Search

This article investigates the size effect of segmental tunnel linings on the deformation behavior and the damage evolution mechanism using the Finite Element Method (FEM). A series of models with different diameters are established under the same loading condition to control the variable. The bolts and the rebar apply the elastic-plastic model. The Concrete Damage Plasticity model has been considered for the concrete lining. The vertical convergence deformation, internal force of these models, and damage to the segment body are selected for comparison. The number and location of the yielded bolts are explored for the analysis of the overall structure stiffness and damage evolution mechanism. In terms of plastic hinge theory, an extended discussion is carried out to explain the differences in damage evolution mechanisms in different-sized linings. The results show the large-diameter lining rings have a relatively greater increasing rate of convergence deformation. Furthermore, fewer plastic hinges emerged in large-scale lining rings before the structures reached their ultimate strength. According to the experimental results, we can know that the failure of large-diameter has the characteristic of more brittle damage than that of small-diameter one and these large-size structures are prone to become unstable geometry. [ABSTRACT FROM AUTHOR]

In order to better interpret failure features of the failure of soil in front of tunnel face, a new three-dimensional failure mechanism is proposed to analyze the limit support pressure of the tunnel face in multilayered cohesive-frictional soils. The new failure mechanism is composed of two truncated cones that represent the shear failure band and a distributed force acting on the truncated cones that represents the pressure arch effect. By introducing the concept of Terzaghi earth pressure theory, approximation of limit support pressures is calculated using the limit analysis methods. Then the limit support pressures obtained from the new failure mechanism and the existing approaches are compared, which show that the results obtained from the new mechanism in this paper provide relatively satisfactory results. [ABSTRACT FROM AUTHOR]

The face stability of a circular tunnel in cohesive–frictional soils was numerically and theoretically investigated. Three-dimensional (3D) numerical simulations were first performed to analyze the face stability of a circular tunnel with a series of tunnel diameter-to-depth ratios and soil properties. The limit support pressure on the tunnel face and the failure zone in front of the tunnel face were both obtained from the numerical simulations. A simple and feasible criterion was suggested to outline the boundary strip of the failure zone at collapse in displacement clouds under different conditions. Based on the numerical simulation results, a new 3D failure mechanism was proposed using the kinematic approach of limit analysis theory to determine the limit support pressure of the tunnel face. The new 3D failure mechanism was composed of four truncated cones on which a distributed force acts. Finally, the limit support pressures and failure zones obtained from the new failure mechanism and the numerical simulations were compared. In addition, comparisons between the results of this work and those of existing approaches were performed. Overall, the new failure mechanism is substantially more consistent with the shapes of the failure zones observed in numerical simulations and experimental tests than the existing multi-block failure mechanisms. The new failure mechanism is more effective and reasonable. [ABSTRACT FROM AUTHOR]

The issue of tunnel face stability traversing the fault fracture zone with high hydraulic pressure has been addressed based on a new three-dimensional limit equilibrium model. First, the finite element numerical simulation is conducted to reveal the effects of the differences in permeability coefficient of strata on both sides of the geological interface on the distribution of seepage flow field nearby tunnel face. With this discovery, an existing universal approximate formula for hydraulic head nearby tunnel face is modified to accurately calculate the hydraulic head distributions under this scenario. Second, introducing the effect of geological interface, a new limit equilibrium model that consists of a trapezoid and a prism is proposed. The distributed loading exerted by the prism upon the trapezoid is deduced by considering the effects of seepage force and geological interface. Then, limit support pressure is derived according to the limit equilibrium state of the trapezoid. Finally, the comparison of the predicting results of the proposed limit equilibrium model with the results of the numerical simulations and the existing failure mechanism is performed, which indicates that the proposed trapezoid-prism model can well predict the tunnel face stability traversing the fault fracture zone with high hydraulic pressure. [ABSTRACT FROM AUTHOR]

In this paper, numerical simulations of face stability of shallow tunnels are carried out by using the particle discrete element codes PFC2D from the microscopic view. Progressive instability of the tunnel face is achieved through the withdrawal of the baffle used to simulate the tunnel face. Under different retreating displacement of the tunnel face, the evolution laws of support pressure on the tunnel face, the ground deformation, ground surface settlement and contact force chain in front of the tunnel face are studied. The results show that with the withdrawal of the tunnel face, the support pressure on the tunnel face can be divided into four stages, namely, the rapid decline stage, the minimum stage, the slow rising stage, and the horizontal stability stage. Moreover, based on the simulation results of the particle contact force chain, discriminated methods of failure zones are proposed. The research results obtained from this paper will provide theoretical support for the reasonable value of support pressure of a tunnel face in practical engineering. [ABSTRACT FROM AUTHOR]

When tunnels are constructed under difficult geotechnical conditions in urban areas, tunnel face stability is one of the main issues to be addressed. To ensure tunnel face stability and reduce the impact of tunneling on adjacent structures, a few alternative procedures of ground reinforcement should be adopted, which includes reinforcing the soil ahead of the face using longitudinal fiberglass dowels alone or together with a steel pipe umbrella. It is of great academic value and engineering signification to reasonably determine the limit reinforcement density of these ground reinforcements. In this paper, an analytical prediction model is proposed by using the limit analysis method to analyze the tunnel face stability, and the favorable effects of longitudinal fiberglass dowels and steel pipe umbrella on tunnel face stability are investigated quantitatively. The analytical prediction model consists of a wedge ahead of the tunnel face, distributed force acting on the wedge exerted by overlying ground, and the support forces stem from the longitudinal fiberglass dowels. Moreover, sensitivity analysis is conducted to study the effect of the depth of cover, the tunnel shape, the reinforcement installation interval and the reduction factor on the required limit reinforcement density. [ABSTRACT FROM AUTHOR]

