Applied Mechanics and Materials Vols. 90-93

Abstract: Based on the one-dimensional unsteady compressible non-isentropic flow theory, micro-pressure wave radiated out of tunnel exit generated by a high-speed train entering a tunnel was investigated. In calculation process, the track roadbed and tunnel length were considered. The results, which were qualitatively and quantitatively analyzed, show that the ballast track has reduction effect of micro-pressure wave in long tunnel.

Abstract: Abstract. The compressive strength and elastic modulus of early-age shotcrete have important influence on the safety of tunnel during construction period. In order to investigate the laws of the mechanical properties of early-age shotcrete, experiments on the compressive strength and elastic modulus of early-age shotcrete with two different mixes used frequently on construction sites were carried out. The results show that the compressive strength and elastic modulus of shotcrete develop fairly rapidly and especially the development of elastic modulus of shotcrete is faster than that of ordinary concrete. There is an exponential relationship between the compressive strength and time as well as the elastic modulus development and time. Simultaneously their formulas were derived. The research results of this paper are not only helpful to understand the laws of the mechanical properties of early-age shotcrete, but also provide some reference for the reliability analysis of tunnel under construction.

Abstract: It is difficult to accurately identify dispersion curves of Rayleigh wave for the foundation with obstacles. Displacement curve of time-domain of half-space foundation have been obtained with the finite element in the paper. Then time-domain curve have been transformed Rayleigh wave dispersion curves. Rayleigh wave dispersion curves have been analysed in half-space foundation with water drain pipes. The results show that, there are reflection waves at the receiving signals in front of the obstacles, there are no reflection waves behind the obstacles basically. The location and spacing of the sensor have a greater impact on the results. The results provide the reference for the recognition of dispersion curves and disposition patterns of the sensors.

Abstract: To obtain the seismic responses of typical subway stations in Beijing, a nonlinear analysis was conducted using a pushover method for seismic analysis and design of underground structures. The analysis mainly focuses on stress in columns and side walls and relative displacement between top and bottom slabs under 3 different levels of PGA (peak ground acceleration). From the analysis, the column shows good ductility due to its high ratio of reinforcement, and it has a good performance under strong motions. Compared with columns, side walls suffer from brittle failure and lose bearing capacity prior to column for its lower ratio of reinforcement. The calculated displacement indicates that the relative displacement between top and bottom slabs is linear proportional to peak ground relative displacement (PGRD). And compared with peak ground acceleration (PGA), PGRD is a more reliable design parameter of ground motion for underground structures. And the typical subway stations in Beijng can withstand the earthquake with design PGA up to 0.2 g.

Abstract: The silty clay samples from Xiasha zone, Hangzhou city, are put into the reaction tank, which is specially made to investigate the diffusion characteristics of heavy metal copper ion. The silty clay is compacted, and then the solution with concentration of copper sulfate is 1762mg/L are added into one end of the tank. After laid for a time, several soil samples are cut from different positions in the tank, the adsorption contents of copper ion are tested. Experimental results show that the adsorption contents of copper ion in the silty clay decreases with the increase of the diffusion and movement distance. Besides, the relationship between the adsorption contents of copper ion and the diffusion and movement distance can be formulated as an exponential function.

Abstract: The studies carried out to appropriate slope ratio for underwater trench of immersed tunnel of Hongkong-Zhuhai-Macau Bridge. A test trench of 100-meter-long and 21-meter-width was excavated under Lingding Ocean along designed axis of immersed tunnel. The trench includes four slope ratio, such as 1:5, 1:6, 1:8 and 1:10. Two actual measurement which includes multibeam measurement and single beam double frequency measurement were used to measure water depth and section form in different time. It is recommended that slope ratio 1:6 can be adopted for underwater trench of immersed tunnel of HZM Bridge.

Abstract: The current calculation models of ground settlement for tunnel excavation cannot reflect ground settlement of tunnel non-synchronous excavation with double-line. Based on the Peck ground settlement formula and Attewell ground settlement formula, displacement release of excavation place and tunnel non-synchronous excavation with double-line have researched. By means of finding a function to replace the accumulated probability curve, the new control function was beneficial to parameter introduced and improvement of the current ground settlement formula. By introducing the non-synchronous excavation distance and the displacement release coefficient of excavation place, A new calculation model for ground settlement process of tunnels non-synchronous excavation with double-line is proposed. The reliability and practical of the calculation models was verified. Research results were very important to analyze the ground settlement affecting the building foundation and pipe under ground.

Abstract: The small spacing tunnel is a kind of tunnel structural style which situates between ordinary tunnel and double-arch tunnel. It has attracted great attention due to its unique merit. This paper takes Xiamen Airport highway tunnel as an example, considering four different construction steps during small spacing tunnel construction. Author applied MIDAS-GTS software to carry on numerical simulation, the influences of excavating orders of four different construction steps about stratum distortion and stable situation of middle rock pillar are analyzed. The analytical results indicate that construction Step 2 and construction Step 4 can suit actual situation of this project.

Abstract: In this paper a method for evaluating the slip speed in rolling contact is introduced from the contact mechanics viewpoint. Based on the analysis of the wear factors of the disc cutter, a theoretical model which includes disc cutter structural parameters and boring parameters is proposed to estimate the wear of the disc cutter in normal wear conditions. This theoretical model provides a basis for estimating the wear of the disc cutter and determining the replacing time of the disc cutter.

Abstract: For the cut and cover section of "framework + arch” modular structure of Xiamen Airport Road Project. Based on tunnel design section and other construction, technical requirements, we designed a 24.7 meters long and 13.5 meters wide framework loop wheel, with three rows of columns and complex structure and large cross section. In order to prevent to happen bias, two formwork loop wheel machines are symmetrical constructed.For the difference between outer ramp and main line, methods of filling soil and lengthening pillar are used. In order to reduce the load of the roof frame , scaffolding are installed. Obtained through the project monitoring, framework loop wheel machine meets the security requirements, and can improve construction speed and quality.