The deformation of Muzhailing deep tunnel is about 2.3 m in the process of construction, which is difficult to be controlled by the traditional “anchor-grouting integration” support system. This paper deeply analyzes the geological characteristics, rock mechanics characteristics, and surrounding rock failure characteristics of Muzhailing tunnel. The deformation mechanism and the failure of the support system are analyzed through the numerical simulation, theoretical analysis, and field test. The authors propose support measures suitable for Muzhailing tunnel based on the analysis results. The maximum buried depth is 600 m, and the engineering rock mass at the depth has nonlinear physical and mechanical phenomenon. The maximum principal stress of Muzhailing tunnel is 25.7 MPa, which belongs to high-stress joint swelling soft rock tunnel. The NPR cable can achieve large deformation under the condition of constant support resistance. The authors put forward the coupling support mode of “NPR cable + steel arch frame + concrete,” which is based on the idea of transforming the composite deformation mechanism to a single type. The stress concentration appears in the range of 12 m in the surrounding rock circle, and the lateral and vertical stress distributions are relatively symmetrical after the improved support. The circumferential strain of the surrounding rock is greatly reduced, and the range of strain is reduced by 10%. The field monitoring results show that the new support system can well control the large soft rock deformation of Muzhailing tunnel (0.5 m). The support strategy proposed can effectively control the large deformation and promote the formation of new support concept for deep tunnel.

Throughout engineering construction, large deformation disasters in soft rock tunnels are encountered increasingly frequently. Therefore, structural health monitoring not only ensures accurate construction management but also provides a basis for dynamic adjustment of the support structure. The existing monitoring technology has certain shortcomings, such as poor anti-interference ability, non-real-time operation, and great security risks. Consequently, high-precision real-time monitoring has become a key scientific issue in tunnel engineering. For this work, multisource information fusion technology was adopted, while data security reserve systems, such as cloud server (ECS) based on the fiber Bragg grating multisource sensing system, cloud database (RDS), and cloud website, were embedded into the No. 2 inclined shaft of the Muzhailing tunnel. Based on the negative Poisson’s ratio (NPR) anchor cable control technology for large deformation of the soft rock in the No. 2 inclined shaft of the Muzhailing tunnel, reasonable and effective intelligent monitoring was carried out for tunnel construction. Monitoring and early warning cloud service platforms, based on the Internet of Things and cloud technology, could quickly produce query and statistic tunnel monitoring information. The monitoring system provided the collection, transmission, storage, processing, and early warning information sending of data, such as NPR anchor cable axial force, steel arch stress, deep surrounding rock displacement, surrounding rock deformation, and contact pressure between primary support with secondary lining. This monitoring system ensured construction safety and provided monitoring application case support for the related problems of similar projects.

Many problems are encountered in the construction of bifurcated tunnels due the abrupt change in section, small clear distance, and large section. Progress in the direction of tunnel construction is limited by the large-span section; therefore, a special method of construction that involves constructing a guiding tunnel first followed by reverse excavation was adopted to construct the large-span bifurcation section of the Liantang tunnel of Shenzhen Eastern Transit Expressway in China. The stability criterion of the surrounding rock of the middle wall in the section of multiple arch and small clear distance is studied by theoretical analysis, and the internal stress and corresponding ultimate strength of the middle wall under different buried depths and widths of the middle wall are calculated by the stability criterion. In this study, 3D finite-difference software was used to simulate the excavation process under forward and reverse excavation conditions. The results show that the displacement field and internal force field distribution are similar for both excavation methods, and the tunneling first and reverse excavation construction method is safe and reliable.

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