Contents:

**Flexible Pavement Design by Semi Empirical Method**

Following are the semi empirical methods for flexible pavement design
- Triaxial test method
- Burmisterâ€™s method

### Triaxial Test Method of Flexible Pavement Design

In this method triaxial test is conducted on soil specimen under 160kN/m^{2}of lateral pressure. Hence modulus of elasticity is calculated from stress strain curve. Traffic coefficient X and saturation coefficient Y are introduced in this method. These are multiplied with the load system to get the total pavement thickness.

**Total pavement thickness by triaxial test method**

ADT (number) |
Traffic coefficient X |

40-400 | Â½ |

401-800 | 2/3 |

801-1200 | 5/6 |

1201-1800 | 1 |

1801-2700 | 7/6 |

2701-4000 | 8/6 |

4001-6000 | 9/6 |

6001-9000 | 10/6 |

9001-13500 | 11/6 |

13501-20000 | 12/6 |

Average annual rainfall (cm) |
Saturation coefficient (Y) |

38-50 | 0.5 |

51-64 | 0.6 |

65-76 | 0.7 |

77-90 | 0.8 |

91-100 | 0.9 |

101-127 | 1.0 |

### Burmisterâ€™s Method of Flexible Pavement Design

Burmister introduced a semi empirical method for the design of flexible pavements. In this method, he considered pavement as number of layers. And some assumptions are considered which are as follows:- The material in each layer is homogeneous
- The material is isotropic
- The material is elastic in nature
- Contact between the layers is continuous
- Unloaded top layer is free from normal and shearing stresses
- The surface layer is infinite in length (horizontal direction) and finite in depth (vertical direction).
- The underlying layers are infinite in both directions.

**For flexible pavements**

**For rigid pavements**

_{2}= deflection factor E

_{s}= modulus of the subgrade soil. Deflection factor is dependent of ratio of modulus of subgrade soil to the modulus of pavement material. So, from the below graph we can select the value of deflection factor corresponding to the ratio of base layer thickness to the radius of load that is h/a.

#### Procedure of Flexible Pavement Design by Burmisterâ€™s Method

In the Burmisterâ€™s design process, firstly conduct plate bearing test on the soil. The diameter of plate used is 30cm. now determine the modulus of subgrade soil. In the next step, determine the deflection factor from the below formula_{s}/E

_{p}) for the given value of (h/a ratio from the graph. Now for the design load (P) and tire pressure (p) determine the contact radius (a) from the below formula.

_{s}/E

_{p}ratio, select the appropriate h/a ratio from the above graph. And finally, by substituting contact radius (a) in h/a ratio we can get the value of base layer thickness (h).

**Read More:**

**Flexible Pavement Design by CBR Method**

**Flexible Pavement Design by Group Index Method**

**Flexible Pavement Composition and Structure**

**Types of Pavement - Flexible and Rigid Pavement**