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，无论是饱和土还是非饱和土都受到热-水-力耦合作用。此外，在一些重要的应用中，机械负载、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岩土结构的地热利用，这在可再生能源开发的背景下正在增加。作为最突出的例子，能量桩受到机械和热负荷的组合，后者由于环境温度的季节性变化而周期性变化。由于周围饱和或非饱和土壤的循环热负荷，特别是在粘土的情况下，可能的退化的桩容量或沉降增加尚未得到充分的研究。另一个例子是，全球气候变化导致环境温度的季节和日变化较大，这也将影响岩土结构。铁路轨道等基础设施会对底土产生循环机械载荷，而土壤会经历温度和湿度的季节性变化。德国吕嫩附近一条铁路轨道的大坝出现大裂缝，由细粒土组成，导致轨道关闭和精心修复，据推测，这是由于近年来温度和湿度的极端季节性变化以及来自过往列车的持续机械循环载荷造成的。预计未来其他铁路堤坝也会出现类似的恶化。尽管它的实际相关性的各种岩土结构的设计，耦合THM荷载下的细粒土的复杂行为还没有得到充分的研究，因此还没有完全理解。这尤其适用于涉及机械负载、温度和湿度的周期性变化的过程。现有的本构模型主要局限于单调的THM过程。因此，在拟议的研究项目中，计划在耦合THM荷载下对中塑性粘土进行彻底的实验研究，包括在鲁尔大学波鸿（RUB）或查尔斯大学布拉格（CUP）进行的固结仪和三轴试验。重点放在饱和和非饱和粘土循环机械和热负荷下的行为。此外，在RUB进行了具有温度循环的柱型实验和沿着高度的几个量（例如温度、吸力、应力）的发展的测量。基于实验结果，将增强由RUB和CUP的申请人开发的粘土本构模型，以描述复杂的THM加载路径。通过单元试验和柱型试验对改进模型进行了验证和比较，并将其应用于数值模拟。

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.