Unit:1 Introduction to Hill Roads Note( Hill Road)

Unit:1 Introduction to Hill Roads Note( Hill Road)

Unit:1_Introduction_to_Hil_ Roads_Note(_Hill_Road)

1.1 Definition and importance of hill roads in nepal    
Introduction

. A hill road may be defined as one that passes through a terrain with a cross slope of 25% or more.
. The roads constructed in mountainous regions of a country are known as hill roads or ghat roads.
. These roads present great difficulty in their alignment, design, construction, and maintenance.

 . Hence, a strong stable, and feasible road must be present in hilly areas for the overall development of other sectors as well.

Terrain Level or plain Rollin Mountainous Steep
Cross Slope(%) 0-10 10-25 25-60 >60

Importance of hill roads in Nepal

Why Hill Road in Nepal?
_ Nepal area 140,000 sq. km approx.
_ 66% covered with thinly/sparsely populated hills, and mountains.
_ 90% population resides in hilly areas and depends on agro products.
_ But Hilly Areas Rich: in Natural Resources Important to launch development Projects (e.g. Hydropower, etc.), tourism, etc.
_ Hilly Regions have Extremes of Climatic Conditions, Difficult and Hazardous terrain, Topography, and Vast High Altitude Areas.

Why Hill Road in Nepal?
Challenges of Hilly Areas: Floods, Landslides,Snowfall, etc. Fairly Weathered roads are possible
Waterways, railways, and airways are difficult
 Tunnels and viaducts are Possible but Not Economical
Transport, Economy, and Social Reasons justify the Construction of Hill Roads in the Hilly Regions.

1.2 Design and construction problems on hill roads

1.Characterized by a highly broken relief with Widely Differing Elevations and Steep Slopes, Deep Gorges, and Several Watercourses unnecessary increase in road length.

Unit:1_Introduction_to_Hil_ Roads_Note(_Hill_Road)

2.  Complex Geology Different Rock Bed     3. Geology differs from place to place

Unit:1_Introduction_to_Hil_ Roads_Note(_Hill_Road)

Unit:1_Introduction_to_Hil_ Roads_Note(_Hill_Road)
Unit:1_Introduction_to_Hil_ Roads_Note(_Hill_Road)

Unit:1_Introduction_to_Hil_ Roads_Note(_Hill_Road)

Unit:1_Introduction_to_Hil_ Roads_Note(_Hill_Road)


Unit:1_Introduction_to_Hil_ Roads_Note(_Hill_Road)


Unit:1_Introduction_to_Hil_ Roads_Note(_Hill_Road)

Unit:1_Introduction_to_Hil_ Roads_Note(_Hill_Road)

Unit:1_Introduction_to_Hil_ Roads_Note(_Hill_Road)
Unit:1_Introduction_to_Hil_ Roads_Note(_Hill_Road)

Unit:1_Introduction_to_Hil_ Roads_Note(_Hill_Road)

1.3 Special Consideration in Hill Roads

       1. Selection of Road Alignment
2.SpecialGeometricStandards (Gradient and Hari Pin Bends)
3.Cross-section Design
4.Design of Drainage structures (special structures may be required)
5. Stability of Slopes

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.

➢ Aim of Hill Roads: Alignment should be – short, easy, economical & safe, line of communication between the obligatory points considering the physical features of the region and traffic needs as well as the least disturbance to the eco-system

➢ Ideal Road Alignment: one which will cause the least overall transportation cost taking into account the costs of construction, maintenance, and recurring cost of vehicle operation

2. Geometric Standards

➢ Geometric standards followed in hilly areas are different from those in plain terrain.Unit 2: Hill Road Alignment Note (Hill Road)

➢ Roads in the hilly areas require special attention in fixing up the standards for geometric design because of various factors: types of vehicles using the roads, total daily tonnage, difficulty in construction, type of surface to be provided, topography of the area, etc.

➢ The alignment chosen should enable the ruling gradient to be attained at a minimum of the length, minimizing steep gradient, hairpin bends, and needless rise and fall. 

➢ Geometric features of a highway except crosssectional elements do not lend to stage construction.

➢Improvement of features like grade and curvature at a later date can be very expensive and sometimes impossible.

➢ It is therefore necessary that the ultimate geometric requirements of hill roads are in view right in the beginning.

3. Cross-section Design

Cross section of a road in hilly terrain is determined by:

➢  The original ground slope of the site,
➢  The slope of the road formation,
➢  width of roadway,
➢  side drain size and
➢  shape and so on

Unit:1_Introduction_to_Hil_ Roads_Note(_Hill_Road)

 Various Configurations of Hill Road Cross Sections

       1.Cut and fill
2.Bench type
3.Box cutting
4.Embankment with retaining walls
5.Semi bridge
6. Semi tunnel
7. Platforms

1) Cut and Fill

_ With a hill side slope of over 2%, a cut and fill road bed is the cheaper and environment friendly type of construction.

