Microscopic investigation on the physical and mechanical meanings of liquid limit tests on clayy soils.

液体极限定义为土壤不再像液体一样容易流动并变成塑性的水分含量。这两种可供选择的液体限度试验一般都是标准化的。一种是在日本和美国流行的卡萨格朗德测试，另一种是在欧洲推广的落锥测试。本研究以两种典型粘土矿物蒙脱石(M)和高岭石(K)为研究对象，对两种测试方法的力学特性进行了实验研究，并从微观角度探讨了两种测试方法在粘土-水体系中的物理意义。在K=100%样本的情况下，两种试验的LL值几乎一致为30.2%。与蒙脱石含量成正比，粘土样品表现出流动性，其LL值呈线性增加。然而，他们之间增加的程度不同。在极端情况下，M=100%的样品从Casagrande试验中获得了895%，从落锥试验中获得了552%的样品。这一差异被证明是由于两种试验的物理过程的不同以及蒙脱石粘土的触变性造成的。同样的样品也用简单的测力计测量了抗拉强度。他们表现出与LL测试基本相同的趋势，在LL状态下，他们的抗拉强度被评估为20-50kpa。

Liquid limit (LL) is defined as the water content in which the soil ceases to flow easily like a liquid and becomes plastic. The two alternative liquid limit tests are standardized in general. One is the Casagrande test which is popular in Japan and the U.S.A., and the other is the fall cone test spread in Europe. The purpose of this study is to experimentally examine the mechanical characteristics of both two tests and investigate their physical meanings from microscopic view point on clay-water system.Two typical clay minerals ; montmorillonite (M) and kaolinite (K) were adopted and their mixture samples were tested according to both standards. In case of K=100% sample, LL values from both tests almost agreed as 30.2%. In proportion to the montmorillonite content, clay samples exhibited a fluidity and their LL values increased linearly. However, increasing degrees were different between them. At the extreme, M=100% sample took 895% from the Casagrande test, while 552% from the fall cone test.This discrepancy proved to result from the differences in physical procedures of both tests and from thixotropic properties of montmorillonite clay. Tensile strengths were also measured for the same samples with the use of simple force gauge. They expressed substantially the same tendency with LL tests and their tensile strengths were evaluated as 20-50 kPa in the state of LL.