Flexible Pavement | Transportation Engineering - Civil Engineering (CE) PDF Download

Introduction

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.
    Flexible Pavement | Transportation Engineering - Civil Engineering (CE)

(i) Stress Under Road Surface as per Boussineq’s Equation,
Flexible Pavement | Transportation Engineering - Civil Engineering (CE)
where,
σz = vertical stress at depth z.
q = surface pressure.
z = depth at which σz is computed.
a = radius loaded area.
Flexible Pavement | Transportation Engineering - Civil Engineering (CE)

(ii) As per IRC
Maximum legal axle load = 8170 kg
Equivalent single wheel load = 4085 kg.
(iii) Contact pressure
Flexible Pavement | Transportation Engineering - Civil Engineering (CE)
(iv) Rigidity factor (R.F)
Flexible Pavement | Transportation Engineering - Civil Engineering (CE)
Flexible Pavement | Transportation Engineering - Civil Engineering (CE)

(v) Equivalent Single Wheel Load (ESWL) 
Flexible Pavement | Transportation Engineering - Civil Engineering (CE)
Flexible Pavement | Transportation Engineering - Civil Engineering (CE)

Methods of Flexible Pavement Design

(i) Group Index Method
G.I = 0.2a + 0.005ac + 0.01bd

(ii) C.B.R Method
(a) 
Flexible Pavement | Transportation Engineering - Civil Engineering (CE)
Flexible Pavement | Transportation Engineering - Civil Engineering (CE)

(b) The thickness of Pavement, (T)
Flexible Pavement | Transportation Engineering - Civil Engineering (CE)
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,
Flexible Pavement | Transportation Engineering - Civil Engineering (CE)
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
Flexible Pavement | Transportation Engineering - Civil Engineering (CE)
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.
Flexible Pavement | Transportation Engineering - Civil Engineering (CE)
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)
Flexible Pavement | Transportation Engineering - Civil Engineering (CE)
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,
Flexible Pavement | Transportation Engineering - Civil Engineering (CE)
where, EP = Modulus of elasticity of pavement material
T1/T2 = (ES)/(EP)1/3

(v) MC Load Method
T = k.log10(P/S)
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,
Flexible Pavement | Transportation Engineering - Civil Engineering (CE)
where, μs and μp are Poisons ratio for soil subgrade & pavement.
For single layer, F2 = 1
P = Yielded pressure
ES = Subgrade modulus
a = Radius of loaded area

The document Flexible Pavement | Transportation Engineering - Civil Engineering (CE) is a part of the Civil Engineering (CE) Course Transportation Engineering.
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