Flexible Pavement Distresses Notes

7/25/2019 Flexible Pavement Distresses Notes

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Pavement distresses and serviceability

Atul Narayan, S. P.

IIT Madras

September 6, 2015


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Outline

Introduction

Pavement distress models

Incremental damage


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Outline

Introduction


Incremental damage


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Subordinate learning objectives

To analyze the stress-strain distribution in pavements for given

loading conditions.

To estimate pavement distresses based on stresses and

strains in pavement structure.

To explain the effect of mechanical properties on pavement

behavior and performance.

To analyze the stresses and distresses caused by vehicle

loading.

To estimate the expected volume of traffic in design life


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Outline

Introduction


Incremental damage


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Fatigue model for pavements

Nf =k1 1t

k2 1

Ek3

(1)

where

Nfis the number of repetitions to failure by fatigue

tis the horizontal tensile strain at the bottom of the

HMA layer

Eis the elastic modulus of HMA layer

ki, i =1, 2, 3 are constants found from laboratory

testing

Failure corresponds to 50% of the pavement surface area

covered with alligator cracking.

IRC, Asphalt Institute, Shell Bitumen and MEPDG uses it.

The model essentially implies that fatigue life decreases with

increase in the horizontal tensile strain or elastic modulus of

HMA layer.


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Rutting model for pavements

Nr =k4k5v (2)

where

Nris the number of repetitions to failure by rutting

vis the vertical compressive strain at the top of the

subgrade

ki, i =4, 5 are constants

Failure corresponds to rut depth being more than 25 mm.

This model assumes there is permanent deformation only in

the subgrade

In reality, most permanent deformation occurs in the HMA

layer, especially when it is thick.


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Outline

Introduction


Incremental damage


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Introduction

Traffic is not homogeneous.

Material properties change with daily, monthy and seasonalvariations.


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Miners rule or Linear damage hypothesis

Damage is a parameter characterizing the state of a materialsuch that:

It is 0 for an undamaged material It is 1 for a material that has experienced complete failure.

IfNrepetitions of a loadL causes complete failure (i.e. damage

equal to 1), then the damage caused by any single repetition of the

loadL is

1

N


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Miners rule or Linear damage hypothesis (cont.)

Linear damage hypothesisIfN1 repetitions of some cyclic loading L1 causes complete failure

andN2repetitions of another cyclic loadingL2 also causes

complete failure, the damage due ton1 repetitions ofL1 andn2

repetitions ofL2 isn1D1 + n2D2 =n1

N1+

n2

N2

It was first proposed by A. Palmgren and popularized by M.

Miner.

Miner (1945) proved that the total work that can be absorbed

until failure has a constant value.


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Miners rule applied to pavement failure

Nijis the number of repetitions of ith vehicle group to failure inthejth time period.

The damage per passing of a particular vehicle at a particular

time period is

Dij =1

Nij (3)

It is assumed that the total damage to the pavement structure

is the sum of the damage due to individual load repetitions.

DTotal =ji

niNij

(4)


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Activity 1

There are two types of trucks that use a particular highway section,

Truck A and Truck B. Every year, 1 million trucks pass through the

highway section of which 40% are truck type A and the remaining

60% are of truck type B. If 10 million repetitions of Truck A causes

complete failure and 8 million repetitions of Truck B also cause

complete failue, how long would the pavement last?

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Flexible Pavement Distresses Notes