Research On Virtual Reality Technology In Land Subsidence Simulation

Land subsidence is a delayed geological disaster, which attracts more attention because of its wide influences and severe consequences. The Yangtze River delta is one of areas occurring serious land subsidence in China. While Suxichang area is in the middle of Yangtze River delta, in which land subsidence is induced by overpumping groundwater continuously. Many institutes have carried out a lot of researches, such as investigation and evaluation of this geological disaster, analysis of the geological and environmental conditions that induce the land subsidence, the mechanism of subsidence, and so on. Though, fruitful results have been achieved. The expressions of these results are normally text, two-dimensional graphs or profiles. Although these can supply a theoretical basis for geological workers or decision makers to correctly learn current situations of land subsidence and enact proper countermeasure of land subsidence control measures, they still have some shortages as follows.â‘ Three-dimensional dynamic expression of land subsidence has not been realized.â‘¡Mutual relation between land subsidence and diversified factors has not been directly visually expressed.â‘¢Forecasts of land subsidence are difficult to make, namely, they are unpractical. Virtual Reality Technology (VRT) is a potent new tool to resolve these problems mentioned above. It utilizes computer technology to simulate the real world or imaginary environment, in which researchers can roam naturally and operate virtual objects in an interactive means. On account of the above understanding, the paper is unfolded from the following parts:Firstly, according to the present problems exiting in expression ways of land subsidence achievement and combining the current situation and tendency of reach upon VRT, this technology is used to simulate process of land subsidence. The carrying out research not only broadens the scope of the application of virtual reality technology, but also provides a virtual platform to analyze subsidence mechanism.Secondly, the main study contents are determined and the related technology route is developed. Virtual module, developing mode and physical configuration of the land subsidence virtual reality system are designed. Taking into account of the strong VC + + interface developmental functions and the graphics visualization functions of OpenGL, VC++ and OpenGL are adopted as a developing-mode of Virtual reality. During the course of the study, vividly simulate the occurrence and development process of land subsidence is the emphasis. Because 3D hydro-geological structure is the material of occurring land subsidence, groundwater level is the main affecting factor and ground fissures are induced consequences of land subsidence, 3D hydro-geological structure, groundwater surface and ground fissures land subsidence should be expressed when land subsidence is simulated. So the land subsidence virtual reality system includes three modules of 3D hydro-geological structure, groundwater surface and land subsidence. Then the function of each module is described in detail. At the same time the format and table name of data source to build model and producing model data are regulated respectively, when they are stored into SQL database.Thirdly, elaborate discussion is given to data preparation, modeling process, the principal arithmetic and interactive operations of the virtual 3D hydro-geological structure, groundwater surface, land subsidence and its inducing consequence, respectively. In the course of studying, 3D hydro-geological model, which is the basis of virtual groundwater surface module and land subsidence model, is constructed by hybrid modeling algorithm. All of three items are exhibited by Triangulated Irregular Network and locations of the three Triangulated Irregular Network models projected on the plan are the same. However, the representing attributes of triangle vertexes of the three Triangulated Irregular Network models are stratum elevation, groundwater level and stratum elevation after land subsidence, respectively.Virtual 3D hydro-geological structure: Researchers are able to learn spatial distribution and mutual relationship of stratum of 3D hydro-geological structure from various manners. Besides, attribute information in arbitrary position of this model can be got by the tool of information inquiry.Virtual groundwater surface: Groundwater surface virtual model is built based on 3D hydro-geological model. Researchers can learn undulation of groundwater surface in Suxichang area and learn hydro-geological attributions on the surface by using information inquiry. Meanwhile, a new method-cutting by equivalence plane method, used to generate groundwater contours, is discussed.Virtual land subsidence: The process of land subsidence is virtually expressed. Due to the rate of land subsidence is the largest in the west of Wuxi city, land subsidence process of each stratum is simulated in this area. The dynamic process can be observed by kinds of styles. At the same time, the correlation model between groundwater level and accumulative land subsidence is built, by which the value of accumulative land subsidence can be calculated when the groundwater level is given. Function of forecasting land subsidence is realized.Virtual ground fissures: Adopting polygon cutting surface moedel to construct ground cracks and using dynamic texture binding technology to simulate the fissures of house wall, the whole process of ground fissures are simulated. Researcher can understand this process from random point of view.Finally, Mechanism of land subsidence and ground fissures are analyzed. From the dynamic process of groundwater level and land subsidence, it can be directly obtained that land subsidence has a close relevance with groundwater level. That is the lower dewatered groundwater level is, the bigger of the value of land subsidence is. What is more, it can be discerned from the virtually dynamic process that land subsidence is not only the result of consolidation of aquitard but also releasing a certain amount of water of aquifer. Meanwhile, by comparing the spatial distribution of ground fissure, bedrock surface shape, the distribution of groundwater and cumulative sediment, it is known that in the west of Wuxi, the ground cracks generated in which the accumulative value of land subsidence is about 1000mm, the groundwater level is about 70 meters and the slope of rising part of bedrock surface is bigger.