Numerical Simulation Of Land Subsidence Considering Both Effects Of Load And Groundwater Exploitation And Applications

With the fast economic development, the groundwater exploration might be over exploited to some extent, especially at the developed cities in the coast region in China. In the some soft soil areas, except over exploitation of groundwater, load over the land surface is also one of the main factors for land subsidence, such as the buildings. Land subsidence, as a geological environment, has caused the attention of the governments and scientists several decades ago. Regardless of the mechanism, monitor or predict of the land subsidence, the research has been very deeply conducted. However, as for the numerical simulation of land subsidence in the past, concerns mainly only focused on the influence of groundwater exploitation problem, not load. Actually, the load is one of the main factors for the land subsidence. By carefully reviewing the literature, we found that there were still many problems needed to be studied, which are listed as follows.(1) In the existing studies of land subsidence, most of them focused on groundwater exploitation as the factor for land subsidence. In fact, the construction works of the load land subsidence caused by the proportion of urban development with the construction of more and more significant. Therefore, it is necessary to carry out the research on the mechanism of theoretical methods and groundwater exploitation both load factors, and the numerical simulation. In this study, we will establish the land subsidence numerical model of Ningbo basins to consider both load and pumping factors.(2) The consolidation will result in changes in the soil parameters, parameters in the most studies assumed to be constant, which cannot reflect the reality. Therefore, the land subsidence studies, combined with the actual study area, it is necessary to establish the parameters of the model.(3) The soil stress-strain models usually are based on the elastic model, but the actual stress-strain characteristics of the soil is very complex. Combined with the actual study area, it is very meaningful to establish realistic constitutive model for improving the land subsidence model simulation.(4) There is no consideration of load land subsidence and groundwater extraction simulation software, developed in line with the mechanism to facilitate consideration of the applicable groundwater extraction and land subsidence simulation software loads for research is very helpful.Based on the consideration of these issues, this study will take Ningbo Plain as an example, and consider the groundwater exploitation and loads of land subsidence mathematical models and numerical simulation studies, the establishment of land subsidence mathematical models and numerical models of the study area, predicted under different conditions land subsidence, groundwater extraction and load calculation on two factors contribute to the rate of land subsidence and provide scientific basis and technical support for the important area of Ningbo plain land subsidence control plan.On the basis of Ningbo plain basic geological, engineering and environmental geology and groundwater extraction and analysis of land subsidence monitoring data on the constitutive model analyzed the main characteristics of land subsidence in the region and the main soil, causes and effects of factors on land subsidence conducted a systematic analysis of land subsidence study presents mathematical models and numerical methods to consider the role of load and groundwater, graphics platform based uGIS corresponding computer software, the establishment of a numerical model of Ningbo plain land subsidence, settlement area of the main factors affecting land subsidence simulation analysis, and land subsidence was simulated to predict trends, mainly obtained the following conclusions, understanding or outcomes:1. Numerical methods of land subsidence considering both effects of load and groundwater exploitation and new softwareAccording to Ningbo plain land subsidence factors and mechanism to Biot model, a mathematical model of land subsidence is established considering both effects of the load and groundwater exploitation. The model uses seepage flow-pipe flow model to simulate and calculate the pumping well mixed. Using of empirical formula stress and discrete numerical methods, the hydrogeological parameters and geotechnical parameters were estimated, and then were determined by calibration methods.FORTRAN language is used to program the land subsidence numerical procedure. Based on GIS platform, the module of the graphical data input and displaying result were written as uGIS. Land subsidence information for the data management and integration of numerical simulation of land subsidence can be carried out in this software.2. Ningbo plains stratification and stress-strain characteristicsBased on the basic geology, hydrogeology, engineering geology drilling data of the interesting area by and previous studies, Ningbo Plain is on the accumulation of Cretaceous synclinal basin formed due to repeated transgression terrestrial and marine role of Alluvial the region formed the average thickness is about100m staggered Quaternary sea and land, and its thickness increases from southwest to northeast.According to the hydrogeological properties of layers around the study area includes two major Quaternary aquifers:a thickness of about10-15meters, its roof about50meters in depth and80meters respectively. According to the geotechnical properties of layers around the region can be divided into six small Quaternary layers of soft soil were the first group, the first hard soil layer, the second layer of soft and hard, I, aquifers, fourth hard section II soil and aquifer.Based on monitoring data of land subsidence, groundwater extraction and precipitation recharge and geotechnical test data, we summarize the main characteristics of soil deformation and constitutive model. The deformation mainly includes three forms:elastic, plastic, and elastic-plastic. Aquifer Ⅱ and the hard soil I can be taken as elastic deformation; aquifer I, fourth hard layer, and second soft and hard layer mainly be taken as plastic deformation; soft soil I based on the plastic deformation. 3. Numerical simulation of land subsidence in Ningbo plainIn this paper, a numerical model of land subsidence is established using the new software developed in this study, considering both groundwater extraction and load effects in the study area. Numerical simulation results showed that the variable parameter groundwater exploitation-land subsidence coupling model can reflect real land subsidence caused by both groundwater exploitation and load. Although it is more reasonable to consider changes in the parameters in theory, but if there is a significant effect pending comparative analysis and practical application to verify. We verify that the dynamic changes of the groundwater in the area are mainly affected by groundwater exploitation-recharge control. The deformation of first group soft soils is the caused by groundwater extraction, while the deformation of first group soft clay soils is not only caused by groundwater exploitation.Our numerical simulation results show that the first group was due to consolidation of soft clay soil, easily deformed under load and settling its own weight, load the first major impact of soft soil shallow land subsidence group. The first set of soft soil, the bottom by the double impact of groundwater extraction and loading. The main impact of groundwater exploitation in deep layers of land subsidence bits (including the first hard soil layer, the second layer of soft and hard, Ⅰ of the aquifer, the fourth hard soil and Ⅱ aquifer).The land subsidence is calculated by the numerical models considering both groundwater extraction and load, and the influence region is evaluated. Furthermore, we predict the land subsidence caused by groundwater exploitation and load using the numerical model.4. RecommendationsIn order to more effectively control land subsidence in the area, according to the distribution of land subsidence and its influencing factors and mechanism, we proposed some recommendations as follows:(1) Further optimization of control groundwater exploitation. Although groundwater exploitation is one of the factors for land subsidence, from the perspective of resource utilization, the rational exploitation of groundwater water needs to meet certain requirements, such as emergency water or some special water, or very meaningful. According to analysis, monitoring of land subsidence, groundwater level should be controlled at-20m or more. Avoid concentration of mining, gifted with excellent water, try not to exploit mixed.(2) Optimization of groundwater recharge model. Methods recharge both control land subsidence, but also the sustainable use of resources recycling methods. By recharge, water level should ensure a hydrological year can be restored to the normal water level, water quality, water quality should not be worse than the original.(3) Improve the groundwater and land subsidence monitoring network. Monitoring is necessary to consider the focus areas, and should take into account the region’s coverage; automated monitoring and manual monitoring combined with appropriate consideration tiered monitoring focus areas.(4) Strengthen the engineering construction management to prevent land subsidence due to construction caused the disaster.Due to the limited time, there are still many problems in this study, which are:(1) since it is difficult to get the information including load distribution, load time, load size and other information, with great uncertainty, it may have a greater impact on the results. We recommend strengthening information gathering and surveys to improve model accuracy.(2) In this paper, we developed a simulation software package for simulating the land subsidence. For the method, it is more powerful to describe the mechanism of land subsidence. However, due to the uncertainties of the model parameters and grid system impact on the calculation results of the model, we suggested to strengthen research in this area in the theory and practical application.