2.for Rural LOw Volume Traffic Rigid Pavement Design

8/11/2019 2.for Rural LOw Volume Traffic Rigid Pavement Design

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CONCRETE PAVEMENT DESIGN FOR RURAL

ROADS

Background:

Concrete pavements or rigid pavements offer an alternative to

flexible pavements especially where

the soil strength is poor,

the aggregates are costly and

drainage conditions are bad

road is passing though villages & water-logged areas


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CHOICE OF PAVEMENTS:

The choice of pavement depends on:

1. Local soil strength

2. Availability of construction materials

3. Seriousness of drainage aspects

4. Alignment of roads (if passing village & if it iswater logging area)

5. Life-cycle cost


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OPTIONS OF CONCRETE PAVEMENTS (for rural

roads):

1. Conventional screed-compacted pavements

2. Roller Compacted Concrete Pavements (RCCP)

3. Interlocking Concrete Pavements (ICBP)


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1. Wheel load

2. Tyre Pressure

3. Design period4. Characteristics of the Subgrade

5. Sub-base

6. Concrete Strength

7. Modulus of elasticity and Poissons Ratio

8. Coefficient of Thermal Expansion

FACTORS GOVERNING DESIGN for

Rural Roads


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1. Wheel load

The legal axle load is 102 kN

Therefore , the pavement may be designed for

51 kN

For link roads serving villages where traffic consists of agricultural

tractors and trailers and light commercial vehicles only, a design

wheel load of30 kN may be considered


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2. Tyre Pressure

For a wheel load of 51 kN, 0.7 MPa may be considered

For 30 kN wheel load, 0.5 MPa may be

considered


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3. Design Period

Minimum 20 years is considered

Wheel load repetitions and fatigue life

consumption concept is not recommended in

IRC:SP:62-2002


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4. Characteristics of the Subgrade

In case of rigid pavement design, modulus of subgrade

reaction, k-value is important & is determined in

accordance with IS:9214-1974 (750 mm dia plate is

recommended)

k750 = 0.5 k 300If plate other than 750 mm dia isused

k-value is desirable to determine during or soon after the rainy

season, since subgrade strength is affected by the moisture

content.


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Approximate k-value corresponding to

soaked CBR values


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5. Sub-base

Sub-base layer is provided for the following reasons:

1. This layer provides a uniform and reasonably firm support

2. This layer prevents mud-pumping on sungrade of clays &

silts

3. This layer acts as leveling course on distorted, non-uniform

and undulating subgrade

4. This layer acts as a capillary cut-off


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For wheel load design of 51 kN

-150 mm thick WBM using 53-22.4 mm aggregate

-GSB

-Soil-cement or Soil-Lime

Choice of sub-base:

For wheel load design of 30 kN

-75 mm thick WBM


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The effective k-value may be taken as 20% more than

the k-value of the subgrade

If WBM/ GSB/Soil-cement/Soil-lime bases are used as

sub-base

Separation Membrane

A plastic sheet of 125 microns thickness is normallyprovided over the sub-base to act as a separation layer

b/w sub-base and concrete slab


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In case of rigid pavement, slab is failed due to bending

stresses, it is necessary that slab design is based on

the flexural strength of concrete

6. Concrete Strength

If no facilities for flexural strength determination

Concrete mix design may be carried out based on

compressive strength values

Fcr = 0.7 fck

Fck = characteristic compressive strength (MPa)

(1)


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7. Modulus of Elasticity and Poissons Ratio

E-value may be taken as 3.0 x 104 MPa

Poissons ratio may be 0.15

8. Coefficient of Thermal Expansion

= 10 x 10-6 per 0C


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DESIGN OF SLAB

THICKNESS


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Factors affecting design of pavement thickness

are:

1. Traffic loads

2. Temperature variations

3. Effect of moisture changes

4. Shrinkage effects

Considered not critical

to thickness design due

smaller magnitude


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CRITICAL LOAD POSITIONS

Critical load positions take placed in three

locations:

1. Interior loading

2. Edge loading

3. Corner loading


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Interior loading

Westergaardconsidered interior

loading as a case

when the load is

applied at a

considerable distance

from the pavement

edge

i = max stress at interior loading kg/cm2

h = slab thickness, cm

W = wheel load, kg

= radius of relative stiffness, cm

b = radius of resisting section, cm

(2)


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Corner loading

Corner loading (tensile

stress at slab top)

a = radius of wheel contact area, cm

Where b=a when a 1.724h;

When a < 1.724hb =

(4)

(5)
http://classes.engr.oregonstate.edu/cce/winter2012/ce492/Modules/06_structural_design/curling_example.htm#radius_of_relative_stiffnesshttp://classes.engr.oregonstate.edu/cce/winter2012/ce492/Modules/06_structural_design/curling_example.htm#radius_of_relative_stiffnesshttp://classes.engr.oregonstate.edu/cce/winter2012/ce492/Modules/06_structural_design/curling_example.htm#radius_of_relative_stiffness


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Different axle load positions causing tensile

stress at the top of the slab with tied shoulder


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The least stress is induced in the

interior where the slab is

continuous in all directions

Interior slab

Magnitude of

stress under the

action of load

Edge stress

Corner stress

Under the action of load

Maximum stress is induced in the

corner region as the corner isdiscontinuous in TWO directions

especially when dowel bars are not

provided in rural roads

The edge being discontinuous in

one direction only has lower stress

in comparison to corner region


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Therefore, design of slab thickness is based on the more

critical condition of the two

(i) Edge stresses

(ii) Temperature differential

(iii) Corner stresses

CALCULATION OF STRESSES

1. Edge stresses

(i) Due to load

(ii) Due to temperature


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(7)


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Recommended

temperaturedifferentials for

concrete slab


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Corner Stress

It can be found by using Westergaards analysis modified by

Kelley

(9)


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DESIGN CHART

Fig. 1


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DESIGN CHART

Fig. 2


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DESIGN CHARTFig. 3


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DESIGN CHART

Fig. 4


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DESIGN PROCEDURE

Decide joint spacing and lane width

Select tentative design thickness of slab, based on defined

design load, k-value/CBR & flexural strength of concrete

Ascertain maximum temperature stress for the criticaledge region (Eqn 8) or Fig. 5

Calculate the residual available strength of

concrete for supporting traffic loads region

Ascertain edge load stress from (Eqn 6) or Fig

1 &3 and calculate the factor of safety


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In case the availability factor of safety is less than or far

in excess of 1, adjust the tentative slab thickness andrepeat above steps till factor of safety is 1 or slightly more

Check the adequacy of thickness in the corner region byascertaining corner load stress from eqn (9) or Figs 2 or

4


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CONCRETE PAVEMENT THICKNESS FOR RURAL ROADS

Maximumtemperature is

considered in the

computation

Design thickness

values are based onthe 90-day strength

Following design

parameters have

been considered inpreparing this table


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THANK YOU

Documents

2.for Rural LOw Volume Traffic Rigid Pavement Design