Time-dependent load-deformation behaviour of foundations under alternating loads in overconsolidated clay

在现有建筑物的现代化和复兴背景下，必须解决日益复杂的任务，例如地基的再利用，特别是在城市地区。如果要将现有基础和新基础结合起来，则对现有基础的荷载-沉降特性进行准确预测尤为重要。为了能够通过将现有基础与新结构相结合来开发进一步的优化潜力，因此还必须在更大程度上考虑基础的随时间变化的变形行为。这就对地基土的建模提出了很高的要求，因为对于粘性土，固结过程和随时间变化的材料特性（蠕变）都需要进行现实的评估。除了随时间变化的土壤变形特性以及拆除和重建阶段产生的不断变化的结构载荷外，附近的建筑工程也会影响地基的长期变形特性。特别是邻近地下水位的下降和地下水位的相关变化是造成城市地区地基暴露于由土壤中的隆起和有效应力变化引起的交变荷载的原因。拟议研究项目的重点将是在超固结粘土中的筏基和桩筏的长期变形特性。在美因河畔法兰克福的地基上进行的测量持续了几十年。此外，离心模型试验和耦合孔隙压力-位移有限元分析的计划，与时间相关的材料行为的土壤被代表使用粘次塑性材料模型。本项目的目的是研究承受交变荷载的地基的承载性能，并定性和定量地评估考虑固结和蠕变对长期性能的影响。具体而言，将讨论以下主题：-交变荷载如何影响地基的蠕变变形。-在随后的加载阶段，蠕变变形在多大程度上影响基础刚度。筏基和桩筏是否表现出不同的时间沉降特性？在桩筏的情况下，交变荷载、固结和徐变如何影响桩和筏之间的荷载分布？交变荷载、固结和徐变如何影响工程实践中常用的设计参数，即地基反力模量和等效桩弹簧刚度。

In the context of the modernisation and revitalisation of existing buildings, increasingly complex tasks such as the re-use of foundations, have to be addressed, especially in urban areas. An accurate prediction of the load-settlement behaviour of existing foundations is of particular importance if existing and new foundations are to be combined. In order to be able to exploit further optimisation potential by coupling existing foundations with new structures, the time-dependent deformation behaviour of foundations must therefore also be taken into account to a greater extent. This poses high demands on the modelling of the subsoil, since for cohesive soils both consolidation processes and the time-dependent material behaviour (creep) need to be realistically assessed.In addition to the time-dependent deformation behaviour of the soil and changing structural loads arising from demolition and reconstruction phases, construction works in the vicinity also influence the long-term deformation behaviour of foundations. In particular, neighbouring groundwater lower-ings and the associated changes in the groundwater level are responsible for the fact that foundations in urban areas are exposed to alternating loads resulting from changes in uplift and effective stresses in the soil.The focus of the proposed research project will be on the long-term deformation behaviour of raft foundations and piled rafts in overconsolidated clay, with measurements on foundations in Frankfurt am Main extending over several decades to be employed. In addition, centrifuge model tests and coupled pore pressure-displacement finite element analysis are planned, with the time-dependent material behaviour of the soil being represented using visco-hypoplastic material models. It is the aim of this project to investigate the load-bearing behaviour of foundations subjected to alternating loads and to qualitatively and quantitatively assess the effects on the long-term behaviour considering consolidation and creep.In detail, the following topics are to be addressed:- How do alternating loads affect the creep deformations of foundations.- To what extent do creep deformations influence the foundation stiffness during subsequent load-ing phases.- Do raft foundations and piled rafts show different time-settlement behaviour- How do alternating loads, consolidation and creep affect the load distribution between piles and rafts in the case of piled rafts.- How do alternating loads, consolidation and creep affect the design parameters commonly used in engineering practice, namely modulus of subgrade reaction and equivalent pile spring stiffness.