Mechanical responses of closely spaced large span triple tunnels

Multi-LOD BIM for underground metro station: Interoperability and design-to-design enhancement

Mechanical responses of surrounding rock mass and tunnel linings in large-span triple-arch tunnel

Mechanical responses in the construction process of super-large cross-section tunnel: A case study of Gongbei tunnel

The excavation of large-span triple tunnels using drilling and blasting method inevitably causes complicated load transfer effects and induces potentially damaging ground vibrations. In this study, the structural responses (including the surrounding rock pressure, normal-contact pressure between the primary and secondary linings, internal forces in the secondary lining) and the seismic responses (including peak particle velocity and corner frequency), are systematically recorded. It is found that the first-excavated left tunnel is influenced heavily by the excavation of the last-excavated middle tunnel, whereas it is hardly affected by the excavation of the second-excavated right tunnel. The load carried by the primary lining is approximately three times as that carried by the secondary lining. The middle tunnel was in the least desirable state due to the formation of the large Protodyakonov’s equilibrium arch (PEA). Based on timely feedback of the comprehensive monitoring system, a series of vibration-reducing techniques were applied and effectively guaranteed safety during blasting construction. By referring to Chinese codes, the minimum safety factor of the secondary lining is 1.3; the maximum PPV (0.15 cm/s) is lower than the allowable value; and the corner frequency (40-140 Hz) will not cause resonant vibration of the Great Wall.

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Geotechnical monitoring and safety assessment of large-span triple tunnels using drilling and blasting method

The platform of the Badaling Great Wall Underground Station consisted of large span triple tunnels. The triple tunnels passed through several major faults. Based on preliminary in situ monitoring, the interaction behavior among triple tunnels was significantly severe, and the original supports failed to meet the safety requirement. Therefore, pipe roof pre-support (PRPS) and curtain grouting pre-reinforcement (CGPR) were used as the pre-construction techniques. By numerical investigation, the pipe diameter, the arrangement angle of PRPS, and the grouting thickness of CGPR were optimized as 108 mm, 150°, and 3 m, respectively. According to numerical results, PRPS predominantly bore loose rock and reduced mean crown settlement (MCS), while CGPR primarily improved the mechanical properties of rock and decreased the pillar plastic ratio (PPR). PRPS and CGPR had complementary advantages in time, space, and mechanical properties. PRPS could timely form a strong arch structure far ahead of the tunnel face, CGPR could effectively restrict the development of plastic zone. They mutually and actively formed a strong permanent ring in front of the tunnel face. After the field application of PRPS and CGPR, the mean surrounding rock pressure reduced by 33.4%, the MCS reduced by 58.7%, and no support damage was observed. The excavation safety was guaranteed.

https://www.mdpi.com/2076-3417/10/9/3186/pdf

Combined Application of Pipe Roof Pre-SUPPORT and Curtain Grouting Pre-Reinforcement in Closely Spaced Large Span Triple Tunnels

Numerical modelling and field monitoring study on large-span tunnelling using pretensioned bolt–cable combined support system

To confirm the robustness of a tunnel, the quality of the rock mass is usually evaluated by several rock mass classification (RMC) systems before its design. Besides, the accuracy of the RMC should be checked through the correlations between different RMC systems. The relationship between the different RMC systems and P-wave velocity indexes is conducive to the interpretation of the rock mass. Here, based on linear or nonlinear regression analysis of 231 samples, we established the RMR–Q, [BQ]–Q, and [BQ]–RMR relationships with R2 = 0.935, 0.732, and 0.759, respectively. Further analysis showed that the grading differences between any two RMC systems yield different characteristics when the rock mass score is at different intervals. To evaluate the relations between RMC indexes and P-wave velocity, we conducted a group study on the different grading differences among RMR, Q, or BQ. Depending on the consistency of the grading results, we arranged the values from large to small as the amplitude of the slope of the curve, and the grading results differed by either one or two levels. Our data demonstrated that the grading differences between the systems are proportional to the discontinuous state of rock mass in the classification. In addition, the classification results of Q, RMR, and BQ showed more significant differences when less consideration is given to the integrity of the rock mass.

Ran Li

Papers

Mechanical responses of closely spaced large span triple tunnels

Geotechnical monitoring and safety assessment of large-span triple tunnels using drilling and blasting method

Combined Application of Pipe Roof Pre-SUPPORT and Curtain Grouting Pre-Reinforcement in Closely Spaced Large Span Triple Tunnels

Numerical modelling and field monitoring study on large-span tunnelling using pretensioned bolt–cable combined support system

Dissecting the Robustness of the Rock Mass Classification Methods Used in Jiaozhou Bay Subsea Tunnel