Flexible Pavement | Rigid Pavement | Semi Rigid Pavement | ESWL | Contact Pressure

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Pavements are generally classified into two categories on he basis of structural behavior-
(i) Flexible Pavement (ii) Rigid Pavement

Flexible Pavement-

The pavement which have very less flexural strength is called Flexible Pavement. This type of pavement transmit the load to the lower layer by grain to grain transfer. A typical flexible consist of four components. These are-

(a) Soil Sub-grade (b) Sub base Course (c) Base Course (d) Surface Course
The examples of flexible pavements are Bituminous concrete, granular materials with or without bituminous binders, water bound macadam etc. There will neither expansion nor contraction joints are provided in the flexible pavement. Cost of Completion of flexible pavement are less but have high maintenace cost.

Pavement

Rigid Pavement-

This pavements are those which possess worthy flexural strength. The rigid pavement transmit the wheel load stress through a wider area below by slab action. The rigid pavements are made of portland cement concrete.The plain cement concrete slabs are expected to take up about 40 kg/cm2 flextural stress.Joints are used in the construction of rigid pavement and has high completion cost but low maintance cost. Rigid pavement has mainly three components-
(a) Soil Subgrade (b) Base Course (c) Cement Concrete Slab

Semi Rigid Pavement- A semi rigid pavement is the intermediate stage between the flexible and the rigid types and It devices strength by both load-spreading and flexural action.

Design Wheel load-

(a) Maximum Wheel load- Total load influence the thickness requirements of pavements and the tyre pressure influence the quality of surface course. The maximum legal axle load as specified by IRC is 8170 Kg with a maximum equivalent single wheel load of 4085 kg.

(b) Contact Pressure and Tyre Pressure or Inflation Pressure-

At low type of pressure the tyre comes under compression. So, Contact pressure is greater than tyre pressure.

Contact pressure = Load on wheel / Contact area.

At high tyre pressure, tyre come under tension. So, contact pressure is less than tyre pressure.

This is defined as load on single tyre which will cause an equivalent magnitude of stress, strain , deflection etc. at a given location to that of a multiple wheel load at the same location.

Equivalent Single Wheel Load ( ESWL ) is calculated by using equal stress criteria.It is a semi-rotation method, known as Boyd and Foster method, Based on Following assumption-

1. Equalancy concept is based on equal stress.

2. Contact area is circular.

3. Influence angle is 45 Degree.

4. Soil medium is elastic, homogenous and isotropic.

Group Index Method-

This method is a empirical method based on physical properties of sub grade soil. The higher value of group index represents the weaker soil sub grade, the greater will be the thickness of pavement. The group index values of soils vary from 0 to 20.

To know more about Geometric Design of Highway- https://www.civilengineerknowledge.com/2018/11/geometric-design-of-highway.html

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