The document discusses the significance of geological investigations in highway engineering, covering critical topics like design principles, road grades, location surveys, and environmental considerations. It outlines methods for reconnaissance, the importance of engineering, environmental, social, and economic data in planning, as well as the effects of water on civil engineering projects. Key aspects also include the finalization of highway routes and geological factors influencing construction and foundation stability.

1. GEOLOGICAL INVESTIGATIONS FOR
HIGHWAYS
by
Prof. A. Balasubramanian
Centre for Advanced Studies in Earth Science
University of Mysore, India

2. Introduction:
Highway engineering is an engineering discipline
branching out from civil engineering.
This subject involves the planning, design,
construction, operation, and maintenance of roads,
bridges, and tunnels to ensure safe and effective
transportation of people and goods.

3. Highway engineers must take into account of the
future traffic flows, design of highway
intersections/ interchanges, geometric alignment
and design, highway pavement materials and
design, structural design of pavement thickness,
and pavement maintenance.
Design:
The most appropriate location, alignment, and
shape of a highway are selected during the design
stage.

4. Grade:
The term "grade" is used in several different ways
with respect to roads and highways.
"Grading" a road means to smooth out the roadbed
with earthmoving equipment during the
construction phase. The grade of a road is defined
as a measure of the road's steepness as it rises and
falls along its route. In other words, it is the
magnitude of its incline or slope.

5. The term "sub-grade" lies beneath a roadway and
is used as a supporting base.
Highway grades are usually expressed as a
percentage.
Any number represented in decimal form can be
converted to a percentage by multiplying that
number by 100.
When a new highway is being planned, its grade
over its various sections is one of the key aspects
that must be determined in advance.

6. The grade of the road is very important for the
safety of the motorists, who will be using it.
Advantages
Roads with grade separation generally allow traffic
to move freely, with fewer interruptions, and at
higher overall speeds;
this is why speed limits are typically higher for
grade-separated roads.

7. Design Controls:
The geometric design of roads is the branch
of highway engineering concerned with the
positioning of the physical elements of the
roadway according to standards and constraints.
The basic objectives in geometric design are to
optimize efficiency and safety while minimizing
cost and environmental damage.

8. Profile:
The profile of a road consists of road slopes, called
grades, connected by parabolic vertical curves.
Vertical curves are used to provide a gradual
change from one road slope to another, so that
vehicles may smoothly navigate grade changes as
they travel.

9. Level terrain: Any combination of grades and
horizontal and vertical alignment permitting
heavy vehicles to maintain approximately the same
speed as passenger cars. Grades are generally
limited to 1 or 2 percent.
Rolling terrain: Any combination of grades and
horizontal and vertical alignment causing heavy
vehicles to reduce their speeds substantially below
those of passenger cars, but not to operate at crawl
speeds.

10. Hilly terrain: Any combination of grades and
horizontal and vertical alignment causing heavy
vehicles to operate at crawl speed.
Location Surveys for Highway:
The aim of location survey is to select a route.
Resulting Route:
After comparison of the different alternative
design, the route is selected which has cheapest
overall cost, considering capital investment,
maintenance, expense and saving to the road user.

11. The highway location and design process:
Desk Top study of the area:
The possible desk study for highway of an area
include;
Maps, Aerial photographs, charts or graphs to
obtains, engineering data, environmental data,
social data, economic data.
Engineering data:
All details of the topography, soil and problems
like drainage and maintenance.

12. These should be investigated before a scientific
plan programmed can be suggested.
The engineering data includes following things;
Topographic and geological maps.
Stream and drainage basin maps.
Climatic records.
Preliminary survey maps of previous projects.
Traffic surveys and capacity studies.
Environmental data:
The environmental data required for desk study of
area includes;

13. Agricultural soil surveys indicating soil erodibility.
Air pollution studies.
Noise and noise attenuation studies.
Fish and wild life inventories.
Historical studies.
Social data:
The social data obtained may be analyzed for
future trends in development of an area.
It includes;
Demographic and land use information.
Census data.

14. Zoning plans and trends.
Building permit records, motor vehicle registration
records.
Living standards of locality.
Economic data:
The economic data is essential to study the various
financial aspects like source of income and manner
in which funds for project may be mobilized.
It includes;
Overall cost of previous projects.

