Element tests, such as water retention tests and triaxial tests, are efficient and widely used methods for investigating the elementary hydro-mechanical behavior of unsaturated soil. In recent research, discrepancies observed in unsaturated test results using axis-translation techniques (ATTs) with ceramic disks and microporous membrane filters (MM filters) have indicated that misunderstandings might be hiding behind the perceived elementary behavior seen in element tests. In this study, triaxial tests with ceramic disks and MM filters were firstly conducted on specimens of unsaturated completely decomposed granite sand, referred to as Masado in Japan, to compare the influence of different techniques on the test results. Then a soil–water-air coupled finite element-finite difference (FE-FD) method, based on a newly proposed unsaturated/saturated constitutive model coupled with a deformation-dependent water retention curve (WRC), was utilized to simulate triaxial tests as boundary value problems (BVPs) because of the non-uniform deformation of the specimens. Drained/vented triaxial tests showed that the stress–strain relation of Masado is basically the same regardless of the applied technique, while the amount of drainage discharge and degree of saturation during the shearing stage are quite different. The calculated average stress–strain relation basically reproduced a tendency similar to that of the tests. It was also shown from the calculation that the ATT with ceramic disks or MM filters significantly influences the distributions of saturation and stress within the specimens during shearing. It should be emphasized that unsaturated triaxial tests with the ATT are basically BVPs instead of so-called element tests.

保水试验和三轴试验等单元试验是研究非饱和土基本水力学行为的有效且广泛使用的方法。在最近的研究中，使用陶瓷盘和微孔膜过滤器（MM 过滤器）的轴平移技术（ATT）在不饱和测试结果中观察到的差异表明，元素测试中所观察到的基本行为背后可能隐藏着误解。本研究首先对日本Masado非饱和完全风化花岗岩砂试件进行陶瓷盘和MM过滤器三轴试验，比较不同技术对试验结果的影响。然后，采用土-水-空气耦合有限元有限差分（FE-FD）方法，基于新提出的非饱和/饱和本构模型以及变形相关保水曲线（WRC），模拟三轴试验：由于样本变形不均匀而导致的边值问题（BVP）。排水/排气三轴试验表明，无论采用哪种技术，Masado的应力应变关系基本相同，而剪切阶段的排水量和饱和度则有较大差异。计算出的平均应力-应变关系基本上再现了与测试相似的趋势。计算还表明，陶瓷盘或MM过滤器的ATT显着影响剪切过程中试样内饱和度和应力的分布。应该强调的是，ATT 的不饱和三轴试验基本上是 BVP，而不是所谓的单元试验。