Basic Components of Road Structure | Flexible Pavements | Road Pavement Layers | Method of Road Construction
In this Article today we will talk about the Basic Components of road | Road Structure | Components of Flexible Pavements | Road Pavement Layers | Road Construction Layers | Method of Road Construction
What are the Components of Road structure?
In this article will study about components of the roads and the structure of the roads and its composition after reading this article you will understand a lot about components of the road structures. We will try to make it as simple it can be.
1. Sub Grade:
Subgrade is the foundation of the road, thus its the lowest and most important component of road structure. components of Flexible Pavements
- If natural surface is above the formation level then the surface is cut down to proposed sub grade surface
- If natural surface is below the formation level then the sub grade will be above the ground level Road Pavement Layers
- It should be constructed at least 60 cm (2ft) high from highest flood level of the area
Function of Sub grade:
- Bears all the load thus acts as a foundation of road
- Transfer load through grain to grain contact
Material of sub grade should be strong enough to bear the loads, easily accessible and available in the vicinity and cheap.
2. Sub Base:
- Upper Base Course
- Sub or Lower Base Course
- Constructed above the sub grade
- Not needed if the sub grade is of very high strength
- In case of flexible pavement upper and lower base courses are separated having different materials
- In case of rigid pavement only upper base course is provided
- Thickness varies from 7.5 (3in) to 15cm (6in)
Functions of sub base:
- Prevent rise of water or capillary action
- Should be better than the material of Sub Grade
- The Upper Base Course is made up of sand, gravel, and stone
- The Lower Base Course is made up of cheaply available material i-e rock and stone fragments Method of Road Construction
3. Road Base:
Due to quality of material used in the road base it is divided into
- Upper Road Base
- Lower Road Base
- Constructed above the Sub Base
Functions of Road Base:
- To avoid the distortion of wearing course due to its sufficient density
- Supports the wearing course
- In case of Upper Road Base the material is of high quality as the load intensity is high
- In case of Lower Road Base the material is of high quality as the load intensity decreases Method of Road Construction
4. Surface course
Surface course is the layer directly in contact with traffic loads and generally contains superior quality materials. They are usually constructed with dense graded asphalt concrete(AC). The functions and requirements of this layer are:
- It provides characteristics such as friction, smoothness, drainage, etc. Also it will prevent the entrance of excessive quantities of surface water into the underlying base, sub-base and sub-grade,
- It must be tough to resist the distortion under traffic and provide a smooth and skid- resistant riding surface,
- It must be water proof to protect the entire base and sub-grade from the weakening effect of water.
Constructed usually in two layers
- Binder Course
- Wearing Course (It is the layer which is in direct contact with the tyres of the vehicle)
Functions of Surfacing of Road:
- Prevent penetration of water in to the pavement
- Binder Course binds the Wearing Course with the Road Base
- Wearing Course provide a smooth riding
- Saves the lower layers from abrasion and weathering effects of the moving vehicles
- Made up of bituminous material
- For Flexible Pavement asphalt concrete is used
- For Rigid Pavements Reinforced Cement Concrete (RCC) is used
Others Components of Road Structure:
There are few component of road structure which are going to be discuss below which are as follows:
- FORMATION WIDTH
- ROAD MARGIN
- RIGHT OF WAY
Carriageway is the width of the road on which traffic moves without any restriction.it generally consist of traffic lines and the width of carriageway depend on the lines of traffic. Traffic lines are those lines on which traffic can move freely without any restriction. Each country has its own rules for the width of carriageway for insistence how long should it be in some country for single line road its 2.44m in some its more than that for two line its 3.75m in some more then that.
The formation width of road is the sum of carriageway, shoulders and separators (if there is any).
Kerb is the boundary line formed from stone or concrete block which separate the carriageway form footpath. There are different types of kerb with different types of height. There are four type of kerb which are low or mountable Krebs, semi-barrier kerb, barrier kerb, and submerged kerb. Iow kerbs are used for traffic to remain in line and also separate the shoulder from the road so the driver can enter the shoulder area with little difficulty its height is 10cm (4inch). A semi barrier kerb has height of 15cm (6inches). Barrier kerbs has a height of 20cm (8 inch). They are provided where pedestrian traffic is in considerable amount. Submerged kerb are used in rural roads the basically provide stability to the road pavement.
Medians are provided to isolate traffic. Their main area purpose is to restrict the collision of traffic that are moving in opposite direction of one another.
Camber or cross slope is provided in the middle of road or carriageway for the drainage of rain water form road surface. The main purpose of camber is to prevent water from entering to the subgrade of the road, the road quickly dries which prevent the traffic from slipping off the road which decrease the accident rate. The height of camber depends upon the material of road and the intensity of rain fall in the region. The value of the camber varies from 1 to 25 or 1 to 50.
Right of Way:
Right of way is the total land require for the construction of road. Which include carriages way, foot path, and future extension. The right of way depends upon the importance of the road for the future extension.
The part of road except carriageway are usually called road margin, it includes different parts or element of road which are given below
- Bus bays
- Parking lines
- Sidewalks or footpaths
- Service roads
- Cycle track
- Guard rails
- Drive way
- Frontage roads
Shoulders is a part of formation width except carriage way. Provided alongside the carriageway it’s basically a road for an emergency use for ambiance in rush hour or to stop a vehicle for repairing propose, and it can be used for the extension of road in future. The width of the shoulders is kept in between 2.5 m to 4.6 m.
Bus bays or bus stops are stationed on the side of road where the bus can stop safely to pick up passengers or drop off without disturbing the traffic flow they are provided at least 75m (250 feet) away from intersection of road.
In urban roads they usually provided parking on the road side and parallel parking is preferred because it does not disturb the traffic flow. Its width is 3m(10feet).
Sidewalks or Footpath:
Sidewalks and footpath is a same word When there is heavy amount of traffic and pedestrian flow a special paved area is provided for the pedestrian to walk safely on it without any accident.
Service roads are provided parallel to the main road and also connect to main highway, expressway. They are separated from the main road and are connected to highway at selected points. They are provided to not disturb the traffic flow.
Cycle track are provided in those areas where the cycle traffic volume is high than width of the cycle track is kept between 2 to 3 m or in other words (6 to10 feet).
Guard rails are usually provided on the shoulder of the road. If the fill is more than 3m (10 feet) they are provided. Their main is purpose to restrict them from falling of the road and to prevent them from serious accident. Guard rails are made of different types and in different shapes they are either made of steel, concrete or stone. They are painted white or yellow for better visibility.
Drive way join the highway with commercial organizations or buildings such as gas station, filling station, gasoline station, petrol station etc.
Frontage Roads is constructed to give acquire properties along an essential highway. It may be run parallel to the highway & segregated by separators.
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