Mingfeng Lei

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.

Accumulated Deformation Behavior and Computational Model of Water-Rich Mudstone Under Cyclic Loading

With the rapid development of Chinese railway systems, a large number of railway tracks have been built on or across soft soils and soft rocks, resulting in problems such as accumulated deformation and settlements of the tracks (Zhang et al. 2009) and severe mud pumping in railway tunnels which are built through soft soils (Zhu and Li 2001). Such problems are a big challenge to the safety and efficiency of train operation. Investigations on the characteristics of long-term deformation of geotechnical materials under cyclic train loading are of great interest in engineering practice. Sangrey and Henkel (1969) conducted triaxial cycling tests for saturated soft clay and demonstrated the existence of a critical stress state for soils. Yasuhara and Yamanouchi (1983) performed a triaxial drained test on soft soils under cyclic loading. Muhanna (1994) reported that the permanent deformation of soils was proportional to the cyclic loading number and stress level. Jafari et al. (2004) conducted a systematic study on the fatigue behavior of artificial rock joints that were subjected to cyclic shearing. Bagde and Petros (2005, 2009) analyzed the fatigue behavior of intact sandstones under dry and saturated conditions with dynamic uniaxial cyclic loading. Erarslan and Williams (2012) studied the stress–strain characteristics of Brisbane tuff disc specimens under a diametral compressive sinusoidal cyclic loading with an increasing magnitude. Chinese researchers have also conducted extensive research in this area. Several cyclic triaxial tests have been conducted with different soil types. Systematic studies have been conducted to evaluate the characteristics of cyclic deformation and identify their influencing factors (Cai and Cao 1996; Tang et al. 2003; Gong et al. 2009). Several empirical models based on the results of cyclic loading tests have been developed to describe the cyclic cumulative deformation behaviors of different geotechnical materials. Monismith et al. (1975) proposed an exponential model for the cumulative plastic deformation of clay under cyclic loading. Li and Selig (1996) improved Monismith’s model by adding soil static strength parameters. Based on these models, Chai and Miura (2002) proposed a computational formula to predict the cumulative deformation of road subgrade soil under traffic loading. This formula, which takes into account the original state of soil, is expressed as

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...

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.