COMPUTATION OF PLASTIC LIMIT USING MATHEMATICAL MODEL

This paper presents a mathematical model that uses a British cone to predict the soil moisture-penetration relationship. This relationship is nonlinear for non-bentonite bearing soil and can be modelled using a sigmoidal mathematical function. The developed mathematical model gives a unique opportunity for computing and predicting the fall cone penetration of the soil even at a very low moisture content, at which, due to practical limitations, it is impossible to determine the soil penetration. The mathematical model was found to fit the moisture-penetration data reasonably well. Based on the data presented in this paper, both the liquid limit and plastic limit can be determined from the extended liquid limit flow curve by determining the plastic limit at a 1.2 mm penetration value. The computed plastic limit at a 1.2 mm penetration value was found to be in close agreement with the measured plastic limit.

本文提出了一种以英国落锥（British cone）为测试工具的数学模型，用于预测土壤含水率与贯入度之间的关系。对于不含膨润土的土壤，该关系呈非线性特征，可采用S型（sigmoidal）数学函数进行建模。所构建的数学模型为计算、预测土壤落锥贯入度提供了全新的可行途径，即便在极低含水率条件下亦是如此——此类工况受实际操作限制，无法直接测定土壤贯入度。经检验，该数学模型可较好地拟合含水率-贯入度实测数据。基于本文提供的试验数据，可通过延伸液限流动曲线，以贯入度1.2mm为判定基准确定塑限，进而同步得到液限与塑限。经计算得到的贯入度为1.2mm时的塑限值，与实测塑限值具有高度一致性。