15. Unit construction costs data.
Agricultural, economical and industrial data etc.
Reconnaissance survey for highway location:
Two methods;
Conventional ground method.
Aerial photography.
Conventional ground method:
In this method a field survey party inspects a fairly
broad stretch of land along the proposed
alternative routes of the map in the field.

16. Intensive reconnaissance is very important for
highway location in a new country as well as
where completes abandonment and replacement of
an existing road are planned.
The various steps of reconnaissance for highway
location in a rural area are;
Initially help is taken from already available maps,
particularly topographic maps of the area so that
most promising general route may be laid out for
careful inspection on the ground.

17. Once a route selected on the map by crude but
rapid survey method, a survey is made along the
path selected on the map.
Cost factors such as favorable and unfavorable soil
conditions, the number and sizes of structures, the
amount of excavation and embankment, alignment
and grade.
Possible alignment:
In mountainous country with well defined summit
ranges, there is usually a suitable pass along the
drainage on both sides.

18. The least expensive and frequently the straightest
line may lie just above high water in streams often;
however, the rise of valley may exceed the
maximum permissible grade.
At times a more favorable location lies on the
hillside at some height above the stream.
Mountain location:
On occasion, the route must climb from stream
level to an adjoining pass or summit.
The road must be long enough to provide for the
required gain in elevation at max permissible rate.

19. Depending sooner from the level valley will result
in climbing to summit in less grade and moderate
curvature.
Excessive use of switch backs should be avoided.
In snow location:
In sow areas locations should be confined to slopes
exposed to the sun in order to avoid icing on the
roadway and ease snow removal problems.
Reconnaissance report:
This report must consist of;
Total length of line.

20. The elevation of main and intermediate summit.
All adverse grades.
Stream crossing.
Nature of construction.
Right of way circumstances.
Soil conditions.
Unusual or troublesome condition.
Approximate estimate of cost.

21. Preliminary location survey:
After the preferred location has been established,
the preliminary location survey serves as basis for
fixing the actual highway location.
Elevations - At 100ft and at breaks in the ground
provide data for profile and serve as starting point
for cross-sections that covers a strip of land on
each side of P-line.
Cross-section - are of width 100’ to 800’,
depending upon;Standard of accuracy, Speed of
work and instrument used.

22. Final location survey:
Final location is essentially fixing of the details of
the projected highway.
It serves the dual purpose of Permanently
establishing the center line.
Collecting information necessary for preparation
of plans for construction.
The line should be established as closely as is
practical to the line drawn on the preliminary map.

23. It should conform the major and minor control
points and the alignment that was previously
determined.
The final location survey is complete when all
necessary information in available and ready for
designer to use.
It in insured that all information required
preparation of complete construction.
All information pertaining to:
Alignment,
Topography,

24. Bench mark levels,
Cross sections,
Section corner ties and other land ties,
Drainage and utilities.
Geological Aspects and Investigations:
(i) Structures in which the basic problem is
concerned with the foundation only
e.g. tall buildings, bridges, long walls, etc.

25. (ii) Structures which are constructed in and from
the earth i.e. fills e.g. under-fills and back-fills of
the highways, motorways, railways, tunnels,
bridges, culverts, dams & reservoirs, retaining
walls, etc.
(iii) Structures which are concerned with the
stability of earth slopes
e.g. embankments, mounds, levees, etc.

26. (iv) Structures which are concerned with water-
tightness problems – where the geology of water-
tightness of the site is involved
e.g. rivers, lakes, canals, reservoirs, catchment-
areas, etc.
(v) Projects concerned with Ground-water and
Hydro-geology.
e.g. accessories of dams, reservoirs, rivers, canals,
drains and foundations of the bridges.

27. Effects of water on the site and foundation of a
civil engineering project:
Special consideration is given to the effects of
surface-water and of a big channel or source of
water existing near a proposed Civil Engineering
Project and effects of the sub-surface water in and
under its foundation that is likely to affect the
project in the future.

28. Water reduces the Load Bearing Capacity of the
foundation of a Civil Engineering Project and
causes the deterioration of the cement and concrete
structures too.
Projects existing in or close to the water e.g.
accessories of dams, reservoirs, rivers, canals and
foundations of the bridges as well as the projects to
be laid on and inside the ground that is likely to be
affected with the water during the heavy rains.
Examples are:

29. highway, motorway,
railway, runway,
tunnel, foundations, etc
are designed against the worst and aggressive
condition of the water i.e. against the heavy rains,
rainy season, floods, etc likely to exist around and
under a Civil Engineering Structure in the future.