Civil Engineering ETDs


Nayan Saha

Publication Date



Reliability is an important factor in flexible pavement design to consider the variability associated with the design inputs. In this study, subgrade strength variability and flexible pavement designs are evaluated for reliability. The effects of weak subgrade on pavement design and performance prediction are evaluated through a case study using Mechanistic-Empirical Pavement Design Guide (MEPDG). Permanent deformation or rutting is very sensitive to subgrade strength. International roughness index (IRI) is sensitive to the subgrade strength. Six existing pavement sections' design data are studied to examine the effect of variability associated with subgrade strength and selection criteria of subgrade strength for design. Parameters such as: mean, maximum likelihood, median, coefficient of variation and density distribution function of R-value are determined. A sub-section procedure is employed to deal with variability associated with subgrade strength in flexible pavement design. A single design for roadway sections does not yield an effective design regarding target reliability, while the sub-sectioning procedure is presented as a better way to deal with the subgrade variability. Minimum R-value assessment for making the decision of sub-excavation is also performed. Design outputs are compared for mean, maximum likelihood and median R-value inputs in terms of reliability and thickness using different design procedures. The reliability of the flexible pavement design is also evaluated for hot mix asphalt (HMA) properties in this study. Alternative designs are recommended for the existing pavements by modifying material inputs to mitigate different distresses with target reliability.


Pavements--Subgrades--Evaluation, Pavements, Flexible--Evaluation.


New Mexico Department of Transportation

Document Type




Degree Name

Civil Engineering

Level of Degree


Department Name

Civil Engineering

First Advisor

Tarefder, Rafiqul A.

First Committee Member (Chair)

Stormont, John C.

Second Committee Member

Ng, Percy