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

迄今为止，在处理部分饱和土的力学行为时，如何描述土-水相互作用（吸力）的影响仍在讨论中。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。越来越多的室内试验表明，有效应力的概念是足够的，以描述从土-水相互作用的宏观影响时，处理极限状态，如抗剪强度相关的问题。然而，考虑到完整的机械应力和吸力范围以及不同的故障模式，系统的实验验证仍然缺失。因此，该项目的目的是实验验证有效应力的概念与部分饱和土壤的抗剪强度。将使用细粒土样品进行不同类型的剪切试验（三轴、直接剪切、含水量和吸力控制试验）和拉伸试验（直接和空心圆柱体）。与现有工程不同，拟议的实验研究考虑了拉伸和低至高机械应力以及干燥至饱和条件，因此考虑了整个吸力范围。此外，对不同类型测试的结果进行比较可以研究不同失效模式可能产生的差异。试验结果将用于推导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.