Fall-cone penetration and water content relationship of clays

Abstract

Results of previous studies on using the fall-cone test to determine the plastic limit of soils show that further research is warranted. The present investigation devotes itself to modification of the specimen preparation technique, examination of the relationship between depth of cone penetration and water content, and estimation of the plastic limit using the penetration depth against water content relationship. Specimen rings are made and used to replace the specimen cup so as to facilitate the preparation of specimens. Data of 26 soils, covering a wide range of liquid limits from 30% to 526%, show that the logarithm of depth of cone penetration against logarithm of water content relationship is linear. Therefore, a linear equation with two soil-dependent parameters is developed for estimation of the plastic limit. For a soil, the value of the soil-dependent parameters can be determined from as little as four fall-cone tests and substituted into the equation to estimate the plastic limit. The computed plastic limits of the soils analysed are within 0·8–1·2, with an average value of 1, times the measured plastic limits. The effects of strain rate and undrained strength ratio on the estimation of the plastic limit are evaluated and found to be limited.