Primary Study On Stress Field Characteristics And Genetic Mechanism Of Xianshuihe Tectonic Belt In Western Sichuan

The zone of Xianshuihe tectonic belt in western Sichuan is characterized by frequent earthquake activity and high in-situ stress near the fault zone.It is of great significance to study the characteristics of in-situ stress and its formation mechanism for analyzing and predicting seismic activities in the region and ensuring the safe construction of major projects.In this paper,the in-situ stress data of nine boreholes were collected,and the in-situ stress characteristics of Kangding area were comprehensively analyzed and the possibility of fault sliding instability in the study area was evaluated,and the formation mechanism of the present tectonic stress field in the area was preliminarily explored.FLAC3 D numerical simulation is used to analyze the characteristics of in-situ stress in this area and the causes of the present in-situ stress state are comprehensively analyzed combined with the in-situ stress value.Finally,the stability of the surrounding rock of the tunnel in the study area is predicted and analyzed,and the optimal design scheme of the tunnel is proposed,and the main conclusions are as follows:1.The in-situ stress measurement results in the study area show that the maximum and minimum principal stress and vertical stress in the tested depth range show a trend of linear increase with the depth,and the increase gradient of stress value also changes with the depth.The in-situ stress values in the study area are not uniform in the lateral direction.The lateral pressure coefficient of most measuring points in the study area is greater than 1 and the stress structure is of reverse fault type,which indicates that the current tectonic stress in the study area is dominated by horizontal action.2.The maximum principal stress of the present tectonic stress field in Kangding area has three dominant directions: NE direction,NW direction,and nearly EW direction,and the distribution of stress direction is relatively discrete with depth.The stress state characteristics in the study area are comprehensively affected by the forces between plates,the forces between blocks,the differences in the properties of basement materials within the region,the differences in the activity of fault zones and fault properties,and the geomorphic features of high mountains and canyons.3.The evaluation of fault stability shows that if the stress levels of the Yunongxi fault and Xianshuihe fault continue to accumulate and increase to the critical value of the two faults,the fault sliding instability may occur and lead to the occurrence of earthquake.The continuous accumulation of in-situ stress in the area east of Kangding may be one of the reasons for the occurrence of Lushan earthquake.The continuous accumulation of stress in this area may lead to the occurrence of earthquakes with periodicity.4.The numerical simulation results are consistent with the measured in-situ stress state characteristics in the study area,and the comprehensive effect of steep terrain change and terrain has a great influence on the in-situ stress value in Kangding area.5.Weak ～ medium rockburst may occur in tunnel 1 and 2 in the study area,and medium ～strong rockburst may occur in the sections A,B and C of tunnel 3.The orientation of the tunnel axis,the shape of the tunnel section,and the excavation and support methods of the tunnel should be further optimized.