| When a long parallel tunnel is built in the soft surrounding rock with high ground stress,because the strength stress ratio of the surrounding rock is small,the time-space effect of deformation is significant and the multiple tunnels are mutually dry,the deformation of the initial support of the tunnel is characterized by large amount of deformation,fast deformation rate,lag of deformation time and obvious "tunnel group effect",which is often accompanied by cracking of the support structure,peeling off of concrete and twisting and breaking of the steel arch ? When the cross passage construction is carried out between parallel tunnels,the stress and deformation of the surrounding rock and supporting structure in the cross section of parallel tunnels will be further intensified,which will have a great impact on the design and construction.Based on the large deformation section of No.3 inclined shaft working area of yuelongmen tunnel of Chengdu Lanzhou railway,combined with the measured data of the construction site,the mechanical mechanism and main control factors of the large deformation of the parallel multi hole interference in the deep soft surrounding rock are studied by using the method of finite element numerical simulation.Furthermore,the numerical simulation of different layout of cross passage is carried out to study the change rule of stress,strain and plastic zone of cross section surrounding rock and initial support.The main research work and achievements are as follows:(1)Under the condition of high ground stress soft rock,the construction of the back tunnel has a significant impact on the first tunnel.When the vertical stress is the maximum principal stress,the plastic zone of surrounding rock,the deformation of initial support and the maximum stress of initial support all appear in the vault and tunnel bottom.Influenced by the construction of the back row tunnel,the vault and the tunnel bottom have the most obvious changes.The side wall near the back row tunnel is affected more than the side wall far away from the back row tunnel.According to the results of vertical simulation calculation and combined with the field measured data,the main factors that affect the large deformation are given,including:the strength of surrounding rock,in-situ stress environment,the degree of large deformation,the degree of influence of geological structure,the characteristics ofgroundwater development and the group tunnel effect.(2)Under the condition of large deformation,the construction of vertical cross of cross passage has a significant impact on the cross section.After the vertical cross construction of the cross passage,the displacement of the cross section increases obviously,and it changes from the symmetrical deformation to the unsymmetrical deformation on the side of the cross passage,and the local displacement of the intersection ring increases significantly.Under the influence of vertical cross construction of cross passage,the surrounding rock near the cross section is disturbed more than that far away from the cross section(unaffected area),and the surrounding rock near the cross section is disturbed more than that far away from the cross section.The stress concentration degree of the cross section of the middle guide tunnel side is greater than that of the left line tunnel side.(3)The skew construction with the crossing angle of 60 ° has a greater impact on the crossing section.In the construction of cross tunnel,the smaller the cross angle is,the greater the disturbance is.The oblique angle construction of the cross passage also makes the displacement of the cross section increase from symmetric deformation to asymmetric deformation,and the local deformation of the intersection ring is significant.The interference of the surrounding rock on the acute side of the cross tunnel is greater than that on the obtuse side,and the stress concentration effect on the acute side is greater than that on the obtuse side. |
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