This document discusses hill road design and construction considerations. It covers hill road alignment selection, which considers river routes along valleys or ridge routes along mountain passes. Special geometric standards are needed for gradients and hairpin bends. Drainage structures and slope stability are also important due to terrain challenges. Retaining structures, river training, and landslide stabilization structures may be required as special hill road structures.

1. 5. Hill Roads

2. Topics As Per Syllabus
5.1 Introduction
5.2 Special Consideration in Hill Roads
5.2.1 Alignment of Hill Road Design: General Consideration, Route
Location in Hills, Gradient, Design and Types of Hair Pin Bends,
Different Types of Hill Road Cross-sections
5.3 Special Structures in Hill Roads
5.3.1 Types of Retaining Structures, River Training Structures, Landslide
Stabilization Structures and Gully Control Structures

3. 1. Introduction
• A hill road is usually defined on the basis of terrain.
• As per NRS the cross slope may be classified as:
• Road which passes through with a cross slope of 25% or more i.e.
mountainous or steep is termed as “Hill Road”.
• Hill road-one which passes through terrain with cross slope of 25% or more.
• There are sections along hill road with cross slope less than 25%, esp. when
the road follows river route.
• It is the overall terrain that must be considered.

4. Why Hill Road in Nepal?
• Nepal area = 140,000 sq. km approx.
• 66% covered with thinly/sparsely populated hills, mountains.
• 90% population reside in hilly areas and depends on agro products.
• Waterways, railways, airways - difficult
• Hilly Regions – Extremes of Climatic Conditions, Difficult and Hazardous Terrain,
Topography and Vast High Altitude Areas
• Challenges of Hilly Areas: Floods, Landslides, Snowfall, etc. – Fairly Weathered
Roads Possible
• But Hilly Areas Rich: in Natural Resources, Flora and Fauna – Important to launch
development Projects (e.g. Hydropower, etc.), tourism, etc.
• For Transport, Economy, Social Reasons – Justify the Construction of Hill Roads in
the Hilly Regions.
• Where Tunnels, Viaduct – Possible but Not Economical

5. 5.2 Special Consideration in Hill Roads

6. 5.2.1 Design and Construction Problems of Hill Roads
• Characterized by a highly broken relief with widely differing elevations and
steep slopes, deep gorges and several watercourses — unnecessarily
increase in road length
• Complex geology - different rock bed- geology differs from place to place –
assessment for road foundation is not easy
• Environmental impact - removal of vegetation etc. - stable slope may
change to unstable slope after road construction
• Great Variation in hydrological condition [ground water condition] vary
from place to place – may lead to damages after road construction
• New earth fill for road embankment may overload the relatively weak
underlying soil layer on hill slope – may trigger new and recurrent slides

7. • Requires installation of various types of special various road structures -
cost may rise upto 50 - 60% of total construction
• Steep slopes – high speed of surface runoff - provision of erosion
protection works
• Construction along relatively small approach stretches– different
construction technology may be needed
• Need of special safety precaution during construction
• Variations of climatic conditions - precipitation [rain and snow] , velocity of
wind etc. - need considerations
• Frequent blasting
• Design of hairpin bends to get heights

8. लमजुङ र मनाङ सीमामा पने मार्दीभीरको कच्ची बाटोमा र्दैननक उपभोग्य वस्तु पुर्याएर फक
ं र्दै यात्रुवाहक
नजपहरू । यनिखेर मनाङमा ५० वटा नजपले उपभोग्य वस्तु, स्थानीयवासी र पययटक ओसारररहेका छन्
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9. 5.2.2 Special Consideration in Hill Roads
1. Selection of Road Alignment
2. Special Geometric Standards (Gradient and Hari Pin Bends)
3. Cross-section Design
4. Design of Drainage Structures (Special Structures may Require)
5. Stability of Slopes

10. 1. Selection of Road Alignment
• Alignment through hilly areas is slightly different from aligning through a flat
terrain.
• For the purpose of efficient and safe operation of vehicles through a hilly
terrain special care should be taken while aligning the highway.
• Alignment should be - short, easy, economical & safe

11. • Alignment survey
• Reconnaissance-
• Tentative alignment after map study-topographical, geological and
meteorological
• Trace cut-
• route selected in step 1 is translated on the ground to provide an
access for subsequent detailed survey. A 1-1.2 m wide track is
constructed with easier gradient

12. • Detailed survey
• Fixing of bench marks
• Cross section and longitudinal sections – 15 m on straight, 30 m at sharp
curves
• Design of horizontal curves and hair pin bends
• Soil investigation, geology, hydrology study

13. 2. Special Geometric Standards
• The geometric standards followed in hilly areas are different from
those in at terrain.
• The alignment chosen should enable the ruling gradient to be
attained in minimum of the length, minimizing steep gradient, hairpin
bends and needless rise and fall.

