Study On Mechanical Behavior And Surrounding Rock Classification Of Variable Cross-section Double-line Parallel Metro Tunnels

Due to the needs of subway construction and geological conditions,subway tunnels have different cross-sectional forms.From the perspective of overall planning of subway construction,to ensure safety during subway construction,higher requirements are placed on the classification of subway tunnel surrounding rocks.Based on the engineering background of Qingxiushan Station of Nanning Rail Transit Line 3,this study related research on 2 parallel tunnels of the station.First of all,the paper analyzed the relationship between tunnel construction mechanics and surrounding rock classification theoretically,and pointed out the correlation between the two,which provided the necessary theoretical basis and logical justification for the full text research.Then,combined with the actual engineering of Qingxiushan Station,the Midas gts / NX numerical analysis software was used to analyze the mechanical behavior of the variable cross-section construction of the left line main tunnel and the surrounding rock stress and displacement caused by the construction of the two main tunnels.Field test data verified the correctness of the model.At the same time,necessary research had been done on the advance support effect of tunnel surrounding rock.Finally,a new method of surrounding rock classification was proposed based on the toughness theory,and the application of the classification method in practical engineering was verified by the Euclidean distance method.Through the above research,the following main conclusions were drawn:(1)Affected by the excavation of the upper foundation pit,at the same type of variable-section tunnel,the settlement of the vault of the left-line main tunnel at a shallower depth is smaller than the value of the vault settlement at a deeper depth.The lining structure deformation caused by the excavation of the left-line main tunnel using the two methods of the CD method and the three-step method is within the control value required by the code.Therefore,the original design of the CD method is changed to the three-step method.(2)There are two left and right tunnels at the same buried depth and the same type of cross section.The displacement and deformation of the surrounding rock caused by the excavation of the left tunnel is greater than that of the right tunnel.Through the study of the change of the surrounding rock stress after the completion of the left-line tunnel excavation and the double-line tunnel excavation,it can be found that the construction of the later-built tunnel will have a certain effect on the surrounding rock stress of the first-built tunnel.Advance tunnel reinforcement measures have played a key role in controlling ground deformation.(3)The concept of resilience of the surrounding rock of the tunnel was refined,and the two important characteristics of the time and functional properties of resilience were pointed out.Based on this,five grades of the resilience of the surrounding rock of the subway tunnel were divided.Taking the left tunnel of Qingxiushan Station subway tunnel as an example,the correctness of the surrounding rock resilience classification method is verified.