INCORPORATION OF RELIABILITY INTO NIGERIAN EMPIRICAL MECHANISTIC PAVEMENT ANALYSIS AND DESIGN SYSTEM (NEMPADS)

INCORPORATION OF RELIABILITY INTO NIGERIAN EMPIRICAL MECHANISTIC PAVEMENT ANALYSIS AND DESIGN SYSTEM (NEMPADS)

Abstract:

This work was aimed at providing the most appropriate Nigerian Empirical-Mechanistic Flexible Pavement Analysis and Design method (NEMPAD) by incorporating Reliability, using First order reliability method (FORM), considering all the input variabilities, uncertainties, and seasonal variations, with the aid of Matlab to express the algorithms. A frame work was developed for computation of component reliability index (R.I), system reliability index (R.I), and probability of failure. Inputs parameters considered includes: traffic load, material properties, and environmental conditions. Four seasons were considered in the design namely: Hunturu(1 week Dec-2 week Feb), Bazara(2 week Feb-2 week May), Damina(2 week may-1 week Oct), and Kaka(1 week Oct-1 week Dec) seasons, for the North West geographical zone, and the cumulated damage was computed for each season. Comparism was made between deterministic and reliability methods. The results indicates that at coefficient of variation (COV) of 25% , a surfacing thickness of 100mm (representing wearing and binder course), 165mm thickness of Base course material, and 180mm thickness of sub base course material, are adequate, while at coefficient of variation (COV) of 42% a surfacing thickness of 100mm (representing wearing and binder course), 200mm thickness of Base course material, and 250mm thickness of sub base course material, are adequate, as against the deterministic method cited in Olowosulu (2005),where higher thicknesses were used, under the same traffic load and conditions. The results also indicated that highest level of damage with respect to fatigue was recorded during Bazara season due to the effects of Temperature, while highest level of damage with respect to Rutting was recorded during Damina season due to the effects of water in the subgrade.

INCORPORATION OF RELIABILITY INTO NIGERIAN EMPIRICAL MECHANISTIC PAVEMENT ANALYSIS AND DESIGN SYSTEM (NEMPADS)