Influence Of Construction When The Tunnel Is First Excavation Followed By Working Well On Tunnel Deformation And Control Countermeasures

The shield machines frequently need pass shaft or station foundation during the construction of the various shield tunnels. It always involves the problem of shield machine entering and coming out of hole when shield passes foundation pits. If it adopts the conventional scheme of constructing tunnel after shaft excavation, massive auxiliary measures must be applied, which has big risk and long construction cycle. Especially the problems will be more significent in the project of electricity shield tunnel because of the short distance between working wells. Therefore, the engineering field try the new method that the tunnel is first excavated followed by the working well in the excavation order.According to the previous researches and the characteristic of construction method, the full scale test and numerical simulation as well as theoretical derivation were conducted to deeply explore the common problems and countermeasures when the tunnel is first excavated followed by the working well in the excavation order. And then, some useful conclusions were obtained. Main work and research results in this work are as follows.Through the indoor flexural load test of full scale segment, load-displacement curve was obtained, based on which the curved beam segment stiffness used in theoretical calculation and the equivalent stiffness of shell and solid element segment with different accuracy used in numerical calculation were obtained by back analysis calculation. The 3D refined model of lining and the 3D shell-spring model were established with consideration of the soil-structure interaction. Transverse effective rigidity ratio of segment was calculated, and then the influence of staggered joint and ground resistance on stiffness effective ratio of segment was discussed, which is used for subsequent calculation of longitudinal deformation and segment opening. The results show that the actual stiffness of curved beam, shell and solid element simulating segment in this work is between 8% and 34.9% of the theoretical stiffness. In the typically pearl river delta soft soil layer, the transverse stiffness effective ratio of shield segment commonly used domestic is 0.6, and it is 0.71 when considering the influence of staggered joint which makes the transverse stiffness effective ratio increase by 18.7%. Surrounding rock has a significant effect on deformation of tunnel structures. The ratio of vertical and horizontal displacement of the segment increases with the increase of soil resistance coefficient, which is approximate linear relationship. It indicates that the model test only from the perspective of structure and theoretical derivation which assume the horizontal and vertical deformation of segment are same exist insufficient.3D inelastic analysis was conducted for tunnel construction when the tunnel is first excavated followed by the working well in the excavation order, and scheme comparison of shield entering into working well was conducted based on three aspects which include disturbance to adjacent building, surface subsidence and control internal force of supporting structures. The scheme of shield entering into working well was determined, on this basis, the main problem, which exists longitudinal deformation and segment opening was proposed in view of the regular working well. And then, the distribution of segment opening and its influencing factors were analyzed as well as supporting structure optimization was conducted by orthogonal experiment. The research shows that the scope of influence of foundation excavation on segment opening is mainly resigned to within five segment rings next to the diaphragm wall and analysis of seepage control during the construction can be considered emphatically four joints nearest the working well when the tunnel is first excavated followed by the working well. The effect of soil stiffness, groundwater and seismic action on segment is significant. It suggests that it can do local reinforcement to effectively control segment opening. The more scientific and reasonable supporting scheme was obtained by orthogonal experiment method.Based on the results of segment indoor test and numerical experiments as well as the existing research achievements, a longitudinal equivalent continuous model of shield tunnel was derived in consideration of tunnel transverse characteristic and ground resistance. And then the effective ratio of longitudinal equivalent stiffness was calculated, which is 0.094(about 1/10.6) for the typical geological condition in Guangzhou region. After that, the formula of tunnel longitudinal deformation and segment opening were calculated according to the theory of beam on double elastic foundation, which make up for the deficiency of existing research on longitudinal deformation calculation. Comparing the results of longitudinal deformation and segment opening of engineering instance with numerical results shows that the theoretical calculation proposed in this paper is feasible.The simply-constructed well which is no inner supporting, efficient and circular was proposed. The comparison between simply-constructed well and conventional scheme was conducted as well as parameters sensitivity analysis of the well to open segment deformation was conducted with finite element method. The calculation theory of deformation of open segment was proposed, and the key technology of structures design was explored. The results show that the construction technology, feasibility and influence on surrounding environment of simply-constructed well are superior to conventional one. The project cost of simply-well is only 7% of the conventional scheme, so it greatly saves the cost. It will form unstable structure when local segments are broken and segment deformations greatly increase. The influencing scope of the deformation is manifested on the snap rings and four segment rings on both sides, so it should add temporary supports for spilt ring and four segment rings which are obviously affected to ensure structures safety. The effect of well thickness and soft soil on segment deformation is significant, while the effect of the diameter and spilt rings is very small. The increasing trend of maximum displacement with the increase of the well thickness is quadratic. It suggests that the size of working well should not be big on the premise of meeting the requirements of global stiffness and clearance. The theoretical calculation results of open segment accord with numerical results, which suggests that the theoretical calculation method is feasible and can be used to predict deformation. The key technology of simply-construction well includes temporary supporting system for open segment, the joints design between open segment and simply-construction well, and waterproof design of joints.