, the motion is termed left lateral.

11. Dip-slip faults are inclined fractures where
the blocks have mostly shifted vertically. If the
rock mass above an inclined fault moves
down, the fault is termed normal, whereas if
the rock above the fault moves up, the fault is
termed reverse
A transform fault is a special variety of
strike-slip fault that accommodates
relative horizontal slip between other
tectonic elements, such as oceanic
crustal plates. Often extend from
oceanic ridges.

12. FOLD
S
A fold is when one or more originally bent
surfaces are bent or curved as the result of
permanent deformation.
Folding and Warping
Syncline and anticline are
terms used to describe folds
based on the relative ages of
folded rock layers. A syncline is
a fold in which the youngest
rocks occur in the core of a fold
(i.e. closest to the fold axis),
whereas the oldest rocks occur
in the core of an anticline.

13. TYPES OF FOLDS
Anticline: Linear with dip away from the center
Syncline: Linear with dip towards the center
Monocline: Linear with dip in one direction between horizontal layers
on each side.
Basin: Non-Linear with dip towards all center directions.
Dome: Non-Linear with dip away from center in all directions.

14. JOINT
S
a joint is a fracture dividing rock into two sections that moved away from
each other. A joint does not involve shear displacement, and forms when
tensile stress breaches its threshold. In other kinds of fracturing, like in a
fault, the rock is parted by a visible crack that forms a gap in the rock.

15. TYPES OF JOINTS
SYSTEMATIC JOINTS: have a
subparallel orientation and regular
spacing
JOINT SET: joints that share a
similar orientation in same area
JOINT SYSTEM: two or more joints
sets in the same area
NONSYSTEMATIC JOINTS: joints
that do not share a common
orientation and those highly curved
and irregular fracture surfaces.

16. Bedding planes are of great importance to Civil engineers. They are planes of structural
weakness in sedimentary rocks, and masses of rock can move along them causing rock
slides. Since over 75 percent of the earth’s surface is made up of sedimentary rocks,
civil engineers can expect to frequently encounter these rocks during construction.
Undisturbed sedimentary rocks may be relatively uniform, continuous, and predictable
across a site. These types of rocks offer certain advantages to civil engineers in
completing horizontal and vertical construction missions. They are relatively stable rock
bodies that allow for ease of rock excavation, as they will normally support steep rock faces.
Sedimentary rocks are frequently oriented at angles to the earth’s “horizontal” surface;
therefore, movements in the earth’s crust may tilt, fold, or break sedimentary layers.
Structurally deformed rocks add complexity to the site geology and may adversely affect
construction projects by contributing to rock excavation and slope stability problems.
Engineering Construction and The Study of Beds

17. ROCK MECHANICS
PHYSICAL AND MECHANICAL PROPERTIES OF ROCKS

18. PHYSICAL PROPERTIES
a. POROSITY- is the percentage of void space
in a rock. It is defined as the ratio of the
volume of the voids or pore space divided by
the total volume. It is written as either a
decimal fraction between 0 and 1 or as a
percentage. For most rocks, porosity varies
from less than 1% to 40%

19. b. PERMEABILITY is the property of rocks that is an
indication of the ability for fluids (gas or liquid) to flow
through rocks. High permeability will allow fluids to
move rapidly through rocks. Permeability is affected by
the pressure in a rock.
DENSITY varies significantly among
different rock types because of
differences in mineralogy and porosity.
Knowledge of the distribution of
underground rock densities can assist in
interpreting subsurface geologic
structure and rock type. Rocks are
generally between 1600 kg/m3
(sediments) and 3500 kg/m3 (gabbro).

20. CLASSIFICATION OF ROCK HARDNESS
CLASSIFICATION FIELD TEST RANGE OF COMPRESSSIVE
STRENGTH (MPa)
Very soft rock Can be peeled with a knife, material
crumbles under firm blows
with the sharp end of a geological
pick.
1-3
Soft rock Cannot be scraped with a knife,
indentations of 2-4 mm with firm
blows of the pick point.
3-10
Medium hard rock Cannot be scraped or peeled with a
knife, hand held specimen
breaks with firm blows of the pick.
10-25
Hard rock Point load tests must be carried out in
order to distinguish
between these classifications. These
results may be verified by
uniaxial compressive strength tests on
selected samples
25-70
Very hard rock 70-200
Extremely hard
rock
>200
c. HARDNESS is the subjective description of the resistance of an earth material to permanent
deformation, particularly by indentation (impact) or abrasion (scratching) .

