Soil Behavior and Characterization: Effect of Improvement in CBR Characteristics of Soil Subgrade on Design of Bituminous Pavements

The California bearing ratio (CBR) value greatly influences the strength characteristics of soil subgrade, hence, is an important parameter to understand the soil behavior pertinent to pavement design. The CBR value, along with the empirical curves, is used to determine the thickness of a pavement and its component layers, thus aiding in the design of flexible pavements. If the naturally occurring local soil subgrade has low strength in terms of CBR and poor engineering properties, improved soil subgrade has to be provided by way of lime/cement treatment or by mixing locally available cheap alternative materials or by mechanical stabilization and other similar techniques. In the present study, an attempt has been made to review the soil behavior in terms of CBR characteristics for two methods of soil properties enhancement, viz. addition of lime and rice husk ash to soil and the method of improvement of soil subgrade overlain by compacted fly ash with geotextile at soil–fly ash interface. Using the data obtained from the review study, design of a bituminous pavement with granular base and sub-base layers and an alternative pavement with RAP layer with CTSB sub-base have also been attempted using the IRC 37:2018 guidelines and IITPAVE software to find out the adequacy of the two subgrade improvement methods with respect to reduction in pavement thicknesses. Further, some design charts have also been developed for the stabilized soil subgrades for traffic intensities of 5, 15, 30, 50, 80 and 100 msa for both pavement types.