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3 years ago

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Using the AASHTO procedure, determine the thickness required for a base and a surface layer over existing subgrade. The structur

al number required for this pavement is 4.5. The available materials are a crushed stone base course with a material layer coefficient of 0.13 and an HMA surface with a material layer coefficient of 0.40. The drainage coefficient of the based course can be considered as 0.90.

1 answer:

garri49 [273]3 years ago

7 0

Answer:

<u>the thickness required would be 12 inch HMA and granular base layer of 6 inches</u>

Explanation:

structural number = 4.5

stone base course material coefficient = 0.13

hma material layer coefficient = 0.40

drainage coefficient = 0.90

we will use layered analysis procedure to get thickness

D1 >= sN1/a1

when we cross multiply,

sN1 = a1D1 >=sN1

D2 >= -sN2-sN1/a2m2

sN2* + sN1* >= sN2

D3 >= sN3-(sN1*+sN2*)/a2m2

where a1,a2,a3 = layer coefficient

d1 d2 d3 = actual thickness

m2,m3 = coefficient of base

a1 = 0.4

a1 = 0.13

sN = 4.5

m2 = 0.9

D1 >= sN1/a1 = 4.5/0.4

= 11.25

thickness of surface = 12 inches

a1D1 = 0.4x12 = 4.8

we have value of sN2 = 5.5

(5.5 -4.8)/(0.13*0.9)

= 0.7/0.117

= 5.9829 inches

approximately 6 inches

so the pavement will have 12inch HMA surface and 6 inches granular base layer.

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$\Delta P = \frac{S\cdot \rho_{w}\cdot g \cdot \Delta h}{1000}$ (Eq. 1)

Where:

$S$ - Relative density, dimensionless.

$\rho_{w}$ - Density of water, measured in kilograms per cubic meter.

$g$ - Gravitational acceleration, measured in meters per square second.

$\Delta h$ - Height difference in the U-tube manometer, measured in meters.

$\Delta P$ - Gas pressure difference, measured in kilopascals.

If we know that $S = 1.5$ , $\rho_{w} = 1000\,\frac{kg}{m^{3}}$ , $g = 9.807\,\frac{m}{s^{2}}$ and $\Delta h = 0.286\,m$ , then the pressure difference is:

$\Delta P = \frac{1.5\cdot \left(1000\,\frac{kg}{m^{3}} \right)\cdot \left(9.807\,\frac{m}{s^{2}} \right)\cdot (0.286\,m)}{1000}$

$\Delta P = 4.207\,kPa$

The pressure difference is 4.207 kilopascals.

2) From Physics we remember that a pound per square unit equals 2.036 inches of mercury and 2.307 feet of water and we must multiply the given pressure by corresponding conversion unit: ( $p = 2.5\,psi$ )

$p = 2.5\,psi\times 2.037\,\frac{in\,Hg}{psi}$

$p = 5.093\,in\,Hg$

$p = 2.5\,psi\times 2.307\,\frac{ft\,H_{2}O}{psi}$

$p = 5.768\,ft\,H_{2}O$

2.5 pounds per square inch equals 5.093 inches of mercury and 5.768 feet of water.

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4 years ago