You need to determine a pavement system for the new County Road D. You look at b
ID: 1711004 • Letter: Y
Question
You need to determine a pavement system for the new County Road D. You look at both rigid and flexible pavement designs. You perform a geotechnical investigation and find the following:
% Passing #10 Sieve – 95%
% Passing #40 Sieve – 65%
% Passing #200 Sieve – 40%
Liquid Limit = 55%
Plastic Limit = 35%
What is the AASHTO Soil Classification and the Group Index. What is the estimated CBR based on the Geotechnical Investigation?
Due to the new steel plant, your traffic surveys determine that the percent of trucks using the roadway is 30%. Talking with the plant and local planning authorities, you estimate the ADT will increase at a rate of 1% per year for the 20-year design life of the new road. Determine the ESALs to design the road using ODOT standards. (One year past midpoint method).
Find the Minimum SN for a flexible pavement system. Design a flexible pavement section assuming that you will use 8” of Item 304 Aggregate Base (The local quarry will appreciate your business). You will use 1.5” of surface course, 2” of intermediate course, with the remainder using an asphalt concrete base course.
Design a rigid pavement system assuming you will use 8” of Item 304 Aggregate Base for the subbase. Assume that you would use asphalt shoulders.
Explanation / Answer
Group Index = 0.2a + 0.005ac + 0.01bd
a= percentage of soil passing 0.074 mm sieve in excess of 35 per cent, not exceeding 75.
b= percentage of soil passing 0.074 mm sieve in excess of 15 per cent, not exceeding 55.
c= Liquid limit in per cent in excess of 40.
d= Plasticity index in excess of 10
GI = 0.2(50) + 0.005(50)(15) + 0.01(25)(0)
= 13.75
AASTHO Classification:
According to AASTHO soil classification chart the soil with given percentage fines and Atterberg's Limits fall under group A-6.
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