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Abstract: This paper provides an in-depth illustration of the shallow tunnelling method (STM) used for tunnelling in shallowly buried soft ground. Limited arching effect and limited ground strength mobilization are the two mechanical characteristics of the STM. The stability of the cutting face and the dry tunnelling condition are the two preconditions that should be satisfied for the STM. Some “necessary” auxiliary methods mainly served to guarantee these two preconditions are highlighted. Five principles, namely proper auxiliary methods, sequential excavation with short advance length, rigid support with quick installation, short ring closure time and systematic deformation monitoring, which are required to follow when using the STM are summarized. The state-of-art of the STM is classified into five different construction approaches according to tunnelling sequences, which are adopted in the construction of the nine subway stations in Beijing. The tunnelling procedures, support measures and settlement characteristics associated with excavation are demonstrated. Statistical analyses of the settlement data of 342 ground surface monitoring points above these nine stations are performed to illustrate the ground deformation characteristics of the STM. Numerical simulations are also employed to study the ground deformation characteristics of different construction approaches under the same geological conditions. This paper systematically demonstrates the applicability of STM in theory and practice. It is helpful in updating the database of the world tunnel projects and serving as a practical reference for future similar projects. [Copyright &y& Elsevier]

• A two-way coupled method was used of 166.6 MHz superconducting coupler. • The two-way coupled method is electromagnetic-fluid-thermal coupled method. The improved design reduces the risk of quench, while reducing heat leakage. Five 166.6 MHz beta = 1 quarter-wave resonator (QWR) superconducting cavities (SC) have been chosen for the High Energy Photon Source (HEPS), a 6 GeV kilometer-scale diffraction-limited storage light source to be built in Beijing suburb. Each cavity is equipped with one high power input coupler to deliver over 180 kW RF power in continuous mode (cw). Overheating and the result in excessive heat load, even quench were observed during the horizontal test of the first proof-of principle (PoP) cavity. To find the overheating reason, a dedicated two-way coupled electromagnetic-fluid-thermal simulation of the helium gas-cooled coupler was carried out by Ansys solver. This paper presents some key parameters of the coupler calculated by the two-way coupled electromagnetic-fluid-thermal numerical simulation and the accuracy of the simulation was proved by comparing with the horizontal test results. Based on the electromagnetic-fluid-thermal coupling analysis, this paper takes into account the inlet gas temperature and flow rate on the temperature distribution, electromagnetic loss distribution, and 4.2 K heat load of the coupler. Furthermore, the occurrence conditions of overheating and quench are explored and some improvement suggestions of the coupler structure are given. [ABSTRACT FROM AUTHOR]

Recent studies have provided that the vehicle trajectories generated by car-following models may not represent the real driving characteristics, thus leading to significant emission estimation errors. In this paper, two of the most widely used car-following models, Wiedemann and Fritzsche models, were selected and analyzed based on the massive field car-following trajectories in Beijing. A numerical simulation method was designed to generate the following car’s trajectories by using the field trajectories as the input. By comparing the simulated and the filed data, the representativeness of the simulated regime fractions and VSP distributions were evaluated. Then, the mechanism of car-following models was investigated from the aspects of regime determination and the acceleration rule in each regime. Further, the regime threshold parameters and acceleration model were optimized for emission estimations. This study found that the “Following” regime threshold of SDX and the maximum acceleration in “Free Driving” regime are critical parameters for Wiedemann model. The differences between the Wiedemann simulated VSP distribution and the field one can be reduced separately by applying the optimized SDX and maximum acceleration model individually. However, a much sharper reduction was observed by optimizing both parameters simultaneously, and the emission estimation errors were further reduced, which were less than 4% in the case studies. Fritzsche model generated more realistic VSP distributions and emissions, while the maximum accelerations could be further optimized for high speed conditions. [ABSTRACT FROM AUTHOR]

In this paper, a numerical method of the rising groundwater level is presented through an elastoplastic constitutive model for the unsaturated soil and a numerical realization method for the rising groundwater level. A model test of the rising groundwater level is conducted to validate the rationality of the presented numerical method. Taking an interval subway tunnel in Beijing as the background, a numerical simulation with a homogeneous soil layer, which contians the existing tunnel, is conducted according to the presented numerical method of the rising groundwater level. Based on the numerical simulation results, the variations of the ground saturation, the ground stress state, and the ground vertical deformation under the condition of the rising groundwater level are studied through a homogeneous soil layer, and the normal contact pressure on the outer surface of the lining, the radial deformation, the bending moment, the hoop thrust, and the shear force of the lining under the condition of the rising groundwater level are analyzed through a homogeneous soil layer with the existing tunnel. [ABSTRACT FROM AUTHOR]