The document discusses the behavior patterns of slopes and tunnels in discontinuous rock media, highlighting the influence of rock discontinuities on their mechanical response during excavation. It outlines tunnel types, geometry, geological factors affecting tunneling, and potential causes of tunnel failures. The conclusion emphasizes the need for thorough ground investigation to ensure safe and stable tunnel construction.

1. GLY 807
(ROCK MECHANICS)
BEHAVIOUR
PATTERNS OF
SLOPES TUNNELS
IN DISCONTINOUS
ROCK MEDIA

2. Presented By:
OMITOGUN SOLOMON T.
189078021
1st AUG.,2019

3. Outline
 Introduction
 Discontinuities in Rocks
 Description of Slopes Tunnels
 Types of Slopes Tunnels
 Tunnel Geometry
 Geological Conditions that influence Slopes
Tunnels excavation
 How Discontinuities in Rock Media Affects
Slopes Tunnels
 Factors to be considered in slopes tunnelling
 Causes of Failures of Slopes Tunnels in Rocks
 Conclusion

4. Introduction
 How rocks
mechanically
respond to
excavations,
especially in low
stress environments
as encountered in
slopes, are critically
affected by
discontinuities in the

5. Discontinuities in Rocks
 A discontinuity in rock is a plane or
surface that marks a change in
physical or chemical characteristics in
a soil or rock mass.
 Discontuinities in rocks affect their
shear strengths
 Discontinuities are either naturally
made or artificially induced.

6. Discontinuities in Rocks
Examples are:
 Bedding

7. Discontinuities in Rocks
 Foliation

8. Discontinuities in Rocks
 Cleavage

9. Discontinuities in Rocks
 Fracture

10. Discontinuities in Rocks
 Joint

11. Discontinuities in Rocks
 Fault plane

12. Discontinuities in Rocks
 Fold

13. Description of Tunnels
 Slope tunnels are tunnels constructed in steep
hills or mountainous areas, for economic and safe
operation .
 Tunnels are dug in types of materials varying from
soft clay to hard rock.
 Tunnel is an artificially constructed underground
passage to by- pass obstacles safely without
disturbing the over burden.
 Tunnels are created by the process of excavation.
 They are made into natural material (rocks)
 Empty inside
 Both ends are open to atmosphere
 Generally horizontal
 Thick walled structure looks like cylinder

14. Description of Tunnels

15. Description of
Tunnels(Contd.)

16. Types of Tunnels
There are three broad categories of
tunnels based on their purposes
 Mining ;
 Public works and
 Transportation.

17. Types of Tunnels
 Mining:
 Mine tunnels are
used during ore
extraction, enabling
labourers or
equipment to
access mineral and
metal deposits
deep inside
the subsurface.

18. Types of Tunnels(Contd.)
 Public works
tunnels carry
water, sewage or
gas lines across
great distances.
 The earliest
tunnels in Rome
for instance, were
used to transport
water to, and
sewage away
from, heavily
populated regions.

19. Types of Tunnels(Contd.)
 Transportation tunnel
 These are tunnels
created by the
excavations of rocks
to by-pass obstacles
safely without
disturbing the
overburden;
 They are underground
passage for road and
rail traffic.

20. Tunnel Geometry
 In the design of tunnels, designers attempt to
utilize a shape that will prove the most stable.
 Basic mechanics, in conjunction with the rock
mass classification, dictates the most effective
geometry.
 When tunnelling is strongly stratified rock, the
roof is often cut flat, taking advantage of the
rock's natural tendency to break along bedding
planes. By cutting the tunnel along bedding
planes and then supporting the roof, the tunnel
would be less apt to collapse than if a different
geometry were employed which cut across the
bedding of the rock, making it more unstable.

21. Tunnel Geometry(Contd.)
 The size is also very important. It is
generally considered that the
minimum size for a tunnel that will still
permit reasonable working space is at
least 7 feet (2.15 m) high by 4 feet
(1.2 m) wide, clear of the wall or the
supports, for a walkway. (Wahlstrom,
1973)
 The dimensional need to wider if it is
for vehicle/train traffic

22. Tunnel Geometry(Contd.)

23. Geological Conditions that influence
Slopes Tunnels excavation
1. Lithology
-Mineralogy
-Texture
-Structure of Rock

24. Geological Conditions that
influence Slopes Tunnels
excavation
2. Geological Structures
-Dip/Strike
-Folding
-Fault
-Joints

25. Geological Conditions that
influence Slopes Tunnels
excavation
3. Groundwater Condition
-Impervious formation
-Above water table
-Below water tabe

26. How Discontinuities in Rock Media
Affects Slopes Tunnels
 Effect of soil layers: Horizontal, vertical
and inclined layers have different kinds of
loading conditions for tunnels.

27. How Discontinuities in Rock
Media Affects Slopes Tunnels
Effect of faults:
Some problems in tunnelling are
caused by:
 The relation between the fault slope
direction and the tunnel direction
 Width of the fault zone
 The hydrostatic pressures in both
sides of the fault are some problems
in the tunnelling.

28. How Discontinuities in Rock
Media Affects Slopes Tunnels
Relation between the fault zone and the

29. How Discontinuities in Rock
Media Affects Slopes Tunnels
Tunnel excavations in the slopes:
 The discontinuities (layers, fissures)
inclined inside or outside of the slope
are very important regarding the
stress and strength of the tunnel.

30. How Discontinuities in Rock
Media Affects Slopes Tunnels
Tunnel excavations in the

31. How Discontinuities in Rock
Media Affects Slopes Tunnels
Effect of the folds:
 While tunnel is excavated in an area that
contains folded rocks, different stresses and
conditions may occur depending on the fold
type.
Fold axis and the tunnel direction is vertical
Fold axis and the tunnel direction is paral

32. Factors to be considered in slopes
tunnelling
 Tunnel dimensions,
 - Tunnel geometry
 - Length of tunnel,
 - Total volume to be excavated
 - Geological and rock mechanical
conditions
 - Ground water level and expected water
inflow
 - Vibration restrictions &
 - Allowed ground settlements

33. Causes of Failures of Slopes
Tunnels in Rocks
Tunnel collapse can happen for a number
of reasons such as:
 Inadequate ground investigation
 Shallow ground conditions
 Inadequate support measures
 Cost optimization
 Inexperienced contractors
 Inadequate supervision
 Delays of excavation and support erection.

34. Conclusion
 Excavation of tunnels in rock is a
complicated, dangerous, and
expensive process.
 Proper investigation should therefore
be carried out for proper tunnelling
process in discontinuous rock media;
thereby ensuring the excavation of a
safe and stable tunnel.

35. Thank You!