| Transportation is essential to rejuvenate the country,is the foundation of a strong country.With the continuous development of our country ’s transportation,our country is increasingly becoming a transportation power which focuses attention in the world.Making full use of urban underground space is also an important part of sustainable development of urban transportation.In modern cities,the underground transportation network is not only densely distributed,but also exists other engineering facilities for different purposes.Therefore,the construction of new tunnels in cities will inevitably cross or even coincide with the existing operating tunnel routes.At the same time,due to the change of the purpose of use and traffic volume,the number of tunnels with variable section in new urban tunnels is also increasing.Faced with such a complex engineering environment,how to ensure the smooth construction of the new soft rock tunnel with variable section and reduce the disturbance to the existing operating tunnel has become a major difficulty in construction.Based on a new soft rock tunnel underrunning an existing tunnel project,Thesis uses theoretical analysis,numerical simulation,monitoring and measurement methods to study the influence of soft rock tunnel underrunning on the existing operating tunnel and related construction control measures.The main research results are as follows:(1)Theoretical analysis and numerical simulation are used to analyze the mechanical behavior of the initial support structure and surrounding rock at the location of variable section of the new soft rock tunnel under actual working conditions.It is concluded that the expansion of the tunnel with expanded section makes the deformation and stress change of the initial support structure at the location of variable section complicated.The vertical displacement and principal stress of surrounding rock fluctuate greatly under the variable section construction,and the surrounding rock of the right wall of the tunnel with standard section is in a relatively unsafe state.(2)By analyzing the secondary disturbance law of the underpass construction of the new soft rock tunnel with variable section on the existing tunnel,it is concluded that the vertical additional displacement value of the surrounding rock of the tunnel with variable section is as follows from large to small: Arch bottom > left wall > right wall > arch top.In addition to the obvious vertical additional displacement,different degrees of longitudinal additional displacement and rotational additional displacement are generated in the existing tunnel initial support structure.In the variable section position,the maximum additional axial force and maximum additional bending moment of the existing tunnel initial support structure are generated at the arch bottom.(3)Considering the influence of different excavation sequences of new tunnels on the additional displacement,additional internal force and additional stress of surrounding rock of the existing tunnel initial support structure,it is concluded that the optimal construction sequence is to excavate the tunnel with standard section first and then excavate the tunnel with enlarged section.On this basis,the disturbance of new tunnels under different excavation methods and different excavation footage conditions is analyzed.The reasonable construction control technology of new tunnel is obtained.(4)By studying the control technology of the newly built soft rock tunnel with variable section under different supporting conditions,the changes of additional displacement,additional internal force and additional stress of surrounding rock of the existing tunnel initial support structure under different mixing thickness,different steel arch distance and different advanced supporting measures are compared and analyzed.The reasonable support control technology of new soft rock tunnel under the existing tunnel is obtained.(5)The effectiveness of the numerical simulation results is verified by comparing the field measured monitoring data with the numerical simulation results;The nonlinear regression method is used to fit the measured data,and the best fitting function of surrounding rock displacement at the variable section position is obtained,and the best time of the second lining at the variable section position of the new tunnel is obtained. |
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