Fall-cone penetration and water content relationship of clays

Results of previous studies on using the fall-cone test to determine the pl astic limit of soils show that further research is warranted. The present i nvestigation devotes itself to modification of the specimen preparation tec hnique, examination of the relationship between depth of cone penetration a nd 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 specime ns. Data of 26 soils, covering a wide range of liquid limits from 30% to 52 6%, 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 li mit. For a soil, the value of the soil-dependent parameters can be determin ed 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 an alysed are within 0.8-1.2, with an average value of 1, times the measured p lastic limits. The effects of strain rate and undrained strength ratio on t he estimation of the plastic Limit are evaluated and found to be limited.