Study On Large Deformation Classification Of Surrounding Rock In Boshulaling Tunnel Of Sichuan-Tibet Railway

Along the Sichuan-Tibet Railway,the geological conditions are complex,and the tectonic movement is active.The tunnel accounts for more than 85%,among which the length of many tunnels is more than 20km,and the maximum buried depth is more than 1000m.Most of these tunnels are in an environment of high in-situ stress,so they may produce large deformation of tunnel surrounding rock,which will affect the normal construction and operation of railway engineering.Based on the Boshulaling tunnel of Sichuan-Tibet railway as the engineering background,this paper obtained the overall in-situ stress distribution of the Boshulaling tunnel area and the relationship of the three-way principal stress under different lithologies and burial depths by referring to relevant literature and analyzing the measured in-situ stress data of boreholes.Based on the measured in-situ stress data,a three-dimensional geological model of the Boshulaling tunnel area was established,and the overall in-situ stress situation of the tunnel site was further defined.The three-way principal stress at the elevation of the tunnel was obtained,and the in-situ stress grade was classified.Integrity coefficient method and GSI method are used to evaluate the strength of surrounding rock of Boshulaling tunnel body,and the strength stress ratio method is the core,adopts"the railway tunnel design code TB10003-2016","Sichuan-Tibet railway the interim provisions on the high ground stress soft rock tunnel design and in"technical specification for railway compressional surrounding rock tunnel of great deformation rating method,Large deformation classification of surrounding rock in Boshulaling tunnel is carried out,and the results of large deformation classification are obtained.The results show that the principal stress is affected by the buried depth and lithology.In hard rocks such as granite and diorite,when the buried depth is less than 400m,the principal horizontal stress is dominant,and when the buried depth is more than 400m,the vertical stress is dominant.In slates,sandstone,and other rock masses,the horizontal principal stress is dominant at the existing depth,and the vertical stress is the minimum value of the three principal stresses,which shows the lawS_H＞S_h＞S_v.The dominant direction of the maximum principal stress in the whole region is NNE～NEE.The maximum principal stress at the tunnel body position is 4.52～55.35MPa,the intermediate principal stress is 3.28～34.30MPa,and the minimum principal stress is 0.4～24.32MPa.The classification results show that 74.25%of the sections are in the high to the extremely high-stress level,and the extremely high in-situ stress section accounts for 19.99%.The strength of the surrounding rock ofⅣgrade andⅤgrade in the granite and diorite sections of the tunnel is 55MPa and33MPa,respectively,and the strength of the surrounding rock of the slate and sandstone sections is 25MPa and 16MPa,respectively.According to the analysis,the total length of large deformation in Boshulaling Tunnel of Sichuan-Tibet Railway is 1060m,accounting for 3.66%of the total length of the tunnel,of which the class I large deformation length is 190m,accounting for 0.66%of the total length of the tunnel,the class II large deformation length is660m,accounting for 2.28%,the class III large deformation length is 210m,accounting for0.73%of the total length of the tunnel.The classification results of large deformation can provide some reference for the prevention and control of large deformation of surrounding rock of Boshulaling tunnel.