Chenghua Shi

Face stability analysis of shallow underwater tunnels in fractured zones

When an underwater tunnel constructed via the mining method crosses a fault fracture zone, one of the most important issues to consider is ensuring the stability of its face. Several auxiliary techniques have been adopted in construction; however, the design parameters of these auxiliary measures are mainly determined by experience. In this study, a stability analysis model of the working face of an underwater tunnel constructed via mining method in a fractured zone was established by considering the effect of groundwater seepage force. Afterward, the corresponding formula was determined. By considering a pre-support pipe roof and an advanced grouting ring as a beam on the elastic foundation, the corresponding stability analysis model and computing method under pre-reinforced condition were built. In addition, an engineering example was analyzed. Results show that the stability coefficient of the tunnel face is only 0.77 without the pipe roof and advanced grouting. Meanwhile, the stability coefficient increases to 2.47 under pre-reinforced condition. This finding indicates that a tunnel must be reinforced in advance in a fractured zone to ensure safe construction. The influences of pre-reinforcement parameters (i.e., thickness, cohesion, and internal friction angle of the grouting circle) on the stability of the tunnel face are discussed at the end of the article.

Modified chloride diffusion model for concrete under the coupling effect of mechanical load and chloride salt environment

For the purpose of investigating lining concrete durability, this study derives a modified chloride diffusion model for concrete based on the odd continuation of boundary conditions and Fourier transform. In order to achieve this, the linear stress distribution on a sectional structure is considered, detailed procedures and methods are presented for model verification and parametric analysis. Simulation results show that the chloride diffusion model can reflect the effects of linear stress distribution of the sectional structure on the chloride diffusivity with reliable accuracy. Along with the natural environmental characteristics of practical engineering structures, reference value ranges of model parameters are provided. Furthermore, a chloride diffusion model is extended for the consideration of multi-factor coupling of linear stress distribution, chloride concentration and diffusion time. Comparison between model simulation and typical current research results shows that the presented model can produce better considerations with a greater universality.For the purpose of investigating lining concrete durability, this study derives a modified chloride diffusion model for concrete based on the odd continuation of boundary conditions and Fourier transform. In order to achieve this, the linear stress distribution on a sectional structure is considered, detailed procedures and methods are presented for model verification and parametric analysis. Simulation results show that the chloride diffusion model can reflect the effects of linear stress distribution of the sectional structure on the chloride diffusivity with reliable accuracy. Along with the natural environmental characteristics of practical engineering structures, reference value ranges of model parameters are provided. Furthermore, a chloride diffusion model is extended for the consideration of multi-factor coupling of linear stress distribution, chloride concentration and diffusion time. Comparison between model simulation and typical current research results shows that the presented model can produ...

Numerical Simulation about Train Wind Influence on Personnel Safety in High-Speed Railway Double-Line Tunnel

According to the 100m 2 double-line tunnel cross-section which is generally used in high-speed railway of China, this paper develops a tunnel - air - train simulation model, based on the three-dimensional incompressible Navier - Stokes equations and the standard k − e turbulence model. This model can simulate two situations one is that a single train runs through a tunnel normally while the other is that another train runs beside a train parked in the tunnel. Time-history variation rules and space distribution characteristics of train wind are studied respectively at 120 km, 200 km, 250 km, 300 km and 350 km per hour. Furthermore, the authors discuss train wind influence on personnel safety on evacuation passageways. In addition, the authors give out analytically the results of the numerical simulation. The results show that: Train wind is complex three-dimensional flow changing with time and space, so people should avoid activities at dangerous time and places; since personnel safety may be threatened by train wind in the two situations above, therefore, effective measures should be taken to avoid accidents.

Research on the construction risk control technology of shield tunnel underneath an operational railway in sand pebble formation: a case study

It’s inevitable that, various types of construction works emerge within proximity during the large-scale construction of urban rail transit, thus posing huge challenges for the actual construction....

A Structural Calculation Model of Shield Tunnel Segment: Heterogeneous Equivalent Beam Model

A heterogeneous equivalent beam model (HEB model) of the shield tunnel segment structure is proposed based on a systematical analysis on the stress state of the cross section of segment joints. This model treats a noncontinuous segment structure as a continuous heterogeneous structure, on the basis of the principle of equivalent stress state on a section and equivalent conversion of the mechanical parameters. For a comprehensive demonstration of the proposed HEB model, an interpretative solution of equivalent mechanical parameters of the joint section is obtained through theoretical derivation, and a specific iterative computation flow is provided in accordance. Model validation and comparative analysis are also conducted for two industrial applications. It is found that the iterative process of calculation has good convergence, leading to reliable numerical results for all cases under consideration. Resulting simulations reveal that the proposed HEB model can reflect the effect of joints on overall rigidity of a segment structure. Compared with the computation results obtained using other models presented in the literature, there are smaller axial force deviation and larger bending moment deviation (up to 20% or higher), demonstrating that the model selection is important in design and computation of a segment structure of shield tunnels. The proposed model and analysis for model performance may provide useful reference for engineers in shield tunnel community.