Study On Formation Mechanism And Numerical Simulation Of Land Subsidence In Xi'an

Land subsidence is one kind of complex environmental and geological problems which has attracted attention from home and abroad. It is a phenomenon that regional ground elevation is lowered by the compression and deformation of soil mass in the veneer of crust under both natural and man-made factors. It is a slow onset disasters, which is difficult for people to detect. And it is also has many characteristics, such as long duration, wide range of influence, complex genetic mechanisms, difficult to control, easy onset, progressive, irreversible, etc. So the land subsidence has been threatening people's life, socio-economic and sustainable development seriously. There has been serious land subsidence in Xi'an, which is one of the four famous ancient capitals of the world, since the 70s of last century, Xi'an area suffered enormous economic losses due to the land subsidence. Therefore, it has very far-reaching significance to study the law and mechanism of the development of land subsidence for both people's life and the economic sustainable development.This paper describes the geological background of Xi'an area, with which as a prerequi-site, firstly, it discusses the development process of land subsidence in Xi'an in detail, pointing at that excessive pumping of groundwater is the main reason for land subsidence.Secondly, based on the comprehensive consideration of natural factors and human facto-rs, mechanism of the land subsidence in Xi'an is analyzed in-depth. As follows:(1) Natural Factors The paper analyzes from some aspects, such as regional tectonics, earthquakes, soil weight, collapsible loess, and so on. From which we came to the conclusion that natural factors are not the dominant factor of land subsidence in Xi'an area.(2) Human Factors In this part, the paper studies from both pumping pressure deep underground water and urban construction's influences. This article focused on the mechanism of the deep confined aquifer's vertical displacement and horizontal deformation, which is caused by pumping. And it also explained the formation mechanism of the ground subsidence conical depression. In the final part of this section, the author indicates that modern urban construction can not be ignored for impacting on land subsidence.In Chapter V, on the basis of the Biot consolidation theory, the paper selects the land subsidence which is near the Geological Technical School in Xi'an city, and uses FLAC2D software to make two-dimensional numerical simulation and soil-seepage coupling calcula-tion. By analyzing the simulation results, the author finds that the simulation results are generally consistent with the monitoring results. On the one hand, it shows that the analysis of the characteristics and mechanism of ground's vertical settlement and horizontal displacement is correct. On the other hand, it confirms the rationality and correctness of the numerical simulation model and the code orders.Some conclusions and proposals are put forward in the end of this paper, which is combined with the current study on the land subsidence.