Abstract
During the blasting excavation of the large-span tunnels, the instability of the blasting caused the overexcavation phenomenon, making the grille arch difficult to land completely in the primary support of the tunnel, thus forming an arch foot defect. In order to reduce the security issues of tunnel engineering construction and scientifically evaluate the influence of arch foot defects on the force performance of the overall structure of the arch frame, combining the Qingdao Metro long-span hard rock tunnel project, this paper designs two grille arch test sections with arch foot defects and one conventional section to carry out field tests. Combining with FLAC3D numerical simulation, the results of the study were used for analyzing the stress characteristics of arch foot defect grille arch in the primary support of the tunnel. The results indicated that (1) the arch foot of conventional section arch frame is subjected to the force transferred from the upper part and the deformation pressure of surrounding rock within the arch foot range, and the upper transfer force borne by the arch foot mainly comes from the deformation of arch waist. (2) When the arch frame has arch foot defects, the deformation of surrounding rock at the arch foot and the deformation transferred from the upper part mainly depend on the shotcrete, thus resulting in the increase of shotcrete strain. (3) Anchoring bolt and shotcrete can integrate the grid arch with the surrounding rock, thus bearing local loads in the arch crown, arch waist, and shotcrete. (4) The numerical calculation of arch frame with arch crown, arch waist, and arch foot defects claims that the force reduction of the arch frame caused by the arch foot defect was the most obvious, and the calculation results were consistent with the actual project.
Highlights
It is the rapid development of transportation that has accelerated the construction of many tunnel projects all over China, such as Chengdu Longquanshan Tunnel, Ji’nan Yellow River Tunnel, and Qingdao Metro Tunnel
The results show that after the installment of tunnel lining, the lining pressure and steel rib stress increase rapidly and tend to be stable until the surrounding rock is disturbed by the subsequent excavation; Li et al [3] obtained the surrounding rock pressure and the mechanical characteristics of each subcomponent of the primary support system through on-site monitoring and pointed out that the surrounding rock pressure, steel frame stress, and shotcrete stress changed sharply with the excavation process, and the sensitivity decreased in turn; and Luo et al [4] took Loess Tunnel as an example and combined the primary support monitoring results with FLAC3D numerical simulation, and the primary support stress
It can be seen from the figure that before the excavation of the arch foot, both sides of the arch steel rib of the arch crown and arch waist of the monitoring section were compressed, and the change law can be basically divided into three stages: rapid growth stage, stress decline stage, and stable stage
Summary
It is the rapid development of transportation that has accelerated the construction of many tunnel projects all over China, such as Chengdu Longquanshan Tunnel, Ji’nan Yellow River Tunnel, and Qingdao Metro Tunnel. The results show that the stress on the inner side is generally greater than that on the outer side at the same measuring point; Song et al [15] designed a kind of spatial steel tubular grid (SSTG) with high strength and large stiffness, the bending test of the arch frame was carried out through the combination of test and numerical calculation, and the mechanical performance of the arch frame in the whole loading process was studied; Hou et al [16] tested the mechanical properties of thin-walled concrete-filled steel tube arch and compared it with traditional grid steel frame, and it is concluded that the deformation resistance of thin-walled concrete-filled steel tube arch frame is stronger; Wen et al and Li et al [17, 18] established the foundation curved beam mechanical model of tunnel primary support and deduced the internal force of tunnel steel arch through tunnel monitoring data; and Li et al [19] embedded the yield criterion of beam element into FLAC3D main program by using Fish language and realized the correction of beam model and the yield failure simulation of supporting arch. The study has guiding significance for the support design and construction of large-span hard rock tunnel
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