PANGASINAN STATE UNIVERSITY

URDANETA CITY CAMPUS

COLLEGE OF ENGINEERING & ARCHITECTURE
CIVIL ENGINEERING DEPARTMENT
1st SEM, A.Y. 2023-2024

REPORT ON STRUCTURAL GEOLOGY

 STRUCTURAL GEOLOGY AND ITS IMPORTANCE TO CIVIL ENGINEERING

Structural geology is the branch of geology concerned with the study of how rocks
deform and the effects of this deformation. In civil engineering, understanding structural
geology is crucial as it directly impacts the design, construction, and safety of various
infrastructure projects.

IMPORTANCE

● Folds are geological structures in which rock layers have bent due to tectonic forces. In
civil engineering, folding is concerned as it can make the tunneling process difficult.
Tunnels, dams, or roads should be planned and collected on the surface that areas and
rock layers having folds are considered in such a way that the constructed structure’s
durability is always planned in such a way that it has folds in it.
● Fails is a break in the Earth’s crust in which movement has occurred. There should be no
stress in the area from which the force is removed, and that should be planned in such a
way that it has no movement in it. Joints are cracks in rocks with no vertical or side-to-
side motion.
● Joints play critical roles in engineering operations, both positive and negative. To civil
engineers, in particular, joints are points of weaknesses that could predispose rocks to
potential failure and instability in a structure such as dams, tunnels, or highways. Proper
examination of joints is crucial during a design process for the development of
sustainable and economically feasible designs. For instance, joints act as seepage zones
and could lead to rock foundation failure or tunnel lining integrity.

ORIENTATION AND GEOMETRY OF GEOLOGIC STRUCTURES

To measure and describe the geometry of geological layers, geologists apply the
concepts of strike and dip. Strike refers to the line formed by the intersection of a horizontal
plane and an inclined surface. This line is called a strike line, and the direction the line points in
(either direction, as a line points in two opposite directions) is the strike angle. Dip is the angle
between that horizontal plane and the inclined surface (such as a geological contact between
tilted layers) measured perpendicular to the strike line down to the inclined surface.

A useful way to think about strike and dip is to look at the roof of a house. A house’s
roof has a ridge along the top, and then sides that slope away from the ridge. The ridge is like a
strike line, and the angle that the roof tilts is the dip of the roof.

Strike and dip of a roof.

The sloping roof of a building is a useful analogy to

illustrate strike and dip. The ridge of the roof defines the
strike of the roof. The roof dips away from the ridge with a
characteristic angle (the dip angle). The inset in the top
right corner of the figure shows the roof viewed from
above with the strike and dip symbol superimposed on it.
 GEOLOGIC STRUCTURES (FOLDS, FAULTS, JOINTS)

FOLDS

Folds are geologic structures created by ductile (plastic) deformation of Earth’s crust. Folds
are created in rock when they experience compressional stress. This is when the rock is being
pushed inward from both sides. This is like if you put a spring between your hands and push
them together. As you push, you’re compressing the spring, and rock can be compressed in the
same way over long periods of time. There are different types of folds created by compressional
stress depending on which way the rock bends.

Occurrence/Causes:

Folds are caused by deformation in the earth’s layers. Rocks must be ductile and behave
plastically to bend rather than break. Ductile means to be able to deform or change shape
without losing toughness or breaking. The opposite of ductile is brittle, where the material
cannot deform without breaking.

Characteristics:

Folds can be of any size, and it’s very common to have smaller folds within larger folds.
Large folds can have wavelengths of tens of kilometres, and very small ones might be visible
only under a microscope.

Anticlines are not necessarily, or even typically, expressed as ridges in the terrain, nor
synclines as valleys. Folded rocks get eroded just like all other rocks and the topography that
results is typically controlled mostly by the resistance of different layers to erosion.

Example of the topography in an area of folded rocks that has been eroded. In this case
the green and grey rocks are most resistant to erosion, and are represented by hills.
Three types of folds:

• Monocline is a simple fold structure that consists of a bend in otherwise horizontal rock
layers. Anticlines and synclines are more common than monoclines.
• Anticline fold is convex up: the layered strata dip away from the center of the fold. If you
drew a line across it, the anticline would resemble a capital letter “A.”
• Syncline resembles a “U.” It is a concave upward fold in which the layered strata dip
toward the center of the fold.

Faults

Faults are fractures in the earth's crust along which movement has occurred. Faults are
the result of tectonic forces. If rocks on either side of a fracture move in the opposite direction,
it is called a fault. If no displacement occurs, it is called a joint. Faults may range from less than
a centimeter to thousands of kilometers.