_  The fill mass is obtained from the cut material at the same location or within free haul distance.

_ To ensure adequate stability of embankment, benches are made on the surface of the hill side with a height of 0.5 m and a length varying 1.5 m to 3.0 m depending on the slope.

_ The settlement of the fill portion of road bed sometimes causes the appearance of longitudinal cracks in the pavement.

_ That is why it is recommended to locate roads on stable hills cross slope exceeding 1 in 3 entirely in a cutting at the higher cost of making full bench.

_ Roads with hard and costly pavement structures are to be preferably located in the full bench while those with low-cost surface (WBM, gravel, earthen) be made with cut and fill road bed.

Unit:1_Introduction_to_Hil_ Roads_Note(_Hill_Road)

  2) Bench Type

A cross-section of the bench type although entailing some increase in earthwork ensures the complete stability of the roadbed, if hillside itself is stable

Unit:1_Introduction_to_Hil_ Roads_Note(_Hill_Road)

 3) Box Cutting

_  When the location of the roadbed is unstable or unstable along the hill side due to one or another reasons, the roadbed is designed as a trench type of cross-section.

_ This type of roadbed increases earthwork to a large extent.

_  It is introduced in order to meet the geometric design standards for a given category of road.                         

                           
Unit:1_Introduction_to_Hil_ Roads_Note(_Hill_Road)

_ When a road is ascending up the grade is reduced substantially by raising the formation line at the beginning with fill and lowering the same at the following section with box cutting.

 4 ) Embankment with Retaining Walls

_ On steep slopes over 30-35 degrees, the earthwork involved in constructing the embankment slope line meets the natural ground line at an acute angle far away from the center line of the road.

_ In the first case of retaining wall is provided to reduce the cost of earthwork and to increase the stability of embankment.

_ When the original ground slope is steeper than the embankment slope these two slope lines never meet down hill.

_ In the second case retaining walls are necessary to support the embankment soil on steep ground at the edge of the road itself.

_ An embankment with a retaining wall has greater stability and should be preferred.

Unit:1_Introduction_to_Hil_ Roads_Note(_Hill_Road)

_ Retaining walls are also constructed on a less steep ground slope to increase the stability of the roadbed.

5) Semi Bridge

_ If the road is located across a steep hill slope retaining wall may have to be of substantial height.

_ In such cases, in order to reduce the quantities of work, a roadbed with a semi-bridge type of structure may be constructed.

_ Part of the roadway is accommodated on a bench cut and part on the semi bridge.

Unit:1_Introduction_to_Hil_ Roads_Note(_Hill_Road)

6) Semi Tunnel

_ When cutting into steep hills in stable rock faces the rock may be permitted to overhang the road, reducing rock works. Such a cross-section is called a semi-tunnel.

_ Road in-half tunneling is advantageous for high-altitude hill roads as they do not get blocked by snow.

Unit:1_Introduction_to_Hil_ Roads_Note(_Hill_Road)

7) Platform

_ On the precipitous/very steep slopes, where shifting the route into the hillside will lead to enormous rock work, which would substantially increase the cost of road construction, and where semi tunnel cannot be constructed due to the geological condition, platforms are usually cantilevered out of the rock on which roadway is partially located.

_ When the cross slope of the hill is very small, the road may be in full embankment.

Unit:1_Introduction_to_Hil_ Roads_Note(_Hill_Road)

_ Filling may be small or heavy.

_ In case of heavy filling, retaining walls should be constructed on both side of the formation.

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 is minimum.

1) Drainage of water from hills slopes

Surface water flowing from the hill slop towards the roadway is one of the main problems in drainage of hill roads.

- It is describe that the water from the hill side is not allowed to flow into the side drains due to the problems maintaining the side drains intended for water from roadway.

Unit:1_Introduction_to_Hil_ Roads_Note(_Hill_Road)

- In order to intercept and divert the water form hill slope catch water drains are provided and then it is diverted by side drain.

2) Road -Side drains

Side drain is provided only on the hill side of the roads and not on the both sides. Due to limitation of in the formation width, the side drains are constructed to such a shape that at emergency the vehicles could utilize the space for crossing at low speed or for parking.

3) Cross drainage 

As far as possible ,cross drainages should be taken under the road and  at right angle to it .

- At the head of small cross drains catch pits must be provide to collect the stones and rubbish and to prevent scour.

- In hill roads where rainfall is heavy, it is recommended that culverts should be provided every 60 to 90m, to facilitate drainage of water cross the roads.

4) Sub-surface drainage

The seepage flow of water on hill roads is one of the major problems during and after the monsoons.

- The seepage flow causes problems of slopes stability as well as weakening of the road bed and pavement.

- The seepage flow is controlled by suitable sub-surface drainage system i.e by longitudinal pipe drain,by controlling of capillary rise,by lowering the water table.

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 the steepening of slopes which in turn will affect the stability.
   

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