Joints play an important role in rock mechanics and geology. They influence rock mass classification systems like RQD, block size, RMR, and the Q-system. Joints also impact foundation strength, geohydrology, petroleum and mineral deposition, mechanical rock properties, mining feasibility, and toxic waste risk. Specifically, joints are factored into RQD, block size, RMR, and Q-system calculations. They also impart permeability that influences groundwater and fluid flow. Joint distributions control how ore-forming fluids circulate and where deposits form. Joints impact mechanical behavior and are an important consideration for engineering structures.

1. IMPORTANCE OF JOINTS
IN TERMS OF ROCK
MECHNICS
MRINALJYOTI ADHYAPOK

2. INTRODUCTION
• In geology, a joint is a fracture dividing rock into two sections that have not moved away from
each other. A joint sees little or no displacement.
• As Earth crust is full of joints, therefore their study and importance is very significance.
• joints are important not only in understanding the local and
regional geology and geomorphology, but also are important in development of natural
resources, the safe design of structures, and environmental protection. Joints have a profound
control on weathering and erosion of bedrock. As a result, they exert a strong control on how
topography and morphology of landscapes develop.

3. • Importance of joints in engineering and geological applications include:
1. In rock mass classification
2. foundation strength
3. Geohydrology/ Natural circulation of fluids
4. Petroleum and mineral deposition
5. Studying mechanical properties of rock masses
6. Mining and quarry operational feasibility
7. Toxic waste/ risk

4. 1. IN ROCK MASS CLASSIFICATION
a. In determination of RQD (Rock Quality Designation)
b. In determination of block size.
c. In determination of RMR (Rock Mass Rating)
d. In determination of rock quality ( Q system)

5. • In determination of RQD (Rock Quality Designation):
In many cases the degree of jointing is the most important factor for the stability of
rock masses. The volumetric joint count (Jv) is a simple measure of the degree of
jointing. It takes into account all the occurring joints and fractures and is easily
calculated from standard joint descriptions. The (Jv) has been used by engineering
geologists in Norway for several years and it has been a useful tool in the
description and classification of rock masses. The paper describes the procedure for
the calculation of the (Jv) and it shows how the joint spacings are included in the
measure.
RQD = 115 - 3.3 Jv.
Jv = Joint volumetric count

6. • In determination of block size:
Block size =
If 𝐽 𝑛 = 0, block size tends to infinite, it represents continuity i.e.
ground is made up of rock.
If 𝐽 𝑛 is more, ground is moving towards fractured ground.
Hence joints are very important parameter affecting geotechnical
behavior of ground.
𝑅𝑄𝐷
𝐽 𝑛

7. • In determination of RMR (Rock Mass Rating):
RMR is determined as an algebraic sum of six parameters given below:
1. Rock quality designation
2. Joint spacing
3. Joint condition
4. Joint orientation
5. Ground water condition
6. UCS of rock material.
RMR = RRQD + RJOINT SPACING + RJOINT CONDITION + RORIENTATION + RGROUND WATER CONDITION + RUCS
RMR Rock quality
0 - 20 Very Poor
21 - 40 Poor
41 - 60 Fair
61 - 80 Good
81 - 100 Very good

8. • In determination of rock quality ( Q system):
• The Q-system for rock mass classification is developed by Barton, Lien, and
Lunde. It expresses the quality of the rock mass in the so-called Q-value, on which
are based design and support recommendations for underground excavations.
• The Q-value is determined with
𝑹𝑸𝑫
𝑱 𝒏
represents block size
𝑱 𝒓
𝑱 𝒂
represents shear strength
𝑱 𝒓
𝑱 𝒂
represents condition or nature of rock
• Jw is the measure of water pressure which has an adverse effect on the shear
strength of joint due to reduction in effective normal stress.
𝑸 =
𝑹𝑸𝑫
𝑱 𝒏
×
𝑱 𝒓
𝑱 𝒂
×
𝑱 𝒘
𝑺𝑹𝑭

9. OTHER IMPORTANCE :
• Joints often impart a well-develop fracture-induced permeability to
bedrock. As a result, joints strongly influence, even control, the natural
circulation (geohydrology) of fluids.
• groundwater and pollutants within aquifers, petroleum in reservoirs,
and hydrothermal circulation at depth, within bedrock. Thus, joints are
important to the economic and safe development of petroleum,
hydrothermal, and groundwater resources and the subject of intensive
research relative to the development of these resources.

10. • Also, regional and local joint systems exert a very strong control on how ore-
forming (hydrothermal) fluids, consisting largely of H2O, CO2, and NaCl, that
formed most of Earth's ore deposits circulated within the Earth crust. As a result,
understanding their genesis, structure, chronology, and distribution is an important
part of finding and profitably developing ore deposits of various types.
• Finally, joints often form discontinuities that may have a large influence on the
mechanical behavior (strength, deformation, etc.) of soil and rock masses in, for
example, tunnel, foundation, or slope construction.
• As a result, joints are an important part of geotechnical engineering in practice and
research

11. THANK YOU