2. What is a rock?
• To geologists, a rock is a natural substance composed of
solid crystals of different minerals that have been fused
together into a solid lump.
• The minerals may or may not have been formed at the
same time. What matters is that natural processes glued
them all together.
• Types of Rocks
1. igneous rocks are volcanic and form from molten
material.
2. Sedimentary rocks are formed from eroded fragments
of other rocks or even from the remains of plants or
animals.
3. Metamorphic rocks are sedimentary or igneous rocks
that have been transformed by pressure, heat, or the
3. What is rock mechanics?
• Rock mechanics is the study of the mechanical behavior of
subsurface sedimentary strata and rocks that are formed. The basic
principle is that rock simply responds to stress by changing in
volume or form. The change in the rock volume or form due to the
applied stress is called strain.
Rock mechanics determines how a particular rock reacts when it is put
to the use required by mankind for buildings, roads, bridges, dams,
tunnels, and other civil engineering
uses. It will assess the bearing capacity
of the rock on the surface and how the
force applied on the rock by the
structures being built on it will affect
the rock at various depths.
4. Rock mechanics
• It is convenient to subdivide rock mechanics into the
following branches:
a) Structural rock mechanics,
which is concerned with the
stability of engineering structures
in which the material is
predominantly rock.
b) Comminution, which is
concerned with the reduction
of rock to small fragments by
the application of external
forces as in drilling, blasting,
cutting and grinding.
5. What is the purpose of rock mechanics?
The purpose of rock mechanics is to understand how and why rock
deforms either as a sporadic or catastrophic event. It is commonly
applied to:
• civil and geological engineering,
• mining,
• drilling, and
• conventional reservoir geohazard
evaluation.
6. What are the characteristics of rock
mechanics?
• Rock mechanical properties mainly include elastic modulus,
Poisson’s ratio, and rock strength. These parameters can be obtained
by lab experiments of core samples or by in-situ tests. The other
characteristics of rocks
include time-dependent
rheological and
creep behaviors
(Wang 1981).
7. 5 main characteristics of rock
• color,
• streak,
• cleavage,
• luster,
• Hardness
• These characteristics are used to help identify a
rock.
8. • streak, (the colour of a mineral in its powdered
form. It is usually obtained by rubbing the
mineral on a hard, white surface, such as a tile
of unglazed porcelain, so as to yield a line, or
streak, of fine powder.)
• cleavage, (is a type of rock layering or planar
formation that forms within finely grained rocks
due to deformation and metamorphism caused
by heat and pressure.)
• luster, (describes how a mineral's surface
reflects light and how the interior of the mineral
may refract or bend light.)
10. What is stress in rock mechanics?
• Stress is the force exerted per unit area and strain is the physical
change that results in response to that force. When the applied
stress is greater than the internal strength of rock, strain results in
the form of deformation of the rock caused by the stress. Strain in
rocks can be represented as a change in rock volume and/or rock
shape, as well as fracturing the rock. There are three types of stress:
tensional, compressional, and shear.
11. Types of stress:
• Tensional stress involves forces
pulling in opposite directions,
which results in strain that
stretches and thins rock.
• Compressional stress involves
forces pushing together, and the
compressional strain shows up
as rock folding and thickening.
• Shear stress involves transverse
forces; the strain shows up as
opposing blocks or regions of the
material moving past each other.
12. How does rock mechanics connected
to Civil Engineering?
• Understanding the behaviour of rocks is
important in construction because it allows
engineers and contractors to design and build
structures that are appropriate for the specific
rock conditions at a given site, be it for civil or
mining purposes.
13. What is the use of rock mechanics in civil
engineering?
• Rock mechanics can help to predict how rocks
will respond to drilling, blasting and tunnel
and shaft boring, and can be used to design
safe and effective support systems for deep
excavations, open cuts, tunnels and
ventilation shafts.
14. Understanding the importance
of rock mechanics
Why would I need a rock mechanics engineer for my project?
A rock mechanics engineer is a specialised type of engineer who has
expertise in the mechanical behaviour of rocks and the design of
structures built on or in rock. If your project involves construction on or in
rock, a rock engineer can help to ensure that the project is designed and
built in a safe and effective manner. For example, a rock engineer can help
to evaluate the geologic conditions at the project site, identify potential
risks and hazards, and recommend appropriate design and construction
techniques to mitigate those risks. They can also provide expert advice on
the use of specialised equipment and techniques for drilling, blasting,
ripping, rock hammering, cutting and other rock-related operations. In
general, a rock engineer can help to ensure that your project is completed
successfully and safely, and that it is built to withstand the forces that will
act on it over time.
15. Understanding the importance
of rock mechanics
• Key industries
Rock mechanics is particularly important in mining and tunnelling.
In the mining industry, it is used to understand the behaviour of rocks in the
subsurface, and to design safe and efficient methods for excavating and
extracting minerals. For example,
rock mechanics can help to predict
how rocks will respond to drilling,
blasting and tunnel and shaft boring,
and can be used to design safe and
effective support systems for deep
excavations, open cuts, tunnels and
ventilation shafts.
16. Rock mechanics is particularly important in
mining and tunnelling.
• In tunnelling, rock mechanics is also critical for the design and construction
of tunnels and shafts. It is used to evaluate the geologic conditions along the
tunnel or shaft alignment, and
to determine the appropriate
excavation method, such as
drilling and blasting, tunnel
boring with tunnel boring
machines (TBM), road headers,
blind boring or raise boring and
support system for the specific
rock conditions. For example,
rock mechanics can help to predict the stability of the rock surrounding the
tunnel and can be used to design support systems that will prevent the tunnel
from collapsing or deforming.
17. Understanding the importance
of rock mechanics
What is rock mass classification?
Rock mass classification is a system that organises rock into
classes based on their characteristics. It provides a consistent
and standardised method for characterising the physical and
mechanical properties of rocks. This is important because the
strength and deformation behaviour of rocks can vary widely,
depending on factors such as their composition, structure,
and the geologic conditions under which they formed. By
classifying rock masses using a standardised system,
engineers and geologists can better predict the behaviour of
rocks and design structures that are appropriate for the
specific rock conditions at a given site.
18. Understanding the importance
of rock mechanics
How to assess rock characteristics?
• There are several ways that engineers can test the
characteristics of rocks. Common methods include:
Compression testing, Tension testing, and Indirect
testing.
19. Compression testing: This involves applying a compressive force to a rock
sample and measuring how much it deforms or fractures under the
applied force. This can provide information about the rock’s strength and
stiffness.
Tension testing: This involves applying a tensile force to a rock sample and
measuring how much it stretches or fractures under the applied force.
This can provide information about the rock’s ductility and toughness.
Indirect testing: In some cases, engineers may not have access to a rock
sample, or the sample may be too large to test directly. In these cases,
they can use indirect methods to estimate the rock’s characteristics. For
example, they may use borehole logs or geophysical surveys to infer the
rock’s composition and structure, or they may use statistical methods to
analyse the results of past rock-related projects to predict the behaviour
of the rock at a given site.
Overall, the specific methods used to test rock characteristics will depend
on the type of rock being tested, the available data, and the specific
engineering objectives of the project.
20. APPLICATIONS OF ROCKMCHANICS
• SURFACE STRUCTURES:
1. Low rise(Housing)
2. High Rise(Towers)
3. High Load(Hydro dams, Power Plants, Bridges)
• TRANSPROTATION ROUTES
1. Highways
2. Railways
3. Sewage Lines
4. Pipelines
• EXCAVATIONS
1. Quarries
2. Open pits
3. Strip mines
4. Trenches
5. Etc.
