MECHANISTIC-EMPIRICAL APPROACH FOR THE ANALYSIS OF SUBGRADE AND GRANULAR LAYERS OF FLEXIBLE PAVEMENT USING IITPAVE AND KENPAVE

Abstract

Premature failure of pavements is a severe issue that affects many regions, though the causes can vary. The majority of design procedures assume that the subgrade is lying approximately 500 mm above the high flood level. But heavy rainfall causes a segment of the pavement, or even the entire structure to be submerged in several areas of the country. For rural roads, where pavements are built on the available land without even providing embankment, the issue is more serious. According to the results of numerous research, subgrade soil loses strength over time when it is submerged. Additionally, a drop in the subgrade's rutting life and fatigue value is seen. Also, a submerged subgrade exhibits higher damage and decreased structural strength due to a drop in the elastic moduli of the granular and subgrade layers, as well as an abrupt jump in roughness index (as determined by the International Roughness Index). In order to maintain adequate strength and resilience to support the imposed traffic load regardless of unfavourable conditions like severe rainfall and flooding, subgrade soil must have an appropriate value of CBR. The elastic moduli of the subgrade and granular layers can be enhanced by a properly stabilized subgrade, which can also provide long-term performance and improve the CBR. The use of geosynthetics and geogrids as reinforcement is one of the strategies used today to strengthen subgrade and granular layers. Using pavement design software’s such as IITPAVE and KENPAVE, this study examined the effects of improving the elastic moduli of the subgrade and granular layers associated with an increase in CBR as well as the effect of varying the thickness of the pavement layers over various mechanistic empirical parameters. Through damage analysis in KENPAVE, the study also evaluates the extent of pavement damage. The analysis shows that, the damage associated with the pavement structures for modified cases are reduced by about 45%, from the conventional cases, and hence design was modified. The effect of variation on the pavement performance parameters due to the change in bituminous course and Granular base and subbase course thicknesses by ±25%, designed for improved material properties and effective CBR, was also examined and from the results, an increase in fatigue and rutting lives was observed for even thin-bituminous surfaced pavements. A suitable cost-efficient pavement section was chosen with reference to DSR, 2021. The study also attempts to design a geogrid-reinforced pavement section for a further reduced thickness of granular layers.