Evaluation of Penetration Index of Untreated and Treated Soil Using Dynamic Cone Penetrometer

Small-scale dynamic cone penetrometer is a rapid and less expensive tool extensively used for assessment of strength of soil layers to a limited depth of highway and airfield pavements. Penetrometer consists of a cone of 20 mm diameter with 60º apex angle driven into the soil by a hammer of weight 8 kg falling freely through a height of 575 mm, and tests are conducted by compacting soil in calibration cylinders of two different sizes. Tests are conducted on untreated, cement or lime treated clay of high compressibility and clayey sand mixed with 5–30% moisture content and compaction energy per unit volume of layer ranged from 0.5 to 6 kg/cm2. Penetration index of untreated and treated clay of high compressibility is varied from 5 to 42 mm/blow, and unconfined compressive strength is ranged from 101 to 233 kPa. Unconfined compressive strength, California bearing ratio and penetration index are presented in charts for different moisture content and degree of compaction. The average penetration index decreased with increase of lime or cement content and increase of curing period.