Flexible Pavement

By Shreya Laddha|Updated : December 2nd, 2021

Through Champion Study Plan for GATE Civil Engineering (CE) 2022, we are providing Flexible Pavement study notes and other important materials on every topic of each subject.

These topic-wise study notes are useful for the preparation of various upcoming exams like GATE CivilIESBARCISROSSC-JEState Engineering Services examinations and other important upcoming competitive exams.

The article contains fundamental notes on the "Flexible Pavement"  topic of the "Highway Engineering" subject. 

Flexible Pavement 

Flexible Pavements

Flexible pavements are those, which on the whole have low or negligible flexural strength and are rather flexible in their structural action under the loads.

A typical flexible pavement consists of four components: 1. soil subgrade 2. sub-base course 3. base course 4. surface course.

image001

(i) Stress Under Road Surface as per Boussineq’s Equation,

image002

where,

σz = vertical stress at depth z.

q = surface pressure.

z = depth at which σz is computed.

a = radius loaded area.

image003

(ii) As per IRC

Maximum legal axle load = 8170 kg

Equivalent single wheel load = 4085 kg.

image004

image005

(v) Equivalent Single Wheel Load (ESWL

image006

image007

Methods of Flexible Pavement Design

(i) Group Index Method

G.I = 0.2a + 0.005ac + 0.01bd

(ii) C.B.R Method

(a) 

image008

image009

(b) The thickness of Pavement, (T)

image010

where, P = Wheel load in kg.

CBR = California bearing ratio in percent

p = Tyre pressure in kg/cm2

A = Area of contact in cm2.

A=πa2

a = Radius of contact area.

(c) Number of a heavy vehicle per day for design (A),

A=P[1+r](n+10)

where, A = No. of vehicles at the end of design period.

P = Number of heavy vehicles per day at least count.

r = Annual rate of increase of heavy vehicles

n = Number of years between the last count & the year of completion of construction.

(d) CBR Method of pavement design by cumulative standard axle load,

image011

where,

Ns = Cumulative number of standard axle load

A’ = Number of the commercial vehicle per day when construction is completed considering the number of lanes.

n = Design life of the pavement, taken as 10 to 15 years.

F = Vehicle damage factor.

D = Lane distribution factor

(iii) California Resistance Value Method

image012

where, T = Total thickness of pavement, (cm)

k = Numerical constant = 0.166

T.I = Traffic Index

T.I = 1.35(EWL)0.11

R = Stabilometer resistance value

C = Choesiometer value.

image013

where, T1 & T2 are the thickness values of any two pavement layers & C1 & C2 are their corresponding Cohesiometer values.

(iv) Triaxial Method

(a) Thickness of pavement required for single layer, (TS)

image014

where, TS = Thickness in cm

P = Wind load in kg

X = Traffic coefficient

Y = Rainfall coefficient

ES = Modulus of elasticity of subgrade soil (kg/cm2)

a = Radius of contact area (cm)

Δ = Design deflection (0.25 cm)

(b) Thickness of Pavement Consist of Two layer system,

image015

where, EP = Modulus of elasticity of pavement material

image016

(v) MC Load Method


image017

where, T = Required thickness of gravel base (cm)

P = Gross wheel load, (kg)

k = Base course constant.

(vi) Burmister Method (Layered System)

Displacement equations given by Burmister are,

image018

where, image019 are Poisons ratio for soil subgrade & pavement.

For single layer, F2 = 1

P = Yielded pressure

ES = Subgrade modulus

a = Radius of loaded area

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