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.

中文翻译：

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锥形法测定粘土的液体和塑料极限

根据几位研究人员的研究，在液体极限水分含量下，土壤的不排水剪切强度可以认为约为1.7 kPa。一种方法将土壤的可塑性指数定义为在不排水的抗剪强度中产生100倍变化的含水量范围。这导致重新定义了塑性极限，即不排水剪切强度为170 kPa时的含水量。在对数-对数图中，从塑性极限附近到液体极限附近的宽范围水含量中，不排水的剪切强度与水含量的关系被发现是线性的。通过对数-对数图对不排水的剪切强度与水含量的关系进行归一化，得出以下结论：通过圆锥渗透获得的液体极限和塑性极限处的水分，也可能是唯一相关的。这与对Atterberg极限的最初理解相矛盾，即液体极限和塑料极限是根本不相关的两个独立参数。从锥法将此塑性极限值称为PL更合适_100，以区别于Casagrande的塑料极限。