5.Hill Roads 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 esp. • Hill road-one which passes through terrain with cross slope of 25% or more. mountainous or steep is termed as “Hill Road”. • It is the overall terrain that must be considered. when the road follows river route. . Introduction • A hill road is usually defined on the basis of terrain.e.1. • There are sections along hill road with cross slope less than 25%. • As per NRS the cross slope may be classified as: • Road which passes through with a cross slope of 25% or more i. 000 sq. etc. • 66% covered with thinly/sparsely populated hills. Viaduct – Possible but Not Economical . • Waterways. Flora and Fauna – Important to launch development Projects (e. railways.Why Hill Road in Nepal? • Nepal area = 140. etc. Hydropower. • 90% population reside in hilly areas and depends on agro products. km approx. Social Reasons – Justify the Construction of Hill Roads in the Hilly Regions. tourism. Landslides. Topography and Vast High Altitude Areas • Challenges of Hilly Areas: Floods. Snowfall.). Difficult and Hazardous Terrain. Economy. – Fairly Weathered Roads Possible • But Hilly Areas Rich: in Natural Resources. airways .g.difficult • Hilly Regions – Extremes of Climatic Conditions. • For Transport. etc. mountains. • Where Tunnels. 2 Special Consideration in Hill Roads .5. deep gorges and several watercourses — unnecessarily increase in road length • Complex geology .5. .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 .1 Design and Construction Problems of Hill Roads • Characterized by a highly broken relief with widely differing elevations and steep slopes.geology differs from place to place – assessment for road foundation is not easy • Environmental impact .removal of vegetation etc.2.different rock bed. • Requires installation of various types of special various road structures .precipitation [rain and snow] .need considerations • Frequent blasting • Design of hairpin bends to get heights .60% of total construction • Steep slopes – high speed of surface runoff . . velocity of wind etc.cost may rise upto 50 .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 . लमजजङ र मननाङ ससीमनामना पनर्ने मनारर्दीभसीरकको कच्चसी बनाटकोमना रदैननक उपभकोग्य वस्तज पजरयनाएर फकर्कंरदै यनाततरुवनाहक नजपहरू । यनतखखेर मननाङमना ५० वटना नजपलखे उपभकोग्य वस्तज. स्थनानसीयवनाससी र पयर्यटक ओसनानररहखेकना छनत http://bit.ly/1P8Nrd2 . Selection of Road Alignment 2. Special Geometric Standards (Gradient and Hari Pin Bends) 3. Cross-section Design 4.5.2 Special Consideration in Hill Roads 1. Design of Drainage Structures (Special Structures may Require) 5.2. Stability of Slopes . easy. • For the purpose of efficient and safe operation of vehicles through a hilly terrain special care should be taken while aligning the highway.short. economical & safe . • Alignment should be . Selection of Road Alignment • Alignment through hilly areas is slightly different from aligning through a flat terrain.1. 2 m wide track is constructed with easier gradient . geological and meteorological • Trace cut• route selected in step 1 is translated on the ground to provide an access for subsequent detailed survey.• Alignment survey • Reconnaissance• Tentative alignment after map study-topographical. A 11. 30 m at sharp curves • Design of horizontal curves and hair pin bends • Soil investigation. hydrology study . geology.• Detailed survey • Fixing of bench marks • Cross section and longitudinal sections – 15 m on straight. minimizing steep gradient. • The alignment chosen should enable the ruling gradient to be attained in minimum of the length. hairpin bends and needless rise and fall.2. Special Geometric Standards • The geometric standards followed in hilly areas are different from those in at terrain. . Cross-section Design .3. 4. Hill Side Drainage • Adequate drainage facility should be provided across the road. • This will reduce the construction cost. . • Attempts should be made to align the roads in such a way where the number of cross drainage structures required are minimum. the road should be aligned through the side of the hill that is stable. . • The common problem with hilly areas is that of landslides. Stability of Slopes • For hilly areas.5. • Excessive cutting and filling for road constructions give way to steepening of slopes which in turn will affect the stability. slopes facing south and north ii) Rainfall •) The amount of rainfall in hilly region is inversely proportional to the altitude.5 0C per 100m of rise. •) Also. •) Temperature .heavy rainfall affects construction and maintenance . •) The temperature drop being about 0.lower temperature in hill – drop by 0. wind often flows along the valley and gorges.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. maximum rainfall occurs in few months only. So these all uneven situation create the problem in construction and maintenance of the road. the amount of heat received by hill slopes varies enormously with their orientation in relation to the exposure to sun. •) Rainfall. •) In hilly regions. •) Similarly.5 0C per 100m rise . as consequence of which the rainfall in the valley is substantially higher than on high-lands and water-sheds. iii) Atmospheric pressure and Winds • Atmospheric pressure is inversely proportional to altitude. 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. • Wind-high wind velocity contribute to damage –weathering of rocks. • At high altitudes. •)The first is called ‘river route’ and second is called ‘ridge route’. • The instability of road may be due to ground water. the occurrence of clay seem. the degree of strata inclination or dip. landslides and unstable folds. the hardness of rock and presence of ground water. • The change in character of wind is due to appreciable difference of atmospheric pressure in valleys and on mountain passes. 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 velocity of wind is frequently coming at 25 – 30 m/s. . • The degree of stability of hill slopes depends upon the type of rock. river route.ridge route • A hill road may be only river route. mountain . ridge route or combination of both .curves • Location of alignment varies for sections along valley and mountain pass • Alignment through valley .Route Location • Hill road follow twist and turns. toe cutting. bridges • Special retaining protection on hill sides • River training works may be extensive. • Are most stable . etc. tunnels. construction of large • Construction of special structures. sharp curves including hair pin bends • • Availability of material and water construction Expensive rock works. snow fences etc. successive mountain pass • Route climbs up continuously from the valley till mountain pass and descends down • Involves numerous horizontal curves.• Most frequent Gentle slope River Route situated • Serves rural settlement next to the water course • Low vehicle operation cost Ridge Route • Steep gradient. .It is advantageous that availability of water and other construction material in vicinity. . .a) River Route • The location of a route along the river valley is known as river route.However. . a river route may involve numerous horizontal curves.It may also be necessary to construct special structures on hill side for the safe of road against landslides. construction of large bridges over tributaries and on stretches along steeply sloping hill sides. River route is frequently used in hill road due to comparatively gentle gradient. b) Ridge Route • A ridge route is characterized by very steep gradient. . numerous sharp curves including hair pin bends and the expensive rock works. .Geologically stable and comparatively mild slope sections are selected for the artificial development of the route.The road usually follows the top section of the hill system and crosses successively mountain pass. .