(1. State Key Laboratory of Geohazard Prevention and Geoenvironment Protection，Chengdu University of Technology，Chengdu，Sichuan 610059，China；2. College of Environmental and Civil Engineering，Chengdu University of Technology，Chengdu，Sichuan 610059，China；3. Geological Innovation Studio of CREEC，Chengdu，Sichuan 610031，China)
Abstract：The Ya¢an—Xinduqiao section of the proposed Sichuan—Tibet railway is located in the geological structure intersection area of Sichuan，Yunnan and Tibet with extremely complex geostress. Research on the present geostress field in this area is conducive to the scientific construction of the Sichuan—Tibet railway. Based on the measured data of in-situ geostress by hydraulic fracturing method，the characteristics and distribution of in-situ geostress as well as engineering effects in the three sections including Ya¢an—Ludin，Luding—Kangding and Kangding—Xinduqiao sections of Sichuan-Tibet railway are analyzed. The results show that the main stress value has a good linear relationship with the burial depth，and that the maximum horizontal main stress increase gradients of the three sections are respectively 3.2 MPa per 100 m，2.7 MPa per 100 m and 3.6 MPa per 100 m，among which the growth gradient of Ya¢an—Luding section is the largest with a measured maximum horizontal main stress more than 51 MPa at 1300 m the burial depth. The orientation of the maximum horizontal principal stress in this area is NW，which is consistent with the current tectonic direction. Under the control and influence of canyon topography and faults in the area，the maximum horizontal principal stress orientation of some individual measuring points is NE. The lateral pressure coefficients of the three sections are all greater than 1，which indicates that the area is mainly affected by horizontal compression structure. The lateral pressure coefficients of the three sections with a buried depth less than 300 m，350 m and 500 m are 1.7，2.3 and 3 respectively，which shows that the in-situ geostress of the shallow buried section is also controlled by the topography of high mountains and valleys and the superimposed influence of slope stress field. According to the influence of the angle between the maximum horizontal principal stress direction and the tunnel axis on the stability of surrounding rock，the route layout of Ya¢an—Xinduqiao section of Sichuan—Tibet railway is generally reasonable，although there maybe exist some unfavorable circumstances for surrounding rock stability only at the exit end of Paomashan and Kangding tunnels and the deep buried section of Zheduoshan tunnel(buried depth about 1 000 m). The rock burst of II and III surrounding rock of tunnels is mainly slight and medium，while the hard rock with a large buried depth(more than 870m，1 140 m and 930m in Ya¢an—Luding，Luding—Kangding and Kangding—Xinduqiao sections，respectively) may occur strong rockburst. The large deformation of IV and V surrounding rock presents mainly slight，moderate or strong. Strong deformation may occur for IV surrounding rock with a buried depth more than 1 330 m and V surrounding rock with a buried depth more than 940m in Ya¢an—Luding section，V surrounding rock with a buried depth more than 1 410 m in Luding-Kangding section and V surrounding rock with a buried depth over 960m in Kangding—Xinduqiao section.
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2021, Vol. 40 