Occurrences/Causes

Faults occurred when either side of the fractured rocks moved relatively to each other.
The primary causes of faults are tectonic forces. The earth’s surface consists of giant, slow-
moving blocks of rocks that grind against one another, pushing, pulling, and squeezing
rock layers underneath.

Characteristics

A fault is a weak spot in the earth’s crust where rocks have moved relative to each
other. The movement of a fault can be a few centimeters or thousands of kilometers. The
surface where the movement occurs is called the fault plane, and the amount of the
movement is called the displacement.
Types of Faults

 Normal faults occurs when the hanging wall moves down relative to the footwall. This
type of fault is usually found in areas where the earth’s crust is stretched or pulled apart.
 Reverse faults otherwise known thrust faults occurs when the hanging wall moves
relatively upward towards the footwall. This type of fault is usually found in areas where
the earth’s crust is compressed.
 Strike- slip faults occurs when either side of the rocks slide horizontally past each other.
This type of fault is usually found along boundaries of tectonic plates. As an example,
the San Andreas Fault in California.

JOINTS

Joints are integral components of the Earth's crust, shaping landscapes, influencing
groundwater flow, and impacting engineering projects. They represent the response of rocks to
geological forces and processes, providing valuable insights into the history and behavior of
rock formations. Understanding joints is essential for various scientific disciplines, including
geology, hydrogeology, and engineering, as they play a significant role in shaping our natural
environment and human-made structures.

Occurrence/Causes:

Joints are fractures in rocks where there has been no significant movement. They form
due to factors like cooling, pressure release, or weathering. Joints are prevalent in many rock
types and can be influenced by various geological processes.

They form due to a variety of geological processes:

Tectonic Forces: The Earth's crust is under constant stress due to tectonic forces, such as the
movement of tectonic plates. This stress can cause rocks to fracture, creating joints.

Cooling and Contraction: When molten rock cools and solidifies, it contracts. This contraction
often leads to the formation of joints as the rock adjusts to its new, cooler state. This is
particularly common in igneous rocks like granite.

Pressure Release: Rocks that were buried deep within the Earth's crust may have joints form
when they are exposed at the surface due to erosion or uplift. This sudden release of pressure
can cause the rocks to fracture along joints.
Characteristics:

Joints are typically planar fractures that do not involve significant displacement. They can occur
in various orientations and patterns within rock formations. Joints may affect the strength and
stability of rock masses.

Types:

1. Bedding Joints:

These joints are found in sedimentary rocks and run parallel to the bedding planes.
Bedding planes are essentially the layers or strata within sedimentary rocks. The formation of
bedding joints is often a result of the stress and pressure experienced during the sedimentary
rock formation process.

2. Master Joints:

Typically observed in sedimentary formations, master joints exhibit a distinct pattern.

They run in two directions, usually perpendicular to each other. One set of joints aligns parallel
to the dip direction (the angle of inclination of the rock layers) and the other parallel to the
strike direction (the compass direction of the line formed by the intersection of the rock layer
with a horizontal plane). Among these two sets, one set tends to be more pronounced and
extends over long distances. These prominent and extensively developed joints are termed
master joints.

3. Primary Joints:

These joints are prevalent in igneous rocks and are a consequence of the cooling and
contraction of magma during the rock's formation process. As the molten rock cools and
solidifies, it undergoes contraction, leading to the development of fractures or joints. These
primary joints play a significant role in determining the overall structure and integrity of the
igneous rock formation.

Impact on Engineering:

Joints can influence the stability of rock masses and the behavior of rock slopes. In
engineering, understanding joint patterns is crucial for assessing the risk of rockfalls, landslides,
and other geotechnical hazards. Engineers must consider joint orientations and densities when
designing structures in rock formations. Moreover, Joints play a crucial role in geotechnical
engineering, affecting the strength and stability of rock masses. Understanding joint patterns is
essential for designing structures that can withstand the potential effects of joint-related
hazards such as rockfalls and slope instability.
 REFERENCES:

Earle, S., & Earle, S. (2015, September 1). 12.2 folding. Pressbooks.

https://opentextbc.ca/geology/chapter/12-2-folding/

McBeth, J., Panchuk, K., Prokopiuk, T., Hauber, L., & Lacey, S. (2020, January 8). Overview of

Geological structures Part 1: Strike, Dip, and Structural Cross-Sections. Pressbooks.

https://openpress.usask.ca/geolmanual/chapter/overview-of-strike-dip-and-structural-

cross-sections/

!SYOU co-designed sneakers. (2016, January 11). Structural features fold, fault, joints [Slide

show]. SlideShare. https://www.slideshare.net/Vyankyo/structural-features-fold-fault-

joints

The Editors of Encyclopaedia Britannica. (1998, July 20). Strike | Fault, folding & Earthquakes.

Encyclopedia Britannica. https://www.britannica.com/science/strike-geology