Experimental and numerical investigation of coupled thermo-hydro-mechanical behaviour of clay with focus to cyclic processes

在许多岩土工程问题中，饱和或非饱和土会受到热-水-力(THM)耦合荷载的作用。此外，在一些重要的应用中，机械载荷、温度和湿度或吸力以循环方式变化。一个非常热门的例子是地热利用岩土结构，在可再生能源开发的背景下，这一情况正在增加。能量桩作为最突出的例子，受到机械载荷和热载荷的联合作用，后者由于环境温度的季节性变化而周期性变化。周围饱和或非饱和土体，尤其是粘土，在循环热荷载作用下，桩的承载力退化或沉降量增加的可能性还没有得到充分的研究。另一个例子是，全球气候变化导致环境温度的季节和每日变化较大，这也将影响岩土结构。像铁轨这样的基础设施会对地基土产生周期性的机械载荷，而土壤则会经历温度和水分的季节性变化。德国L嫩附近的一条铁路轨道大坝出现大裂缝，由细粒土壤组成，导致轨道关闭和精心修复，原因应该是近年来温度和湿度的更极端的季节性变化，以及来自过往列车的持续机械循环荷载。预计未来其他铁轨大坝的情况也会出现类似的恶化。尽管细粒土对各种岩土结构的设计具有实际意义，但在THM耦合荷载作用下，细粒土的复杂特性还没有得到充分的研究，因此还没有完全了解。这尤其适用于涉及机械载荷、温度和湿度的循环变化的过程。现有的本构模型主要局限于单调THM过程。因此，在拟议的研究项目中，计划对耦合THM载荷下的中塑性粘土进行彻底的试验研究，包括在波鸿鲁尔大学(RUB)或布拉格查尔斯大学(CUP)进行的固结仪和三轴试验。重点放在饱和和非饱和粘土在循环机械和热载荷下的行为。此外，还在橡胶上进行了温度循环的柱式实验，并测量了几个量(如温度、吸力、应力)沿高度的发展。基于实验结果，由RUB和CUP申请人建立的粘土本构模型将在描述复杂的THM加载路径方面得到改进。改进后的模型在单元试验和柱型试验的基础上进行了验证和比较，然后应用于数值模拟。

In many geotechnical problems either saturated or unsaturated soils are subjected to a coupled thermo-hydro-mechanical (THM) loading. Furthermore, in several important applications the mechanical loads, temperature and moisture or suction vary in a cyclic manner. A highly topical example is the geothermal use of geotechnical structures, which is increasing in the context of renewable energy development. Energy piles as the most prominent example are subjected to a combined mechanical and thermal loading, with the latter one varying cyclically due to the seasonal changes of the ambient temperature. The possible degradation of the pile capacity or settlement increase due to the cyclic thermal loading of the surrounding saturated or unsaturated soil, in particular in case of clay, has not been sufficiently investigated yet. As another example, the global climate change leads to larger seasonal and daily variations of ambient temperature, which will also affect geotechnical structures. Infrastructure like railway tracks induce a cyclic mechanical loading to the subsoil, while the soil undergoes seasonal changes of temperature and moisture. The development of large cracks at a dam of a railway track near Lünen, Germany, composed of fine-grained soil, leading to closure of the track and an elaborate restoration, is supposed to be caused by the more extreme seasonal changes of temperature and moisture during recent years, in combination with the continued mechanical cyclic loading from the passing trains. A similar deterioration of other dams of railway tracks can be expected for the future. Despite its practical relevance for the design of various geotechnical structures the complex behaviour of fine-grained soils under coupled THM loading has not been sufficiently investigated and is thus not fully understood yet. This applies in particular to processes involving a cyclic variation of the mechanical load, temperature and moisture. The available constitutive models are mainly restricted to monotonic THM processes. Therefore, a thorough experimental investigation of a medium-plastic clay under coupled THM loading is planned in the proposed research project, including oedometer and triaxial tests performed at either Ruhr-University Bochum (RUB) or Charles University, Prague (CUP). The focus is laid on the behaviour of both saturated and unsaturated clay under cyclic mechanical and thermal loading. Furthermore, column-type experiments with temperature cycles and a measurement of the development of several quantities (e.g. temperature, suction, stress) along the height are conducted at RUB. Based on the experimental results constitutive models for clay developed by the applicants of both RUB and CUP will be enhanced with respect to the description of complex THM loading paths. The enhanced models are validated and compared based on the element tests and column-type experiments, before being applied in numerical simulations.