Pavement Structural Analysis of the Design Recommendations for ...

Pavement Structural Analysis August 2004
Report No. 15953-2/1 ARA-ERES Consultants
Number of Monthly Tridem Axle Loads
3500
3000
2500
2000
1500
1000
500
0
0 20 40 60 80 100 120
Tridem Axle Load, kips
Figure 4 Monthly tridem axle load distribution or spectra for the base year for
the segment of I-96 from M-39 to Schaeffer Road.
For the simplistic M-E analysis procedure, the design values recommended for use by the
Michigan DOT were used in the design computations and checks because of the different
types of trucks typically used in Michigan, as compared to other agencies from traffic
data included in the LTPP database. Re-analyzing the Weighing-In-Motion (WIM) data
for selected Michigan sites was beyond the scope of work for this thickness design study.
3.2 Subsurface Investigations – Soil Support Design Value
The logs of sixty-nine 5-fott (1.5-meter) borings were provided to determine the types of
soils along this project. The soils along this portion of I-96 consist of varying thickness of
fill or topsoil over a low plasticity, firm silty clay.
The effective resilient modulus of the foundation soil is a design parameter required by
the 1993 AASHTO Design Guide and M-E design procedures. The resilient modulus is
determined from repeated load triaxial tests, and can have a significant impact on the
flexible pavement layer thickness. Resilient modulus tests were unavailable for the soils
along this roadway. The Michigan DOT used a design resilient modulus of 3,000 psi
(20,684 kPa) in the AASHTO design. This design resilient modulus is based on
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