The type of low-cost road in which pavement structure is constructed with the soil available at the site is called earth road. It is also known as the earthen road. It is the cheapest type of road. It is best to construct when the budget or fund is limited. This type of road is generally found in rural and village areas.
Earth road can be improved further in the future according to the needs. For example: When traffic increases, the road has to be paved or gravelled to withstand more vehicular load. So, earth road can be easily improved further according to requirements.
Types of Earth Road
There are two types of earth road. They are:
1. Ordinary Earth Road
2. Stabilized Earth Road
1. Ordinary Earth Road
The earth road whose foundation and the wearing surface is made up of one or two compacted layers of natural soil along its alignment is ordinary earth road. It is the first stage in road construction.
a. It requires frequent maintenance. Mainly in the rainy season.
b. It is dusty and ruts are formed quickly.
c. It is not suitable for very heavy vehicles movement.
d. It is very economical to construct.
2. Stabilized Earth Road
The road whose foundation and the wearing surface is made up of one or two compacted layers of stabilized soil is called stabilized earth road.
Stabilized earth road is capable of withstanding high load and traffic. It is more durable than ordinary earth roads.
a. It doesn’t require frequent maintenance like ordinary earth roads.
b. Initial construction cost is more as compared to the ordinary road.
Selection of Material for Construction
The soil used in the construction should contain the following:
|S.N.||Base Course||Wearing Course|
|1||Clay Content||<5%||10 to 18%|
|2||Silt Content||9 to 32 %||5 to 15%|
|3||Sand Content||60 to 80 %||65 to 80 %|
|4||Liquid Limit||< 35 %||< 35 %|
|5||Plasticity Index||< 6 %||4 to 10 %|
1. Clay Content
a. Clay should not be more than 5 % in the soil if it has to be used in the base course. Excessive clay leads to deformation and settlement of road foundation.
b. Soil should contain 10 to 18 % clay if it has to be used in surface course.
2. Silt Content
a. Minimum of 9 % and a maximum of 32 % silt in the soil is best for base course.
b. The soil used in wearing course should contain a minimum of 5 % silt. More than 15% of silt is not suitable in any case.
3. Sand Content
a. About 60 to 80 % of sand in the soil is best for base course. Sand transfers the load by granular action. So, it is an essential component of soil used in the earth road.
b. 65 to 80% of sand in the soil is best to use in wearing course.
4. Liquid Limit
Liquid Limit of soil used in both base and wearing course should not be more than 35%.
5. Plasticity Index
a. The soil used in the base course should have plasticity less than 6 %.
b. Soil having the plasticity of 4 to 6% is suitable for the wearing course.
Earth Road Construction Procedure
Construction of earth road includes the following procedures:
a. Soil Survey
Soil survey is done to ensure the suitability of soil available at the site. It is done by visiting the site and determining the liquid limit and plasticity index.
Clay content, silt content and sand content are also analyzed.
Soil survey is done to locate the suitable borrow pits at the adjacent land that are easy to reach and at an economical haulage distance.
b. Fixing road alignment
The centre line and boundaries of the road are marked by driving the wooden pegs into the ground.
Pegs are also driven for the reference of the vertical profile of the road.
c. Material Preparation
Before excavation; organic materials like trees, shrubs and grasses are removed from the site.
d. Preparation of Subgrade
The steps in the preparation of subgrade are:
i. Clearing Site
The site can be cleared manually using tools like spade, pick, etc or by using machines like Bulldozer and scraper.
ii. Cutting and Filling of soil
Cutting and filling are done using excavators.
( Cutting: Removal of excessive soil
Filling; Addition of soil )
ii. Shaping of subgrade
The subgrade can be shaped by compacting with hand rollers, road rollers or dozers. Proper provision of slope gradient to the road should be ensured for drainage facility.
e. Spraying of Water
Water is spread above the subgrade so that it binds the soil added on it. If the moisture content in the soil and subgrade is sufficient then there is no need for the provision of water.
f. Addition of Layers
At first, one layer of soil is added on the subgrade. The thickness of the layer should not be more than 12 cm. After the addition of the layer, it is compacted using the roller.
If there is needed of another layer then the second layer is provided over first in the same way. Mostly, two layers are provided on earth roads.
g. Curing and Opening to Traffic
If sufficient moisture is absent then the road should be cured for 3 to 5 days according to the need of water to road.
The road should not be allowed for the public before 3 days after construction.
Precautions to be Taken During Construction
a. The camber should be very steep. This reduces the contact time of water with the road which increases durability. Generally, the slope between 1 in 20 to 1 in 33 is suitable.
b. The height of the embankment should be above 600 mm.
Advantages of Earth Road
Some of the advantages of earth road are given below.
a. It is economical to construct.
b. It can be constructed in very less time.
c. Local peoples and materials can be utilized in the construction of this road.
d. It can be easily improved further in future according to requirements.
Disadvantages of Earth Road
Some of the disadvantages of earth road are given below.
a. It is not suitable for heavy traffic and vehicles.
b. It is less durable and requires frequent maintenance.
c. Ruts and wears are quickly formed.
d. Not workable during monsoon season.
e. It is dusty. ( Mixing of soil particles in surrounding air and making smoke like the environment of dust.)