QUANTIFICATION OF THE IMPACT OF SUBGRADE SWELLING IN PAVEMENT DESIGN

Abstract

Accurate prediction of the impact of environmental factors on pavement serviceability is important for a pavement design. In this regard, AASHTO Pavement Design Guidelines (1986) provide a rational method of incorporating the effects of roadbed swelling and frost action. According to the AASHTO (1986) procedure, the present serviceability index (PSI) loss of a pavement segment due to environmental factors is estimated by considering factors such as the moisture supply as well as the fabric, swelling potential and frost susceptibility of the roadbed soil. The swelling potential in turn is governed by the plasticity index of the soil and compaction conditions. The current AASHTO procedure requires most of the above attributes to be qualitatively adjudged. Hence, the designer is called upon to use linguistic assessments as “low rainfall”, “poor drainage”, “tight soil fabric”, “normal field moisture and density conditions” and etc. to evaluate them. Consequent to the use of such vague descriptions, the repeatability of the PSI loss estimation procedure is affected.

In this paper, the author advances a fuzzy set theoretic approach that enables the evaluation of PSI loss to be accomplished in a better defined and repeatable manner using the same AASHTO procedures. In this approach, the designer's linguistic assessments of the relevant attributes are transformed to well defined fuzzy sets stored in the computer. At this stage of the development, dictated by the AASHTO guidelines, fuzzy sets mathematics principles take over the manipulation process to predict the PSI loss ensuring repeatability and consistency. While the new technique is illustrated by a sample design problem, the impact of the chosen membership function is also scrutinized.

KEY WORDS:

• Pavement
• swelling
• fuzzy sets