| The tunnel in cold region has gradually become a special project in infrastructure construction,due to the poor geographical environment and the difficulties in construction and operation.The geographical environment of the tunnel area is all high-altitude mountains,and the tunnel construction and operation phases are usually affected by groundwater seepage problems.As a result,engineering disasters occurred and the actual service life of tunnel was shortened.Because the cold-proof drainage hole and other drainage facilities are to be built in cold regions,and in order to shorten the construction period during tunnel construction,the parallel guiding adit will be designed to increase the number of tunnels in due course.This is a tunnel project under group hole.Compared with single-tunnel tunnels,the construction of tunnels under group hole will generate multiple disturbances to the surrounding rock,which will have a greater impact on the stress and deformation of adjacent tunnel structures.Studying the seepage-stress coupling during tunnel construction under group hole has a certain effect on the rational design,safe construction and operation of practical projects.This article takes the Dunhuang-Geermu Railway as the background,the construction section was took as the research object,which consisted with the main tunnel,the parallel guiding adit and the cold-proof drainage hole simultaneously.The status and methods of seepage development,the interaction between seepage field and stress field,and the development of seepage-stress coupling calculation are systematically introduced.Based on the theory of research on the seepage-stress coupling by scholars at home and abroad,using the MIDAS/GTS finite element software to establish a three-dimensional numerical model under group hole,by analyzing and studying the mechanical properties of the tunnel structure which under group hole when the stress field acts alone,the seepage field alone and the seepage-stress coupling effect.The following conclusions can be drawn:(1)Different construction modes are determined by the properties of different surrounding rocks and section size of the tunnel,and they also have different influences on mechanical properties and construction schedule of the tunnel structure.This paper studied the mechanical properties by analyzing the displacement,stress,bolt axial force,initial support stress and the plastic zone of tunnel surrounding rock.(2)Regardless of horizontal displacement or vertical displacement,the effect of one-way construction on the displacement of surrounding rock is less than that of two-way construction,and the vertical displacement is increased by 5-8% in the two-way construction.The maximum value of the equivalent plastic strain of the four excavation methods is located at the side wall of the cold-proof drainage hole,and the equivalent plastic strain is less than the full section method when the step method is constructed.(3)The tunnel stress is reasonable during the construction of the step method,and the maximum principal stress of the surrounding rock in the four excavation methods is located at the bottom of the main tunnel.The minimum value is located at the left arch of the main tunnel.The compressive stress at the arch foot of the main tunnel is 8.2% less than that of one-way construction in the whole section method.The compressive stress at the arch foot of the main tunnel is 13.4% less than that of the one-way construction.(4)The maximum tensile strength of the anchor rod in the four excavation methods is less than the ultimate tensile strength of the bolt,and the tensile stress appears in the lining vault at the construction of the step method,and its value tends to the tensile strength of C25 concrete.During the tunnel design and construction,the lining thickness or concrete strength should be increased to ensure the safety construction and operation of the tunnel.(5)The deformation of the main tunnel and cold-proof drainage hole is relatively reasonable and meets the maximum freezing depth requirement when the appropriate buried position of cold-proof drainage hole was 5 m below and 19 m left of the main tunnel.Therefore,on the basis of accelerating the progress of tunnel Construction,for grade III and below rock grades,two-way excavation using the step method can speed up the construction progress and ensure the safety of the tunnel to some extent.(6)Analyzed the seepage field by applying different infiltration coefficient grouting ring under the condition of the best thickness is 2m and permeability coefficient of surrounding rock is 0.00029m/d,0.00085m/d and 0.00334m/d.It can be seen that the high horizontal grouting ring is equivalent to forming a layer of anti-seepage protection layer around the tunnel excavation section,which minimizes the seepage velocity and seepage flow of each hole in the tunnel construction.It is important to apply the grouting ring to the tunnel stability and the bearing characteristics of the support structure,whether for the construction period tunnel or the operation period tunnel.(7)We can learn from the comparison and analysis of the tunnel structure stress characteristics,the seepage field has great influence on the tunnel vertical displacement.In the coupling case,the vertical displacement settlement of the vault is 25.7% larger than the non-coupling case.It also has great influence on the surrounding rock structure,and in addition,the disturbance of the surrounding rock in the excavation process leads to a large force of supporting structure,which is unfavorable for tunnel safety construction and long-term operation.Therefore,the influence of seepage field on stress field is not neglected in tunnel support structure and safety construction design. |
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