14. 3. Cross-section Design

15. 4. Hill Side Drainage
• Adequate drainage facility should be provided across the road.
• Attempts should be made to align the roads in such a way where the
number of cross drainage structures required are minimum.
• This will reduce the construction cost.

16. 5. Stability of Slopes
• For hilly areas, the road should be aligned through the side of the hill that is
stable.
• The common problem with hilly areas is that of landslides.
• Excessive cutting and filling for road constructions give way to steepening of
slopes which in turn will affect the stability.

17. Factors Affecting Selection of Alignment in Mountainous and Hilly Areas
• Following points to be considered while aligning the hill roads:
i) Temperature
• The temperature of air varies inversely with altitude.
• The temperature drop being about 0.50C per 100m of rise.
• Similarly, the amount of heat received by hill slopes varies enormously with their orientation
in relation to the exposure to sun.
• Temperature - lower temperature in hill – drop by 0.5 0C per 100m rise - slopes facing south
and north
ii) Rainfall
• The amount of rainfall in hilly region is inversely proportional to the altitude.
• In hilly regions, wind often flows along the valley and gorges, as consequence of which the
rainfall in the valley is substantially higher than on high-lands and water-sheds.
• Also, maximum rainfall occurs in few months only. So these all uneven situation create the
problem in construction and maintenance of the road.
• Rainfall- heavy rainfall affects construction and maintenance

18. iii) Atmospheric pressure and Winds
• Atmospheric pressure is inversely proportional to altitude.
• At high altitudes, the velocity of wind is frequently coming at 25 – 30 m/s.
• The change in character of wind is due to appreciable difference of atmospheric pressure in
valleys and on mountain passes.
• Wind-high wind velocity contribute to damage –weathering of rocks, blowing away binding
material in valley
iv) Geological condition
• The tendency of sedimentary rocks is to slip under the influence of force parallel to the layer.
• The degree of stability of hill slopes depends upon the type of rock, the degree of strata
inclination or dip, the occurrence of clay seem, the hardness of rock and presence of ground
water.
• The instability of road may be due to ground water, landslides and unstable folds.
v) Route location
• The approach to the location of hill road alignment varies for the sections along the valley
bottom and along the mountain pass.
• The first is called ‘river route’ and second is called ‘ridge route’.

19. Route Location
• Hill road follow twist and turns- curves
• Location of alignment varies for sections along valley and mountain pass
• Alignment through valley - river route; mountain - ridge route
• A hill road may be only river route, ridge route or combination of both

20. River Route
• Most frequent Gentle slope
• Serves rural settlement situated next to
the water course
• Low vehicle operation cost
• Availability of construction material and
water
• Involves numerous horizontal curves,
construction of large bridges
• Special retaining protection on hill sides
• River training works may be extensive-
toe cutting, etc.
Ridge Route
• Steep gradient, sharp curves including hair pin
bends
• Expensive rock works, successive mountain
pass
• Route climbs up continuously from the valley
till mountain pass and descends down
• Construction of special structures, tunnels,
snow fences etc.
• Are most stable

21. a) River Route
• The location of a route along the river valley is known as river route. River
route is frequently used in hill road due to comparatively gentle gradient.
- It is advantageous that availability of water and other construction material
in vicinity.
- However, a river route may involve numerous horizontal curves,
construction of large bridges over tributaries and on stretches along steeply
sloping hill sides.
- It may also be necessary to construct special structures on hill side for the
safe of road against landslides.

22. b) Ridge Route
• A ridge route is characterized by very steep gradient, numerous sharp curves
including hair pin bends and the expensive rock works.
- The road usually follows the top section of the hill system and crosses
successively mountain pass.
- Geologically stable and comparatively mild slope sections are selected for the
artificial development of the route.