This lesson is about engineering geology

1. ROADS AND HIGHWAYS
BY: ISMAIL M. ALI

2. Introduction
• Roads and highways are always very important
projects for any country and an index of its
development. Their planning, designing,
construction and maintenance are among the
major duties of civil engineers the world over.
As with any other civil engineering project,
geological investigations play important role in
the design, stability and economical
construction and maintenance of the roads.

3. road describes lesser traveled way

4. Highway refers to a major traveled way

5. Geological investigation
Topography
• Topography or the landform of a region is
single most important factor that controls
the selection of alignment of a road project.
Topographic maps would reveal the
existence of various land features like valleys
and the inflowing streams, the hills and their
undulations, the plateaus and the plains with
all their varying configuration from place to
place.

6. Lithological Character
Geological surveys should invariably provide
all possible details regarding the composition,
texture, structure and origin of rocks and
sediments making the ground through which
the proposed alignment of the highways has
to pass.

7. Geological Structures
• Such structural features include:
• (a) Dip and strike,
• (b) Joints,
• (c) Fault planes.

8. • (a) Dip and Strike:
(i) Cut is Parallel to the Dip Direction:
• In such a case the risk of failure is minimal.
(ii) Cut is made Parallel to the Strike:
• In such case the road cut is considered quit
stable.

10. (b) Joints:
• In major road construction programmes,
therefore, jointed rocks have to be provided
artificial support by breast walls and retaining
walls for ensuring stability.

11. (c) Faults:
• Faulting generally leads to the crushing of the
rock along the fault planes and shear zones.
Such a condition is, of course, very
unfavorable for a cut when it happens to form
upper or lower slope or even base of the cut.
It worst type of planes of potential failure.

12. Weathering
• In some cases, when the strata along or under
a cut is composed of layers of rocks of
different hardness, the softer layers get
weathered at a faster rate than the overlying
or underlying harder rocks. This generally
results in undermining which might cause slips
or falls of the whole face.

13. • Sometimes, when the top layers are
weathered too heavily, the slope might
experience a persistent rock fall or debris-fall
type of situation from above.

14. Groundwater Conditions
• It is quite likely that a water bearing zone
(aquifer) might be intersecting the base or
slopes of an alignment. Specific care and
design would be required for these natural
water conduits. These are always to be taken
as weak and hazardous zones in the road.

15. Complicated Regions for Roads
A. Roads in Hilly Regions:
Aerial Survey:
• Similarly, another very important complication
is the area that has to be surveyed in the
specified time. This will require, obviously, use
of some quicker methods of surveying. Hence
aerial surveying may become necessary for
successful completion of the project in
specified time.

16. Meandering:
• In fact, the topographic and the permissible
factors necessitate, more than often a
meandering, zig-zag course.

17. • b. Roads in Marshy Regions:
• In all such regions, the most satisfactory
method for ensuring stability is to excavate
the weak soil or peat or other such material
and replace it with sound material. This is,
obviously, possible when the area involved is
quite small and the deposit is shallow in
character.

18. • c. Roads in Water Logged Areas:
• There are two possible ways to treat this
trouble:
• (i) Lower down the water-table to the safe
limits;
• (ii) Increase the thickness of the road crust.

19. • d. Roads in Permafrost Regions:
• Vegetation, if any, should not be disturbed
and a well-planned ‘insulating layer’ should be
given in between the warm fill of the road
surface and the ice below. Ice crystals should
be allowed to remain in their original state.

20. THANK YOU