Research And Optimization Of Dynamic Partition Method For Large Section Gradual Change Tunnel Of Urban Subway

In recent years,with the rapid development of urban subway in China,the number and mileage of construction have increased year by year,and great achievements have been made.Because of its large span and complex construction process,shallow-buried and underground excavation of largesection tunnel in urban metro has caused many disturbances to surrounding rock,which makes surface settlement difficult to control and makes construction difficult.Traditional methods have certain limitations.Most engineers put forward new methods according to the limitations of traditional methods and construction environment.Based on the background of the tunnels excavated in Tiantongyuan South Station of Beijing Metro Line 17,this paper puts forward the dynamic zoning method,and studies the construction parameters,space-time benefit and support dismantling scheme of the dynamic zoning method with the help of MIDAS-GTS and FLAC3 D.The construction scheme is optimized by FAHP-grey relational degree-TOPSIS theory to ensure the construction process of the tunnel.Stability in.The research contents and achievements of this paper are as follows:(1)In order to verify the construction stability of the new method,the FAHP-Grey Relational Degree-TOPSIS method is proposed for multiobjective decision-making.Compared with the traditional Grey Relational Degree Method and Entropy Value Method-Grey Relational Degree Method,the accuracy of this method can be determined,and it can still be accurately selected when there are fewer samples and the gap between samples is small.The best scheme can also highlight the advantages of this scheme.(2)By changing the number and relative position of temporary support,the influence of the size of temporary guide tunnel on tunnel stability is analyzed.The results show that the more the number of temporary support,the more uniform the distribution position,the stronger the stability of tunnel.However,the larger the number,the higher the corresponding economic cost and time cost.Therefore,when the span of the temporary guide tunnel from left to right is 5 m,5 m and 4.5 m,the stability of the tunnel can be enhanced and the cost can be saved.(3)By means of numerical simulation,the construction scheme of dynamic Partition method is optimized.According to the factors affecting the stability of tunnel,such as the strength and scope of reinforcement zone,construction sequence,construction step and staggered distance between fixed Partition and dynamic Partition,the L16(4~*4)orthogonal test table is established.Based on FAHP-grey relational degree-TOPSIS method.Orthogonal experiments were carried out for analysis.The optimum scheme is as follows: the construction step is 2 m,the strength of reinforcement zone is 200 MPa,the range is 3 m,the staggered distance between fixed and dynamic zones is 10 m,and the construction procedure is serial number 2.(4)In this paper,the limitations of traditional construction methods are summarized and studied,and a dynamic zoning method suitable for shallow-buried and underground excavation of large-section tunnels in Metro is proposed.The feasibility of the dynamic zoning method is verified by comparing the dynamic zoning method with the traditional double-sided-wall pilot method and CRD method through numerical simulation.The results show that the dynamic zoning method is feasible.Except that the horizontal displacement of the arch waist is larger than the other two methods,the other evaluation indexes are smaller than the two methods.The advantages and disadvantages of the three methods are as follows: dynamic zoning method > double-sided guide hole method > CRD method.(5)According to the factors affecting the time-space effect of the tunnel,the L16(4~*4)orthogonal test table is established.Based on FAHP-grey correlation degree-TOPSIS method,the orthogonal test is analyzed.The results show that the exposure time without support has the greatest influence on the stability of the tunnel,the construction speed of the tunnel has the smallest influence on the stability of the tunnel,and the initial support dismantling time.The influence of the construction time of the second lining and the second lining on the stability of the tunnel is in the middle.