Development of correction factor for penetration index of dynamic cone penetrometer to assess in situ soaked California bearing ratio

摘要

CBR value of the soil is an important parameter to design a new pavement crust and to estimate the requirement of overlay thickness for strengthening or upgrading an existing road. Laboratory CBR at 97% of modified maximum dry density at worst anticipated moisture is determined when the subgrade is to be laid from borrow pits or existing subgrade is to be loosened and recompacted. When an existing embankment layer or subgrade is to be used in its natural condition for upgrading the class of a highway, determination of CBR at worst moisture content at in situ density is required and is a cumbersome process. In this study, 33 soils samples consisting of natural alluvial soil from in situ subgrade and embankment were tested for CBR at different densities and moisture contents. Index properties along with resistance to the penetration of dynamic cone penetrometer were also measured at similar conditions on the field layers. The data was analysed using statistical software SPSS and Microsoft Excel to develop two different equations to find the correction factors based upon field moisture content (MC_(Fieid)) and plasticity index value of the soil and relative compaction of the subgrade/embankment layer. The results are validated on another project having parameters within the range of the soils tested during the study.