Study On Stress-deformation Characteristics And Engineering Effects Of The Suture Zone In Sichuan-Tibet Railway

The Sichuan-Tibet railway project straddles the crust-block collision zone such as the Bangong Lake-Nujiang suture zone,the Lancangjiang suture zone,and the Jinsha River suture zone.The combination of complex geological construction features and mechanical effects of rock masses has great restrictions on the construction of the Sichuan-Tibet Railway.Based on the analysis and analysis of existing geological,geophysical,neotectonic and seismic research data,the dissertation systematically and in-depth geological survey and test work on the ground,in order to profoundly understand and master the three suture zones.On the premise of the geological construction-tectonic characteristics of the plate-bonded zone,a conceptual model of the “geology-rock mass mechanics” capable of objectively reflecting the overall structural characteristics of the crust rock mass in the bonded zone was established,through rock construction,regional stress data,and combined GPS displacement characteristics.The analysis of the model parameters and boundary conditions was performed.ANSYS finite element rock mechanics calculation method was used to analyze the stress-deformation distribution characteristics of the crust rock mass in the plate-bonded zone,and to deepen the understanding and understanding of the dynamic mechanism of the crust structural dynamics of the suture zone.Based on this and combined with geological survey data,the engineering effect issues such as strain energy density,geological disaster control effect,and major engineering geological problems in the plate-bonded zone are discussed.The suture zone,magmatic rock zone,and low-velocity layer of the crust are high-gradient zones of stress and strain.The displacement of the crust and rock mass decreases from a certain gradient from west to east,and falls abruptly at the fault.The low-velocity layer deforms more strongly than the sedimentary caprock and the crystalline basement;the compressive deformation of the jointed rock mass is significant.The dislocation between fractures and the compressive deformation of the bond band itself have a "reduction and shielding" effect on the transmission of tectonic stress.The layered structure of the crustal material leads to the displacement deformation of the weak “low-velocity layer” under the unified tectonic stress field is relatively higher than that of the hard block “floating” on the upper part,and the movement is similar to the low-velocity layer “driving” the upper crust.Rock masses undergo near-horizontal migration.The displacement above the low velocity layer on the west side of the Jinsha River junction is extremely large,and the sudden drop in displacement occurs when the low velocity layer is crossed.The magmatic rock band on the west side of the Lancangjiang River-bounding zone was cut to the crystalline basement,and did not reach the lower “low-velocity layer”,and the lower low-velocity layer deformed more strongly than the upper-lower velocity layer.The Jinsha River suture zone,Gongjueyong-Hengyong fault zone,the northeastern side of the suture zone and the east side of the Bangonghu-Nujiang suture zone are areas of high strain energy density with strong activity,and the railway project should be connected with the tectonic line.The direction is a large angle crossing.The Jiangda tectonic magmatic rock belt,the magmatic rock belt on the west side of the Lancangjiang merging zone,the Shubola magmatic arc zone,and the Bangong Lake-Nujiang suture zone have low strain energy density areas with high stress levels and relatively small strain values.The problem of high ground stress in tunnel engineering in the region should be considered.In the high gradient region of strain energy,there is a problem that the deformation of the rock mass is inconsistent and the local deformation is too large.The deformation resistance of the engineering facilities in the region should be appropriately improved.Geological disasters were developed in the Jinshajiang-Bayu Ouqu section and the Zangqu-Zhiqu-Duqu watershed in Jiangda county.The Luqu-Nujiang valley(ancient landslide)and a huge alluvial fan in the Beisu county developed.The control effect of the suture zone on the development of geological hazards is mainly reflected in three aspects: rock construction,structural deformation,and superficial geological action brought about by the dramatic uplift of the crust.The main engineering geological problems of the suture zone are:(1)high geostress: the west side of the Jinshajiang suture zone(Jiangda tectonic magmatic rock zone),the southwest side of the Bangonghu-Nujiang suture zone and the southwest side of the Bangonghu-Nujiang suture zone(Gandise-High ground stress in tunnels of the Shubola Ridge magmatic arc zone of the Nyainqentanglha Land Block;(2)Strong structural deformation in the Jinsha River suture zone and the Bangong Lake Nujiang suture zone,with development of geological disasters such as landslides,debris flows,and collapses;(3)The clastic rocks and clay rocks of the northeastern part of the Jinshajiang suture zone(Dage-Zhongdian block)and the Bangonghu-Nujiang suture zone are constructed and developed.Large deformation of the tunnel.Affected by the stress-strain shielding effect of the magmatic rock belt,the Beiqiantang-Changdu-Simao block is relatively stable.Combined with its stable Mesozoic strata,the engineering geological conditions are relatively good.