Heat-treated high-strength rebar has many advantages, such as high strength, superior ductility, high yield ratio, excellent welding and cold bending performance, which can effectively reduce the amount of rebar and improve the project quality. Although heat-treated high-strength rebar has been successfully applied in many fields of civil engineering, its application in tunnel engineering is just getting started. In this study, the on-site test of axisymmetric heat-treated high-strength lattice girders in rail tunnels and road tunnels was carried out. Comparative analysis of the performance of axisymmetric heat-treated high-strength lattice girders and original-design I20b steel rib was conducted. The test results show that the settlement of high-strength lattice girders is decreased by about 7%~30% compared with the test section of original-design I20b steel rib. The surrounding rock pressure is similar, but the stress of high-strength lattice girders is slightly higher than that of I20b steel rib. Due to the better binding ability of the lattice girders and the concrete, the ultimate bearing capacity of the 'lattice girders and shotcrete' is greater than that of the 'I20b steel rib and shotcrete'. Moreover, the steel consumption of lattice girder is about 36% less than I20b steel rib, which shows significant economic and social benefits. [ABSTRACT FROM AUTHOR]

• Investigates the progressive failure phenomenon of the shallow tunnel roof by virtue of the functional catastrophe theory. • The failure mechanism proposed can not only predict the 'underground' collapse but also the 'spalling' collapse. • The comparisons of the results between analytical predictions are validated. Collapse mechanism for the tunnel or underground cavern is important for the support system design. This paper investigates the progressive failure phenomenon of the shallow tunnel roof under the condition of plane strain by virtue of the functional catastrophe theory. Firstly, considering the plastic strain energy as an index for the state of the studied system, the analytical solutions for the profile curves of the collapsing blocks from the shallow tunnel roof including the 'underground' collapse and 'spalling' collapse are deduced on the basis of the nonlinear power-law failure criterion. Moreover, the criterions are derived to estimate whether the progressive failure phenomena including the 'underground' collapses and 'spalling' collapses for shallow tunnel roof would occurr or not. Then, the analytical prediction obtained from this paper for the shallow tunnels is compared with the existing analytical prediction for the deep tunnels. Finally, the comparisons of the results between analytical prediction obtained from this paper and two existing model tests are conducted to demonstrate the validity of the proposed analytical methodology. [ABSTRACT FROM AUTHOR]

Numerical simulation of segmental lining tunnel subjected to internal explosive loading is carried out in this paper based on the arbitrary-Lagrangian-Eulerian (ALE) and finite element (FE) coupled algorithms. A high-fidelity FE model considering assembled features of segmental lining structure is established, and the mapping technique is adopted to accurately simulate the explosion process. The calculated overpressure histories and failure modes of the lining structure fit well with field test results of full-scale specimens, indicating the applicability and accuracy of the numerical model. A more comprehensive numerical model considered the practical service state of segmental lining tunnel is further built based on the verified model. Influences of mechanical properties and pressure levels of surrounding soils on dynamic responses of tunnel structure under internal explosion are investigated. Numerical results show that dominated deformation modes of the segmental lining tunnel under the action of internal explosion include opening deformation at the segmental joints of the charged ring and shear deformation between the adjacent rings. The modest explosion caused by terrorist bombing attacks may severely harm the shield tunnel structure and impair its service performance, especially if the tunnel is buried in soft soil at a shallow depth • Numerical simulation of segmental lining tunnel subjected to internal explosive loading is conducted. • The accuracy of numerical simulation is verified by comparison with field test. • Mapping technique is adopted to accurately simulate the explosive load. • Dominated deformation modes of segmental lining tunnel under internal explosion are analyzed. [ABSTRACT FROM AUTHOR]

• A multistage resilience analysis model for tunnel lining was proposed. • Diameter convergence and settlement were selected as performance indicators. • Classification standard for resilience of tunnel lining was defined. The assessment of shield tunnel linings is a key activity for ensuring the operational safety of trains. This paper proposed an analytical model for evaluating the resilience of shield tunnel linings considering multistage disturbances and recoveries on the basis of resilience theory. The resilience metric of the tunnel linings was calculated according to a multistage resilience analysis model established by this paper. The diameter convergence and settlement of the tunnel were chosen as the performance indicators based on the different responses of the tunnel linings under loading and unloading conditions. The classification standard for the resilience of the tunnel linings was suggested according to existing research results. Then, the influences of the performance recovery degree and decision-making time on the tunnel linings resilience were discussed. Finally, the analytical model proposed in this paper was applied to the case of basement excavation beside existing tunnels. The results showed that the resilience metric obtained by different linings performance indicators was obviously different. For excavation beside existing tunnels, only taking diameter convergence as the performance indicator of the tunnel linings caused the calculation results to be high, that is, the linings resilience was overestimated. From the case in this paper, the settlement of the tunnel should be given more attention. In addition, the existence of the evolution stage in the performance degradation curve significantly reduced the resilience of the tunnel linings. The research results in this paper will provide important references for the safety assessment of shield tunnels and the performance recovery of damaged linings. [ABSTRACT FROM AUTHOR]