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Introduction of Drainage and Hill (Mountain) Roads

Introduction

  • Roads constructed in mountains region is  called hill roads.
  • There are different considerations while designing hill roads as compare to plain area roads.
  • Types of curve used in hill roads is of different than plain road.
  • All geometric parameters will gets changes while designing hill roads such as- Curves, Super elevation, SSD, OSD, Extra Widening, etc.

Components parts of Hill Roads

  1. Road Bed
  2. Side Drain
  3. Parapet Drain
  4. Catch Water Drains
  5. Brest Wall
  6. Retaining Wall
  7. Cross Drains

Road Bed

  • The pavement potion of hill road is called road bed.
  • Function: To resist stresses developed due to moving traffic.

Side Drain

  • Drain provided on the sides of road is called side drain.
  • Side drains runs parallel to the length of road.
  • Function: To collect and drain off rain water collected from camber of road.

Parapet Wall

  • Wall which is provided above the formation level in the down side slope is called parapet well.
  • Function: Protection to the traffic against falling down the hill slope.

Catch Water drain

  • It is drain provided on higher slope running parallel to the length of road.
  • Function: To make intercept for runoff coming from top of hill and divert water in to near by cross drains.

Brest Wall

  • The wall constructed to up side slope is called retaining wall.
  • Function: Protect road from sliding of up side slope.

Retaining Wall

  • The wall constructed to down side slope of road is called retaining wall.
  • Function: To protect down slope from sliding.

Cross Drains

  • The drains which is laid along width of road is called cross drains.
  • Function: to drain off rain water collected in side drains and catch drains.

Factors Controlling Alignment of Hill Road

Length of Road

  • Alignment of road should be short as possible because cost will be increased as length of road increases.

Geometrical Standards

  • Alignment of road should have proper geometrical standards such as Gradient, Curves, SD, Radius of curves.
  • Minimum radius of curve for hill road is allowed to 50m.

Existing Saddle or Pass

  • Alignment of road should not pass through ridge line of hill to avoid extra cutting and filling.
  • Alignment should passes through series of  hills through existing saddle points.

Drainage Line

  • Alignment of road should be parallel to drainage line to avoid no of cross drainage drains.

Stability

  • Alignment of road should passes along the stable and side having mild slope of hill road.

Altitude

  • Altitude of road should not be passes through high altitudes will increase no. of cross drains.
  • High altitude causes problem of snow falling and low altitude will increase no. of cross drains.
  • Alignment of road passes through altitude between 900 to 1500m.
  • Alignment of road should faces sun and not located in windward side of hill.

Cutting Through Rocks Alignment of road should not passes through solid rocks to avoid cost of cutting.

Alignment Survey of Hill Road

Alignment of Hill Roads is fixed in three stages:

  1. Reconnaissance
  2. Trace Out
  3. Detailed Survey

Reconnaissance

  • The temporary alignment of road is fixed during reconnaissance survey by studying topographical, geographical and metrological maps of the area.
  • Arial survey is carried out for remote area.

Trace Out

  • The route selected during reconnaissance survey is translated on ground so as to collect details from actual site.
  • 1 to 1.5m wide track is constructed so as to collect details.

Detailed Survey

  • During detailed survey BM are mixed on ground.
  • Prepare c/s along length and along width.
  • Mark the centre line and boundary line of highway.
  • Hydrological and soil investigation is carried out.

Construction Procedure of Hill Road

  • Rock Cutting
  • Vertical Cutting
  • Retaining Wall
  • Foundation of Retaining Wall
  • Revetment Wall
  • Pavement Construction

Types of Hill Roads Curves

There are main three types of curves used in hill road curves.

  1. Hair Pin Curve: The curve of hill road which changes its direction through 180o.
  2. Salient Curves: Curve having their convexity on the outer edge of hill road.
  3. Re-entrant Curves: Curve having convexity on the inner edge of hill road.

Formation of Hill Road

Formation of hill road done in following situation:

  1. Wholly in Cutting: Formation width of pavement of hill road is constructed fully in cutting.
  2. Partially in Cutting and Partially in embankment: Formation width of hill road is constructed partly in cutting and partly in embankment.
  3. Wholly in embankment: Formation width of hill road constructed fully in filling (embankment).

Landslide

The downward movement of soil mass or rock along the slope due to gravity is called landslide.

Types of Landslide

  1. Free Fall Landslide: When there is free fall or rolling of rocks and soil mass along the slope then it is called free fall landslide.
  2. Toppled Landslide: Topples are nothing but overturning or forward rotation of rock bed along slope.
  3. Slide Landslide: The downward movement of soil mass or rock along failure plane of downward slope.
  4. Complex Landslide: When there is combined effect of two or more landslide then it is called as complex landslide.

Causes of Landslide

1. Natural Causes of landslide

  • Climate-Heavy Rainfall
  • Geology and Topography
  • Earthquake
  • Weathering of Rock
  • Erosion of Soil and Rock
  • Volcanos
  • Forest Fires

2. Human causes of Landslides

  • Mining
  • Blasting
  • Increase in traffic load

Effect of landslide

  • Lead to economic declination or loss
  • Damage of infrastructure
  • Loss of life
  • Affects beauty of landscapes
  • Impact on river ecosystem

Prevention of Landslide

  • Provide benching on side slope.
  • By providing proper drainage system.
  • By constructing retaining wall and breast wall.
  • By soil stabilization techniques.
  • By cement grouting or concrete lining.
  • By rock nailing.
  • By increasing vegetation on side slope.
  • By fixing geosynthetic net on sloping side.

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