Tuesday, January 21, 2014

Factors affecting design of pavements

Design of pavement consist of two parts:

  1. Design of the mix to be used as the material for different layers.
  2. Design of the thickness of the different pavement layers.
In this post I will discuss here the various factors which are considered while designing the pavement thickness.

  1. Design Wheel Load
  2. Type of sub-grade
  3. Climatic conditions
  4. Properties of the pavement layers
  5. Environmental conditions
  6. Other special conditions.
  • Design Wheel Load: Design wheel load is the main factor which decides the thickness of the pavement. Of course higher the design wheel load larger will be the pavement thickness. There are other factors related with the design wheel load. 
         Total Design wheel load, Magnitude of contact pressure, repetition of load and dynamics of load is analyzed. Total thickness is governed by the total design wheel load and the quality of         the surface material is governed by the magnitude of the contact pressure. 

Higher speed of the load will result in lesser contact time and thus the deflection of the pavement will be less but if the pavement is undulated then the impact will be higher when speed is higher so, dynamics plays an important role.
  • Type of Subgrade : Subgrade quality is determined by various tests such as CBR test, Tri-axial test, plate load test etc. When this possess high strength the thickness required will be less and vice verse.

  • Climatic conditions: Amount of rainfall and subsequently the moisture affects the moisture in the sub-grade. The daily and seasonal variation of the temperature also affect the design of flexible and rigid pavements. 
If freezing occurs in the winter then there are chances of frost action on the subgrade soil and so this should be considered while the design of the pavement.
  • Properties of the pavement layers: Performance of the pavement layers depends on the properties of the materials used in the layers. The fatigue and their performance under the adverse environmental conditions should be tested beforehand and should be given due considerations.

  • Environmental Conditions: Environmental factors such as, height of the embankment,  foundation details, depth of cutting and the level of the water table affects the design of pavements. Variation in temperature daily or seasonal induces the warping stresses in case of rigid pavements.

  • In case of semi-rigid pavement materials, the formation of the hair cracks, their propagation has to studied before arriving at a specific method of design of the semi-rigid pavement.

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