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During the construction of a diversion tunnel, geological problems often include faults, fragile strata, hard rock formations, karst landforms, etc., which may have adverse effects on the excavation and construction of the diversion tunnel. Based on the analysis of the engineering overview, this study designed a new construction technology for the excavation of water diversion tunnels in hard rock layers and high-karst areas. Based on tunnel seismic prediction (TSP) technology to achieve advanced geological prediction, combined with actual geological conditions, construction difficulties are analyzed. Then, detection technology is used to collect two-way travel time, amplitude, and waveform data. By processing and analyzing the detection image, the spatial orientation and length of the main tunnel during the construction of the diversion tunnel are calculated. After completing the construction ventilation and wind, water, and electricity layout, the excavation construction procedure is designed. In the specific excavation design, the tunnel curtain excavation technology, tunnel body excavation and support technology, excavation grouting technology, important unfavorable geological tunnel section excavation technology, upper/lower flat section excavation technology, upper/lower curved section excavation technology, and vertical shaft section excavation technology were elaborated. Finally, a plan was made for the reuse process of slag material and a construction quality control system was established. During the testing process, it was found that the antidamage coefficient of the side wall was above 0.9 after using the technology described in this article. Therefore, it indicates that the excavation construction technology designed in this article can ensure the support capacity of the side wall of the diversion tunnel, which is suitable for the excavation of the main tunnel during the construction of the diversion tunnel. [ABSTRACT FROM AUTHOR]

To determine the mechanical properties of the rock mass in the Nansha Branch, three in-situ tests (on-site pressure plate, borehole TV and acoustic wave, and borehole deformation methods) were carried out. Based on the deformation characteristics of the rock mass, the finite element numerical method is used to study the combined stress of the composite lining in the diversion tunnel. The results demonstrate that the deformation modulus values are similar by comparing them to tests of the pressure plate and borehole deformation method. It shows the accuracy and reliability of the deformation modulus obtained by the borehole deformation method. In addition, the deformation modulus of the borehole deformation method and wave velocity were fitted to obtain a power function relationship. The deformation modulus of the pelitic siltstones was estimated. After the Nansha Branch tunnel is filled with water, the maximum principal stress of the pipe piece is 1.953 Mpa in tensile stress, located at the outside of the waist on both sides of the pipe piece. The maximum principal stress of the reinforced concrete lining is 5.407 Mpa, located at the top and bottom inside. The maximum principal stresses have exceeded the standard tensile strength of both the pipe piece and reinforced concrete and are vulnerable to cracking. Special attention should be paid to the deformation of the above parts with regard to long-term operation. [ABSTRACT FROM AUTHOR]

To study the surrounding rock stability of the excavated geologically weak section of the #2 diversion tunnel in the Xulong Hydropower Station, a quasi-3D numerical model was built using the Realistic Failure Process Analysis (RFPA3D) system to simulate the damage and failure process consisting of crack initiation, growth, and penetration in the rock mass after tunnel excavation, and reveal the instability failure mechanism inside the rock mass. Moreover, the microseismic monitoring technology was employed to delineate potential danger areas in the surrounding rock of the tunnel and explore possible instability failure modes. Results indicate that the surrounding rock of the tunnel profile failed as different degrees during the excavation process, most obviously near the vault and corners of the side wall, where tensile failure predominated. As the excavation proceeded, microseismic events increased gradually at the vault and corners of the side wall, and the energy from acoustic emissions accumulated steadily, thus raising the possibility of collapse and rock bursts in this area. The research results can provide technical support for the construction of the diversion tunnel project in the Xulong Hydropower Station and serve as a guide for the construction of similar geologically weak underground projects. [ABSTRACT FROM AUTHOR]