Viscous ISA Modell for clays under cyclic and monotonic loading

循环单调荷载下粘土的粘性 ISA 模型

• 批准号: 324517837
• 负责人: Professor Dr.-Ing. Theodoros Triantafyllidis
• 金额: --
• 依托单位: Lehrstuhl für Bodenmechanik, Grundbau u Umweltgeotechnik
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2016
• 资助国家: 德国
• 起止时间: 2015-12-31 至 2023-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/324517837?language=en
• 关键词: Viscous; ISA; Modell; clays; under

The stress-strain behavior of soft clayey soils is governed by their viscosity. Viscosity is the main cause for the time-dependend behavior of soft clays, which is of great importance for the evaluation of long-term performance of foundation structures or soil-structure interactions in geotechnical engineering problems. Phenomena like creep, relaxation and rate dependence are the main causes for e.g. subsequent tilt or settlement of structures built on soft clayey soils or earth slides. Considering the important consequences of time-dependent phenomena, some viscous models have been developed in the past. The visco-hypoplastic model assumes the equivalence between the viscous strain rate and plastic strain rate so that only one is considered in the model. Hence it leads to an over-estimation of the peak of the shear stress. The most important drawback of these models is that they lack on simulating the accumulation of the plastic strain and/or the pore water pressure build up, which has fatal consequences for the soil behavior under cyclic loading.The Modified Cam Clay model has been as well adopted to account for viscous phenomena named as UH model. This model is not able to describe relaxation or creep after unloading, because the constitutive model shows elastic behavior after unloading.Therefore, the primary task of this project will be to develope a model within the ISA platform suitable for clays, which should be extended to account for time-dependent phenomena without loosing the possibility to describe time-independent behavior as a feature of the same model. Moreover the proposed model should describe well the cyclic behavior of viscous clayey soils for different stress/strain amplitudes. For this purpose, a new state variable accounting for the number of cycles the soil has been experienced will be introduced. Thus, the historical elements of the soil will be included in the constitutive model. Finally, the extended model will be calibrated for different loading speeds in laboratory tests conducted on Kaolin and Lower Rhine Clay, which will provide an information about the time-dependent behavior of clays in general as well as about their behavior under cyclic loading.

软粘土的应力-应变特性受其粘性的控制。粘性是软粘土时变特性的主要原因，这对于评价地基结构的长期性能或土-结构相互作用等岩土工程问题具有重要意义。蠕变、松弛和速率相关性等现象是导致软粘土上建造的结构物随后倾斜或沉降或滑坡的主要原因。考虑到时间相关现象的重要后果，过去已经开发了一些粘性模型。 粘亚塑性模型假定粘塑性应变率和塑性应变率相等，因此模型中只考虑其中一个。因此，这导致对剪切应力峰值的高估。这些模型最大的缺点是不能模拟循环荷载作用下土体的塑性应变和孔隙水压力的累积，而塑性应变和孔隙水压力的累积对土体的循环特性有着重要的影响。该模型不能描述卸载后的松弛或蠕变，因为本构模型在卸载后表现出弹性行为。因此，本项目的主要任务是在伊萨平台内开发一个适用于粘土的模型，该模型应扩展到考虑时间相关现象，同时不失去描述时间无关行为的可能性，作为同一模型的一个特征。此外，所提出的模型应该很好地描述粘性粘土的循环行为，不同的应力/应变幅。为此，将引入一个新的状态变量，说明土壤经历的循环次数。因此，土的历史元素将包括在本构模型中。最后，将在高岭土和下莱茵河粘土上进行的实验室试验中，针对不同的加载速度校准扩展模型，这将提供关于粘土的一般时间依赖性行为以及循环加载下的行为的信息。