Liquid and plastic limits of clays by cone method

Binu Sharma,A Sridharan

doi:10.1186/s40703-018-0092-0

Binu Sharma, A Sridharan

Open Access

https://doi.org/10.1186/s40703-018-0092-0

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Abstract

Undrained shear strength of a soil at the liquid limit water content can be considered to be around 1.7 kPa according to several researchers. Plasticity index of soils has been defined by one school of thought as a range of water content producing a 100-fold variation in their undrained shear strength. This has led to the redefinition of the plastic limit as the water content at which undrained shear strength is 170 kPa. The undrained shear strength-water content relationship has been found to be linear in the log–log plot for a wide range of water contents beginning from around the plastic limit to near the liquid limit. Normalization of undrained shear strength—water content relationship in a log–log plot has led to the conclusion that the water content at the liquid limit and at the plastic limit, obtained by cone penetration, could also be uniquely related. This contradicts the original understanding of Atterberg limits, namely liquid and plastic limits which are two independent parameter not related at all. It is more suitable to call this value of plastic limit from cone method as PL100 to differentiate it from Casagrande’s plastic limit.

Highlights

Undrained shear strength of a soil from water content around the liquid limit to water content around the plastic limit can be determined by the fall cone test
The undrained shear strengths of 43 inorganic soil samples were determined by the Swedish fall cone test, the liquid limit of which varied from 33.8 to 82%
Wroth and Wood [26], and Belvisco et al [2], suggested that the logarithmic depth of penetration against water content relationship is linear between the liquid limit and the plastic limit

Summary

Introduction

Undrained shear strength of a soil from water content around the liquid limit to water content around the plastic limit can be determined by the fall cone test. Determination of liquid limit by the fall cone test is based on the premise that soil assumes a unique state at the liquid limit yielding a unique shear strength. Many research workers have attempted to show that this unique shear strength at the liquid limit bears a definite relationship with that at the plastic limit [2, 8, 13, 16, 25, 26]. According to several researchers ([10, 12, 15, 23, 26] to name a few), undrained shear strength at the liquid limit water content can be considered to be unique (without much loss of accuracy) for all soils.

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