21. d. STRENGTH-Strength is the ability of a material to resist deformation induced by external forces. The
strength of a material is the amount of applied stress at failure (ASTM
D653). The laboratory uniaxial (unconfined) compressive strength is the standard strength parameter of
intact rock material.
• Tensile strength- is extremely
difficult to measure: It is direction-
dependent, flaw-dependent, sample
size-dependent,…
• An indirect method , the Brazilian
disk test is used. The Brazilian test is
a technique used to evaluate the
tensile strength of brittle materials
like concrete or rocks. The
experiment consists in compressing
a circular disk along its vertical
diameter in order to induce tensile
failure at the center of the disk

22. Compressive strength-
Compressive strength or
compression strength is the
capacity of a material or
structure to withstand loads
tending to reduce size, as
opposed to tensile strength,
which withstands loads
tending to elongate.
The Uniaxial
Compressive Strength of
Soft Rock. Soft rock is a
term that usually refers to a
rock material with a uniaxial
compressive strength (UCS)
less than 20 MPa.
Uniaxial compressive test equipment

23. Shear strength- shear strength is the strength of a material or component against the type of
yield or structural failure when the material or component fails in shear. A shear load is a
force that tends to produce a sliding failure on a material along a plane that is parallel to the
direction of the force. When a paper is cut with scissors, the paper fails in shea

24. e. ELASTICITY- Elasticity is the property of matter that causes it to resist deformation in
volume or shape. Some of the deformation of a rock under stress will be recovered when
the load is removed. The recoverable deformation is called elastic and the non-recoverable
part is called plastic deformation.
Commonly, the elastic deformation of rock is directly proportional to the applied
load. The ratio of the stress and the strain is called modulus elasticity.

25. f. PLASTICITY - ability of certain solids to flow or to change shape permanently when
subjected to stresses of intermediate magnitude between those producing temporary
deformation, or elastic behavior, and those causing failure of the material, or rupture
(see yield point).
Plasticity enables a solid under the action of external forces to undergo
permanent deformation without rupture. Elasticity, in comparison, enables a
solid to return to its original shape after the load is removed. Plastic
deformation occurs in many metal-forming processes (rolling, pressing, forging)
and in geologic processes (rock folding and rock flow within the earth under
extremely high pressures and at elevated temperatures).

26. For example, a solid piece of metal being bent or pounded into a new shape
displays plasticity as permanent changes occur within the material itself. In
engineering, the transition from elastic behavior to plastic behavior is called
yield.
Plastic deformation is observed in most materials, particularly metals,
soils, rocks, concrete, foams, bone and skin.

27. ELASTIC WAVES AND
ROCK PROPERTIES

28. Stress is force per unit area. Imagine a particle represented by an infinitesimally small
volume around a point within a solid body with dimensions (dx, dy, dz)
Strain is deformation measured as the fractional change in dimension or volume induced
by stress. Strain is a dimensionless quantity.
Static -concerned with bodies at rest or forces in equilibrium.
Dynamic- a force that stimulates change or progress within a system or process.
Terminology

29. DETERMINING DYNAMIC ROCK
PROPERTIES
I-Typical Rock Properties
• Modulus of Deformation –
Young’s Modulus - E
• Modulus of Rigidity – Shear
Modulus – G
• Modulus of Volume
Expansion – Bulk Modulus - K
• Poisson’s Ratio - μ
• Bulk Density – ρ
• Compressive Strength – σC
• Tensile Strength – σT
II-Rock Properties Referenced to Blasting Actions
• Young’s Modulus is a measure of the resistance of a solid to transmit
load
allows transmission of longitudinal stress from shock wave impact
• Bulk Modulus is a measure of the resistance of a solid to change in
volume
allows transmission of transverse stress resulting from shock wave
impact
• Poissons’ ratio defines the amount of borehole expansion that can occur
under dynamic loading just before rock/ore failure
maximum amount of ‘hoop’ stress that can be tolerated before cracks
are generated
• Compressive strength dictates the level of crushing that will occur at the
borehole wall
• Tensile strength dictates the level of tensile stress when crack formation
will occur
Can have supersonic cracking as well as interstitial cracking

30. III- Dynamic or Static
• Fragmentation of rock/ore is a dynamic process, not a static one
• Rock/ore appears to be much stronger in the dynamic case, than the static one (rule
of thumb is to assume that dynamic such as compressive and tensile strength are
twice the values of static properties)
• Degree of fit (correlation with measurement properties) is better with dynamic
rock/ore parameters
• Easier and less expensive getting dynamic rock properties using dynamic loading
such as detonating explosive charges
• Rock/ore core strength values do not appear to correlate well with dynamic values
• Dynamic properties are preferred in computer models relating the dynamic
processes of blasting action to dynamic properties of the material being blasted

31. Wave velocities in a rock are computed from wave propagation
travel times from sonic logs. Elastic wave velocity is a powerful
parameter used to interpret the physical properties underlying the
rock. However, a range of geological rock properties affect wave
velocities. Understanding the microstructural, fluid, stress, and
mineralogical controls on elastic wave velocities is at the center of
laboratory experiments on the rock core.
WAVE VELOCITIES IN A ROCK

32. SEISMIC WAVES TYPES
Seismic waves--- are elastic waves that propagate in the earth.
P-waves ---(or equivalently, compressional waves, longitudinal waves, or
dilatational waves) are waves with particle motion in the direction of wave
propagation.
S-waves--- (or equivalently, shear waves, transverse waves, or rotational waves)
are waves with particle motion in the direction perpendicular to the direction of
wave propagation.

