24. The construction of a new collector highway is being planned. The following
ID: 1885290 • Letter: 2
Question
24. The construction of a new collector highway is being planned. The following information is available Highway length- 5000 ft L Highway width 60 ft W eW18 -(Acumulated ESAL)- 1,500,000 . Drainage takes about 1 hours and exposure levels approaching saturation occ of the time ralphalt concrete 400,000 lb/in.2 Mrbase -35,000 lb/in.2 l:Mrsubbase 10,000 lb/in.2 Sr3 Mrsubgrade9,000 lb/in.2 Monoavana D-10in R SN 2.8 Reliability: 90% .So-0.3 . 45APSI 4.5-2.52 Pt-2.5 .J-3.2 45 lb/in2 Elastic modulus of subgrade reaction, k Elastic modulus of concrete, Ec 3x106lb/in2 Mean concrete modulus of rupture, S700 lb/in2 . Unit price of PCC $150 per cubic yard Unit price of aggregate base course $35 per cubic yard . .Unit price of subbase material $30 per cubic yard Unit price of asphalt concrete $80 per cubic yard
Explanation / Answer
Given data:
L=5000 ft
W=60 ft
Assumptions:
(1) Collector street is made of either flexible pavement or rigid pavement
(2) All the values are obtained from AASHTO guide for design of pavements
Flexible pavement:
SN1=2.8
SN2=4.3
SN3=4.4
E.S.A.L=1.5x106
now determine the coefficients for a1, a2 and a3
SN1=a1d1
For a modulus resilience of 400,000 lb/in2 a1=0.4
d1=2.8/0.4
d1=7 in
For the base material, having Mr=35000 lb/in2 the value of a2=0.16
D2>(SN2-SN1)/a2m2
D2>(4.3-2.8)/(0.16x0.8)
D2>11.36 in
Use 12 in
Corrected SN*=0.16x12x0.8+2.8
SN2*=4.336
D3> (SN3-SN2)/(a3m3)
D3> (4.4-4.336)/(0.07x0.8)
D3> 1.14 in
This is very less, let us provide a GSB of 6 in thickness
D3=6 in
So the pavement will be having 7 in asphalt pavement, 12 in base and 6 in sub base
Cost of the flexible pavement=[7 inx5000ftx12x60 ftx12]x80/yard3+[12 inx5000 ftx12 inx60 ftx12]x35/yard3+[6 inx5000 ftx12 inx60 ftx12]x30/yard3
Cost=$518518+$38888+$166666
Cost=$1074072
Rigid pavement:
Ec=3x106
k=45 lb/in2
Sc=700 lb/in2
J=3.2
Cd=1.0
From the above given data and the charts
The minimum thickness required for the rigid pavement is 8.5 in, for the estimated load, standard deviation and reliability, d=10 in can be used
Cost for PCC layer=[5000x12x60x12x10 in]x150$/yard3
Cost=$1388888
The remaining components will remain the same except for asphalt
=$138,88,88+38,88,88+$166,666 (The base layer may be optional for rigid pavement)
Cost=$1944442
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