TU Berlin

Chair of Water Resources Management and Modeling of HydrosystemsAbstract

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Abstract

Land subsidence is a complex phenomenon which occurs all around the world. The study and understanding of the phenomenon, its causes and effects, the processes, such as flow, deformation and fracturing are very important in a spectrum of approaches for predicting the consequences and future damages. Meanwhile, numerical simulation is an important and powerful tool to analyse land subsidence and predict the impact of changing conditions. It also serves to understand new processes if the conditions will change. The economical damages caused by land subsidence have brought large monetary losses to cities all around the world. In modern times cities have grown rapidly and likewise have the agricultural and industrial activities. In order to satisfy the new demands for the vital liquid, for which the surface water bodies have not been sufficient, subterranean water has had to be exploited to such an extent that its extraction has outreached groundwater recharge. The main objective of this research is to deeply analyse the principal conditions, associated hazards, parameters and processes that play an important role in the land subsidence phenomenon using numerical simulation. The present work contains several innovations dealing with advances in model concepts in order to investigate land subsidence processes, fracture formation as well as flow and deformation through fractured soils. The present work analysed the flow and soil deformation behaviour due to fast water infiltration and water extraction in faulted aquifers through numerical modeling. For the flow a two-phase flow model and for the deformation elasto-plastic models, the Mohr-Coulomb model and the Hardening Soil model, were applied and weakly coupled. Three examples of numerical modeling of two-phase flow as well as soil deformation are presented. The first application is a model of infiltration through a single-layer system. Here the influence of the inclination of the fracture and the inclination of the surface were investigated as well as the soil’s deformation. The second application examined a two-layered system consisting of a stratum with low permeability on its surface and a fracture that allows rapid water flow through the impermeable stratum to the lower stratum with higher permeability. A model concept for fracturing mechanism was also proposed. The third application describes a model concept for fracturing mechanism after groundwater extraction through a well near a highly permeable pre-existing fault. An important finding was to show that not only an inclined fault zone with low permeability could act as a hydrological barrier for the water flow in an aquifer but also an inclined fault zone with high permeability. Also the results show that this barrier effect could be a factor for triggering land subsidence. Another important result of this research was the development of a conceptual model of a mechanism for the generation of fracturing and triggering of land subsidence: fast rain water infiltration through fault zones.

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