The undrained strength – liquidity index relationship

Abstract

A database of 641 fall cone tests on 101 soil samples from twelve countries has been analysed to determine the best mathematical relationship linking undrained shear strength with liquidity index. From the database, it is shown that the use of a linear relationship linking liquidity index and the logarithm of undrained shear strength that uses the commonly assumed 100-fold factor increase in strength from liquid to plastic limit over-predicts the measured data of soil strength. The use of a factor of about 35 for the ratio between the strength at liquid limit and that extrapolated to plastic limit is shown to be more realistic. Logarithmic liquidity index is examined and found to also correlate strongly with the logarithm of undrained shear strength, however it is shown that no great statistical improvement is present compared with the semilogarithmic formulation. When considering data of individual soils a power law fitting is shown statistically to be the preferred mathematical function.In this paper, it will be demonstrated, based on a large database, that the R MW value not only varies between soils but that an average value of around 35 is more appropriate, substantially less than the commonly assumed factor of 100. Fall cone strengths predicted from equation (2) will hence be un-conservative, 2013) The plastic limit of clays. Géotechnique, 63(6): 435-440. Hansbo, S. (1957) A new approach to the determination of the shear strength of clay by the fall cone test.

Discussion of “Water Content Ratio: An Effective Substitute for Liquidity Index for Prediction of Shear Strength of Clays” by Beshy Kuriakose, Benny Mathews Abraham, A. Sridharan & Babu T. Jose

“…(3a). The assumed ratio of undrained strength between liquid and plastic limit is calculated to be about 30.6 which is more comparable with the factor of 34.3 reported by Vardanega and Haigh (2014) than the commonly assumed factor of 100 (e.g., Schofield andWroth 1968 andWood 1990).…”

Use of fall cones to determine Atterberg limits: a review

“…4). However (as reviewed in the papers by O'Kelly (2013) and Vardanega & Haigh (2014b)), the data of Skempton & Northey (1952) show variations in the R MW value, which ranged between 70 and 160 for the four soils considered. Whyte (1982) suggested R MW % 70.…”

“…Whyte (1982) suggested R MW % 70. Vardanega & Haigh (2014b) demonstrated using a database of 101 soils that the ratio of computed undrained strengths from PL to LL was on average closer to 34·3 (when fall-cone undrained strength, s uFC , was fitted to I L ) and 83·5 (when s uFC was fitted to logarithmic liquidity index). Simply based on analysis of historical data, as the ratio of strengths at the PL and LL varies substantially between soils, these strength-based approaches can only coincidentally give correct PL values, actually measuring what might be termed the plastic strength limit (PL 100 ); that is the water content corresponding to s uFC ¼ 100 Â s uFC(LL) .…”

“…This assumes that cones having identical apex angle and surface roughness values are used in identifying both LL FC and PL 100 , and, furthermore, that the strain-rate dependency of the soil remains the same (as considered in the next section). Vardanega & Haigh (2014b) demonstrated from analysis of a large database of British standard (30°-80 g) fall-cone test results that, for any given soil, acceptable linear correlations could be drawn between both the logarithm of undrained strength and liquidity index and the logarithm of undrained strength and the logarithmic liquidity index. While the ratios of strengths at the PLs and LLs varied between soils, defining any two (or more) points on these linear relationships would give good predictions of undrained strengths at intermediate water contents (O'Kelly, 2013(O'Kelly, , 2016b).…”

Simple Methodology to Obtain Critical State Parameters of Remolded Clays Under Normally Consolidated Conditions Using the Fall-Cone Test

“…Some representative works have been published by Hansbo (1957), Karlsson (1961), Wood and Wroth (1978), Wood (1985), Leroueil and Le Bihan (1996), Koumoto and Houlsby (2001), Ayadat and Hanna (2007), Hazell (2008), Zentar et al (2009), Azadi and Monfared (2012), ClaveauMallet et al (2012), O'Kelly (2013), and Vardanega and Haigh (2014). The test has also been used to understand the postfailure behavior of soils regarding viscosity, allowing to study the creep-related phenomena (Budhu and Mahajan 2009;Cevikbilen and Budhu 2011;Boukpeti et al 2012) and, more recently, to study the applicability of time-displacement cone motion using an innovative inexpensive data-acquisition system for research and teaching purposes (Evans and Simpson 2015).…”