33. Seismic wave
velocities change over
a wide range in
nature, even for the
same rock type, since
several factors control
the velocity of a
specified medium.
This phenomenon
generally prevents
defining the
subsurface lithology
by seismic velocities
only.
Velocity Analysis

34. For instance, measured P wave velocities of sandstones
range from 1.8 to 4.8 km/s depending on several factors,
including
• Lithology
• Saturation and fluid type
• Porosity
• Cementation, grain size and pore shape
• Age of the rock
• Pressure/compaction or depth
• Density of the medium
• Temperature
• Frequency of the seismic signal
• Anisotropy and fractures
• Clay content
• Consolidation

35. From the definitions of the P- and S-wave
velocities , note that both are inversely
proportional to density ρ. At first thought,
this means that the lower the rock density
the higher the wave velocity. A good
example is halite which has low density
(1.8 gr/cm3) and high P-wave velocity
(4500 m/s). In most cases, however, the
higher the density the higher the velocity
This is because an increase in density
usually is accompanied by an increase in
the ability of the rock to resist
compressional and shear stresses.

36. So an increase in density usually implies an increase in bulk
modulus and modulus of rigidity. Note that the greater the bulk
modulus or the modulus of rigidity, the higher the velocity.

37. Based on field and laboratory measurements, Gardner [1] established an empirical
relationship between density ρ and P-wave velocity α. Known as Gardner’s formula
for density, this relationship given by ρ = cα0.25, where c is a constant that depends
on the rock type, is useful to estimate density from velocity when the former is
unknown. With the exception of anhydrites, most rock types — sandstones, shales,
and carbonates, tend to obey Gardner’s equation for density.

38. THREE INDIRECT WAYS TO ESTIMATE THE
S-WAVE VELOCITIES
The first approach is to perform prestack amplitude
inversion to estimate the P- and S-wave reflectivities and
thus compute the corresponding acoustic impedances
(analysis of amplitude variation with offset).
The second approach is to record multicomponent seismic
data and estimate the S-wave velocities from the P-to-S
converted-wave component (4-C seismic method).
The third approach is to generate and record S-waves
themselves.

39. STATIC AND DYNAMIC MODULI OF ELASTICITY
-The dynamic moduli of rock are those calculated from the elastic- wave velocity
and density. Usually refers to the elastic stiffness that can be derived from elastic
wave velocities in combination with density.
-The static moduli are those directly measured in a deformational experiment.
Also refers to the elastic stiffness that relates deformation to applied stress in a
quasi-static loading situation, that is the slope of the stress–strain curve.

40. Modulus of elasticity :
The ratio of the stress in a body to the
corresponding strain (as in bulk modulus, shear
modulus, and Young's modulus) — called also
coefficient of elasticity, elastic modulus. An elastic
modulus is a quantity that measures an object or
substance's resistance to being deformed
elastically when a stress is applied to it. The elastic
modulus of an object is defined as the slope of its
stress–strain curve in the elastic deformation
region: A stiffer material will have a higher elastic
modulus.
The three types of elastic constants are:
Modulus of elasticity or Young's modulus (E), Bulk
modulus (K) and. Modulus of rigidity or shear
modulus

41. GROUTING
WHAT IT IS:
Rock grouting is the injection
of specially formulated
cement-based mixes into the
ground to improve its
strength or reduce
permeability. The principle of
grouting is to fill the open
voids existing in a rock mass
in introducing, by pressure
through boreholes, a certain
amount of a "liquid" matter,
in fact a suspension, that will
harden later on. The
properties of the grouted
rock complex should be
modified in the desired way.

42. HOW IT WORKS:
It’s most commonly performed by drilling holes into the underlying rock to intercept open cracks, joints,
fissures or cavities, then pumping under pressure balanced and stabilized grout mixes using a combination
of cement, water, and additives. For larger, more complex projects, enhanced quality control is available
through real-time computer monitored grouting software called GROUT I.T.
WHY YOU NEED IT:
Rock grouting can be used to decrease water flow through fractured rock, plus it can be performed in areas
with space constraints. It is mostly used for dams, tunnels, reservoirs and shafts.