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The MPW that emits from a tunnel's exit when a high-speed train passes through is a serious environmental problem which increases rapidly with the speed of the train. To alleviate the MPW problem at 400 km/h, the aerodynamic effects caused by the hood located at the entrance or exit of a tunnel are studied by numerical method, and the influences of hood geometry, such as an enlarged cross-section, oblique entrance, and opening holes on the MPW, are also investigated. The research indicates that the enlarged cross-section of the hood at the entrance and exit of the tunnel has opposite effects on the MPW, and the oblique section can alleviate the MPW by extending the rising time of the compression wave and increasing the spatial angle at the hood exit. The pressure gradient can be mitigated through delaying the rising of the compression wave by opening holes on the side wall of the hood, and the relief effects of the holes can reduce the MPW further. The MPW problem when a train passes through a tunnel at 400 km/h can be effectively alleviated by an optimized oblique enlarged hood with opening holes, even up to train speeds of 500 km/h. [ABSTRACT FROM AUTHOR]

The control mechanism of prestressed support system is studied by means of three-dimensional discrete element numerical simulation, theoretical analysis, and field measurement. The actual project is selected to analyze, and the control effect is demonstrated. The theoretical analysis results show that the prestressed support can improve the self-bearing capacity of surrounding rock, which is conducive to the stability of the surrounding rock. The numerical calculation shows that, under the control of the long and short cables, the prestress can spread effectively and form two bearing arches. The deformation is difficult to control, which is in the arch crown and the arch shoulder of the tunnel intersection. However, the deformation of the surrounding rock decreases with the increase of prestress. Through the analysis of the measured results, it shows that the pretension support design scheme can effectively control the large deformation of the surrounding rock.

Featured Application: Outcomes of the present research will directly assist the practical design of the high-speed railway tunnel regarding the maximum affordable pressure load of tunnel lining and internal facilities. After decades of research in the field of high-speed railway technique, technology of running high-speed trains at the velocity level of 350 km/h gradually become mature. It is of great importance to capture the variation regular of aerodynamic parameters in the situation that the high-speed train runs at a higher speed level. The present paper is motivated by this knowledge gap, both field tests and numerical simulations were conducted to help illustrate the basic characteristic of transient pressure loads, micro-pressure wave, as well as the wave propagation inside the tunnel regrading train's passage and intersection. Results present the major findings as: (1) Transient pressure loads acting at tunnel surface and train body unevenly distributes along the longitudinal, transverse, and vertical directions. Pressure peak along the longitudinal direction occurs nearly at tunnel center and fast decreases from the radiated center to the remote positions. (2) Variation of pressure peak near the tunnel portal in the situation of train's passage and intersection is limited while its value becomes doubled at the intersection location. Field measurements suggest the maximum pressure load acting at tunnel sidewall at x t i n = 200 m and tunnel center being 4.29 and 5.63 kPa, respectively; (3) The maximum value of micro-pressure wave (namely MPW) detected in the field test is approximately 36.73 Pa. Amplitude of MPW at tunnel portal is inversely proportional to its attenuated distance. Through data fitting, an empirical prediction model was established. Outcomes of this paper is anticipated to improve the understanding of tunnel aerodynamic effect regarding higher speed level and its associated problems. Besides, findings of this paper are useful for the future tunnel design. [ABSTRACT FROM AUTHOR]