The Optimize Research On Construction Technology For Mutative Transect Multi-tunnel System Of Urban Metro Crossover Area

In underground engineering of city,the constructions of the tunnel will inevitably produce the land subsidence,the building asymmetry decline and other negative influence to the enviroment,the phenomenon is especially outstanding while constructing mutative and large transect multi-tunnel system of urban metro. Because buildings and various underground pipelines of the circumjacent urban metro are numerous and there usually has strict and restrictive request of the land subsidence for the tunnel construction,it is seems to be very important to make more accurate forecast for the land subsidence and adopt corresponding measures to control the land subsidence.In this paper based on the multi-tunnel between the Hepingxiqiao station～Beituchengdonglu station section of No.5 Beijing metro, and by means of the large and tunnel specialty software Midas/GTS carrying out the finite element numerical simulation,giving emphasis to study the disciplinarian of the ground subsidence while constructing the multi-tunnels,and the scheme optimization of the multi-tunnels construction,and the influence factors of the ground subsidence,and so on.The construction of the double-arch tunnel is a difficult technique for the multi-tunnel system tunnel,the method of construction need design specially.This paper proposed two-hole construction method firstly for the construction of double-arch tunnel and carries on the calculation and comparison to these two kinds of constructions method from the view of construction progress,tunnel safety and so on,and finally confirm that the construction method of the double-arch tunnel is two-hole,and also confirmed the reasonable digging order of section for two-hole method through 2-D numeric simulation research.The pivotal technique for the multi-tunnel system tunnel construction is the transition between different mutative and large transect tunnel.In order to achieve the construction of transition area quickly and securely,this paper proposed a new project of construction fristly adding the horizontal channel in the large transect tunnel and excavates from the large transect tunnel to the small transect tunnel directly,compared with the original project digging the tunnels from the small cross section expanding to the big cross section is superior obviously;This paper carried on the 3-D numeric simulation to the crossover area tunnel based on the optimized construction project,the result is: (1)The surface subsidence is mainly produced in the region above big section tunnel,the max is 37mm when the construction was completed;(2)The result of analysis indicated that,the surronding rock is stable,but the plastic area already to link up at the beginning of construction section,so suggest consolidate 2m scope middle soil pyramid for three hole section tunnel,in the process of construction for small section tunnel;(3) The plastic area and big stratum subsidence were produced by the construction and removing the temporary supports in the big section tunnel,the construction of big cross section tunnel and the construction of double-arch tunnel, the construction of vertically and horizontally the guide hole jaw opening causes, for the construction weak link,should pay attention,must strengthen this spot the supports and protections,the reduction excavates the ruler,seals up the link promptly,in the construction processof the tunnel.(4)The numeric simulation result as the construction process stress,the distortion,the plastic area showes the vertically and horizontally the pilot construction method in the sudden change cross section tunnel and the double hole law construction method in double-arch tunnel are reasonable feasible,construction process is safe,the construction effect is good,can guarantee the environment as well as in the construction process structure own security;The numeric simulation result forecasted the construction effect,provided the instruction to the construction of the tunnel actually,provided the theory basis for the optimized construction project and also the effective reference for the similar project.