A flexible pavement section is designed using a CBR of 20 for the subgrade. During construction it is found that the subgrade is softer with a CBR of 7. The contractor proposes to place a layer of select fill on top of the subgrade to compensate for this condition. How thick should the select fill layer be if the original pavement section is 8 inches HMA over 12 inches crushed aggregate base over subgrade. Assume a resilient modulus of 15,000 psi for the select fill and clearly describe the design method used to solve this problem as well as any assumptions and results

A flexible pavement section is designed using a CBR of 20 for the subgrade. During construction it is found that the subgrade is softer with a CBR of 7. The contractor proposes to place a layer of select fill on top of the subgrade to compensate for this condition. How thick should the select fill layer be if the original pavement section is 8 inches HMA over 12 inches crushed aggregate base over subgrade. Assume a resilient modulus of 15,000 psi for the select fill and clearly describe the design method used to solve this problem as well as any assumptions and results

Traffic and Highway Engineering

5th Edition

ISBN:9781305156241

Author:Garber, Nicholas J.

Publisher:Garber, Nicholas J.

Chapter20: Design Of Rigid Pavements

Section: Chapter Questions

Problem 17P

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The following figure shows concrete pavement with the layer thickness and elastic modulus as indicated. Assume modulus of rupture of 650 psi, load transfer coefficient of 3.2, serviceability loss from 4.5 to 2.5, and drainage coefficient of 0.9. The bedrock depth and loss of support is not considered for the subgrade. Use the design equation or monograph with 50% reliability to solve the following: 1) Determine the number of ESAL that the pavement can carry before failure. 2) If the daily traffic has 1080 single axles (20-kip), 400 single axles (24-kip), and 680 tandem axles (40-kip), and the annul traffic is the same over the design period, how many years would the concrete pavement last before failure? 8-inch Portland Cement Concrete Ec=4×106 psi 8-inch Granular Subbase Ec=30,000 psi Subgrade Mr = 5000 psi
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