Analysis Of Additional Stress Field In The Head Area Of Three Gorges Reservoir

Large reservoirs,as major water civil infrastructures,play an important role in the national economy and people's livelihood.However,with the establishment of large reservoirs,small and medium earthquakes continue to occur around these reservoirs,and sometimes even large earthquakes occur around the reservoirs.This topic——reservoir-induced earthquakes,has attracted the interest of many researchers,and with the establishment of a series of large-scale hydropower stations in the southwest of China in recent years,new challenges have been raised for this topic.At present,there are generally two qualitative and quantitative research methods for research on reservoir-induced earthquakes.In this paper,from the perspective of mechanics,numerical simulation is used to study the induced earthquakes in the Three Gorges reservoir area.Based on the results of the simulation calculations,the changes in the additional stress field and pore pressure field before and after the impoundment were analyzed,and the regional stress fields before and after impoundment were compared to study the possible causes of the induced earthquakes in the Three Gorges Reservoir area.The main content of the paper is as follows:1)The first chapter introduces the research history of reservoir-induced earthquakes,especially the numerical calculation research before and after water storage in the reservoir head area.The shortcomings of previous research are mainly due to the following three points: the first one is that the previous researchers failed to consider the 'Canyon effect' brought by the terrain fluctuations;the second is that it failed to calculate the fluid-solid coupling model;the third is that A large amount of observation data has been accumulated which(gravity field,earthquakes,etc.)can be used to test the model.Only one of them was considered in the previous research,or none of them were considered.This article will make corresponding improvements on the above three issues at the same time;2)The second chapter introduces the geological background and main faults of the Three Gorges Reservoir area(Xiannvshan fault?Jiuwanxi fault and Gaoqiao fault),and paves the way for later modeling.The third chapter introduces the basic theory of fluidsolid coupling theory.Then based on the geological data in Chapter 2,a calculation model of the Three Gorges Reservoir head area is established;3)In chapter 4,calculation is done based on the established three-dimensional model when the water level changes for 72 months from the beginning of storage.And the storage levels are located at 135 m,145m,156 m,172,and 175 m,respectively when the model is run.During this period,the changes of the additional stress field and pore pressure field in the head area of the Three Gorges Reservoir,and can explain the cause of the Hujiaping Ms4.1 earthquake in the head area of the Three Gorges Reservoir.With the gravity observations,this article compares the numerical results with gravity observations.4)Chapter 5 summarizes the research content of this article,points out the shortcomings of the model,and gives the direction of future research.In this paper,the causes of earthquakes are explained from the mechanism of reservoir-induced earthquakes.Based on previous research,numerical simulation methods are used to establish a calculation model of the Three Gorges Reservoir head area that is closer to the actual conditions.The calculation results are used to explain the earthquakes that have occurred during the storage.It also points out the areas where the additional stress field and the pore pressure field are relatively dangerous.These areas are likely to induce earthquakes in the future.The research in this paper is of great significance not only for the study of reservoir-induced earthquakes,but also for the application of disaster prevention and control in the future development of hydropower in Southwest China.