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This paper discussed the effect of different buried depth (B) of the twin-tunnels using scale experimental model and discrete element method (DEM). The diameter (D) of the twin-tunnels is 6.2 m, and the spacing between the two tunnels is 0.25 D. Five cosine functions are used to simulate the vibration load of the train passing through the first tunnel, which is very convenient to simulate the longitudinal movement of the train in two-dimensional DEM. In the 1/20 scale experimental model, self-made gypsum rings were used to simulate the tunnel liner, and the vibrator applied the train load. Surface uplift, the displacement and deflection of sleepers, as well as the displacement, velocity, acceleration and strain of the tunnel's liner and the surroundings are discussed with different buried depths twin-tunnels (0.5 D, 1.0 D, and 1.5 D). It is found that the buried depth of the tunnel will seriously affect the effect of train vibration on adjacent tunnels. The displacement, velocity, and acceleration in the vertical direction are much larger than the values in the horizontal direction. The deflection of sleepers during vibration will cause an unsafe run of the train in adjacent tunnel and pose risks to liner. It is suggested to build twin-tunnels with larger buried depth if the economy and technology requirements are satisfied. The research is expected to prove a reference for similar projects.

This paper presents a finite element analysis (FEA) of embedded concrete-filled steel tube (CFST) column-to-beam connections subjected to combined axial-flexural loading. The proposed FEA model was verified by experimental results from previous research. The comparison and analysis show that the predicted local damages, failure patterns, and load versus displacement curves were generally in good agreement with the experimental observations. Several identified parameters were studied, including various concrete strengths, steel tube yield stresses, embedded lengths, and axial loading ratios. Based on the parametric study, provisions and methods to estimate the effective flexural stiffness of the composite columns were suggested, and simple equations to estimate the effective stiffness of the whole connection were proposed. In addition, the fracture strain captured in the cyclic loading test was greater than that captured in the uniaxial tensile test. The inelastic responses of the CFST connections can be recorded using the FEA models, and the longitudinal strain can be used to define when tube tearing will occur, while the plastic equivalent strain can be used to define where tube tearing will occur.

The purpose of this paper is to develop a new method to improve the service life of asphalt pavement adding the geocell as reinforcement for asphalt mixture. A series of splitting fatigue tests were conducted and a viscoelastic damage model with clear physical meaning was used to evaluate the influence of geocell on the macroscopic performance of asphalt mixture. The test results show that the fatigue life of reinforced specimens is significantly improved compared to unreinforced specimens under the same loading conditions. Moreover, the improvement rate of fatigue life is not related to stress ratio, but related to loading temperature. When the loading temperatures are 5 °C, 15 °C and 25 °C, the improvement rates are approximately 60%, 110% and 230%, respectively. In addition, based on the viscoelastic damage model, it can be seen that the elastic modulus E v of the model increases with increasing stress ratio and decreases with increasing loading temperature, the model’s viscosity coefficients η e and η v both decrease with increasing stress ratio and loading temperature. The presence of geocell reduces the model’s elastic modulus E v and increases the viscosity coefficients η e and η v .

ZHANG Xiedong Ph.D Professor Wuhan University of Technology,Hubei, ChinaZhangxd@189.cnZhang Xiedong, born 1964, received his civil engineering doctor degree from the Wuhan University of Technology.The main 2D back analysis model is established considering actual situations of the way the arch ring is set and the composition of its section. After introducing the stress release rate and the load bias parameter to composing the integral equation of the influence value, the data of arch crown settlement and horizontal convergence can be used to back analyse the load status of the supporting structure. By changing the modeling parameters, the optimizing construction scheme can be simulated and the most unfavorable stress value is analyzed, which can provide references to similar engineering.