Experimental Validation of Effective Stress Concept in Partially Saturated Soils; Suction, Shear Strength and Tensile Strength

到目前为止，在处理部分饱和土壤的力学行为时，如何描述土壤水相互作用(吸力)的影响仍在进行中。一种方法是用有效应力来描述吸力的宏观效应。这种方法的基本优点是经典的土力学原理可以应用于部分饱和土体。越来越多的室内试验表明，有效应力概念足以描述土水相互作用在处理极限状态时的宏观效应，例如与抗剪强度有关的问题。然而，考虑到完整的机械应力和吸力范围以及不同的失效模式的系统实验验证仍然缺乏。因此，该项目的目的是通过实验验证关于部分饱和土抗剪强度的有效应力概念。将使用细粒土样进行不同类型的剪切试验(三轴、直剪、含水率和吸力控制试验)和拉伸试验(直接和中空圆柱体)。与现有工程不同，拟议的实验研究考虑了拉伸、低到高的机械应力以及干燥到饱和的条件，因此考虑了整个吸力范围。此外，通过比较不同类型测试的结果，可以调查不同故障模式可能导致的差异。试验结果将被用来推导出封闭形式的有效应力方程，该方程描述了部分饱和土壤的抗剪强度作为吸力、饱和度和土壤结构参数的函数。

To date there is an ongoing discussion how to describe the effect of soil water interaction (in terms of suction) when dealing with the mechanical behavior of partially saturated soils. One approach is to describe the macroscopic effect of suction in terms of effective stress. This approach has the fundamental advantage that classical soil mechanic principles can be applied to partially saturated soils. A growing number of lab tests indicates that the effective stress concept is sufficient to describe macroscopic effects from soil water interaction when dealing with limit state e.g. shear strength related problems. However a systematic experimental validation taking into account the full mechanical stress and suction range as well as different failure modes is still missing. Thus the purpose of the project is to experimentally validate the effective stress concept with respect to shear strength of partially saturated soils. Different kinds of shear tests (triaxial, direct shear, water content and suction controlled tests) and tensile tests (direct and hollow-cylinder) using fine grained soil samples will be performed. Unlike existing works the proposed experimental study takes into account tensile and low to high mechanical stresses as well as dry to saturated conditions and therefore the full suction range. In addition comparison of the results from the different kinds of tests allow to investigate possible differences resulting from different failure modes. Test results will be used to derive closed form effective stress equations describing the shear strength of partially saturated soils as a function of suction, saturation and soil structure parameters.