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An analytical model for predicting the vibrations from an underground railway tunnel embedded in an unsaturated half-space is proposed. The tunnel lining is modeled as an infinite Flügge cylindrical shell, and the unsaturated soil is modeled as a three-phase medium comprising solid grains and pores containing water and air. By using the transformation properties between the plane wave functions and the cylindrical wave functions, the model is coupled based on the boundary conditions. The developed model is validated by comparison with existing tunnel models, and the effect of saturation on the dynamic response of the tunnel–soil system is demonstrated through a case study. [ABSTRACT FROM AUTHOR]

In this paper, areas of soil disturbed by pipe jack construction are categorized and analyzed in detail. Mechanisms of soil disturbance are discussed and patterns of soil deformation are studied using random medium theory. Lateral deformations in deep soil, pore water pressures, stratified settlement, and earth pressures are investigated using measurements from an electrical transmission pipeline project in China. The measurements show that soil layer movement can be predicted by monitoring changes in pore water pressure, and the amplitude of soil disturbance transverse to the pipeline is larger than that above the pipeline in this project. The distributions of stress components in the direction of, and vertical to, the pipeline axis are studied by numerical simulation. It shows that the closer to the pipeline axis, the greater the additional stress, the faster the attenuation speed, and the smaller the range of influence. Relationships of positive propulsion, friction, and stratum loss with longitudinal and transverse surface deformations are also discussed. The ground displacement is a coupling of the three factors to the action of the soil. The surface transverse subsidence with a main influence range of about ±4 D (D is outer diameter of pipe jacking). The findings from this study can be used as technical foundation and reference for the construction of similar projects. [ABSTRACT FROM AUTHOR]

This study investigated several ground collapses in sandy cobble strata induced by shield tunneling in two intervals of Lanzhou Metro Line 1 and proposed corresponding control measures. Ground collapses were classified into three types (A, B, and C). The distribution of low-compactness zones was the primary cause of the collapses that occurred after steady excavation (A-type), indicating that advanced grouting should be conducted beneath these zones. The grouting area should be a semi-circular ring in the transverse section, with a grouting ring height and thickness of 1.05 m and 0.51 m, respectively. A poor tunneling state caused by fluidity reduction in the cutter chamber was the main reason for collapses caused by restarting the shield after long-term shutdown (B-type). We suggest rotating the cutterhead every 12 h during long-term shutdown and supplementing the bentonite until the cutterhead torque falls below 3500 kN·m. Collapses caused by cutterhead blockage (C-type) were mainly due to encountering large boulders during tunneling. We suggest pulling the front shield back with hinge equipment when the cutterhead is blocked, with a backward distance greater than the penetration distance (35 mm) and a face pressure above the limit support pressure calculated using the method presented in this paper. [ABSTRACT FROM AUTHOR]

This paper presents a landslide that occurred in loess hills resulting in structural damage to the Zhangjiazhuang tunnel of the Lanzhou–Xinjiang high-speed railway line. The characteristics of tunnel deformation and structural damage are provided in detail. To ensure future safety of the tunnel, investigations consisting of field reconnaissance, borehole investigations, seismic activity and rainfall records analysis, and numerical simulations were conducted to identify the regional geology and landslide characteristics. Using these investigations, the probable formation mechanism of this sliding failure is determined to be (i) an ancient groove that provides a natural slip bed leading to stress concentrations and dislocation failure at the back of the slope; (ii) seepage channels that are well-developed on this loess hillslope, through which an extreme rainfall event 6 months prior to the landslide saturated the strata materials; and (iii) finally, the limit state of the materials is reached in an earthquake under undrained condition, and the landslide is triggered. The findings presented in this paper can provide a reference for the control and treatment of landslides in loess areas. [ABSTRACT FROM AUTHOR]

Construction issues of high-speed rail infrastructures have been increasingly concerned worldwide, of which the subgrade settlement in soft soil area becomes a particularly critical problem. Due to the high compressibility and low permeability of soft soil, the post-construction settlement of the subgrade is extremely difficult to control in these regions, which seriously threatens the operation safety of high-speed trains. In this work, the significant issues of high-speed railway subgrades in soft soil regions are discussed. The theoretical and experimental studies on foundation treatment methods for ballasted and ballastless tracks are reviewed. The settlement evolution and the settlement control effect of different treatment methods are highlighted. Control technologies of subgrade differential settlement are subsequently briefly presented. Settlement calculation algorithms of foundations reinforced by different treatment methods are discussed in detail. The defects of existing prediction methods and the challenges faced in their practical applications are analyzed. Furthermore, the guidance on future improvement in control theories and technologies of subgrade settlement for high-speed railway lines and the corresponding challenges are provided. [ABSTRACT FROM AUTHOR]

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The disc cutter of tunnel boring machines (TBMs) intended for sandy cobble strata undergoes severe wear, which significantly increases the cost and construction period. Currently, there is no wear prediction model for disc cutters in the case of sandy cobble strata. This paper proposes a wear prediction model for disc cutters of a TBM operated in sandy cobble strata. A wear rate expression is determined based on the theory of tribology. A quantitative relationship between the wear coefficient and the particle size parameters (Cu and d60) is established. The strength of the cobbles and the motion track and outline of the disc cutter are considered in the model. The model is validated using field data from two cases. The effect of grain distribution is considered in the proposed model, unlike that in existing prediction models, thus offering a more effective approach in predicting the wear of disc cutters intended for sandy cobble strata. [ABSTRACT FROM AUTHOR]

Jet grouting piles were widely employed for ground reinforcement in building and infrastructure engineering due to the low cost and construction convenience. However, this foundation treatment method is not allowed to be used in high-speed railway involved constructions in China because of the concerning of the negative effect on the lateral displacement of the existing high-speed railway. To find a reasonable application distance of jet grouting piles away from existing high-speed railway bridge in deep soft soils with medium sensibility, a series of laboratory and in-situ tests on the influence of the jet grouting piling on the deformation of surrounding soils and adjacent high-speed railway bridge are carried out. The geological characteristics of the construction site and the mechanical properties of the soft soil are deeply investigated by utilizing field and laboratory tests. The piling induced lateral displacement of the surrounding soils is monitored as well as the displacement of an adjacent high-speed railway bridge. The monitoring data reveal that the influence area of the jet grouting piling is approximately 1.75 ∼ 1.85 times of the pile length in deep soft soils. The critical distance of the jet grouting piles from the existing high-speed bridge should be larger than 2 times of the pile length. [ABSTRACT FROM AUTHOR]

Ferroelectric domains of the tetragonal (Pb[sub 0.985]Bi[sub 0.01])(Ni[sub 1/4]Zn[sub 1/12]Nb[sub 2/3])[sub 0.2](Zr[sub σ]Ti[sub 1-σ])[sub 0.8]O[sub 3] (σ=0.30 and 0.40) ceramics were investigated by transmission electron microscopy and electron diffraction. It was observed that the 90° macrodomains displayed the shape of simple lamella twinning, and that the δ-fringe contrast was frequently observed within these configurations of 90° domains. The 180° domain walls with zigzag structure between 90° domain walls were also observed. The formation sequences of the 90° and 180° domain structures were discussed in terms of energy minimization during the phase transition from cubic to tetragonal ferroelectric phase on cooling. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

• An accurate and efficient model is presented to predict the dynamic responses from underground tunnels. • The effect of the tunnel ring joint stiffness on the ground vibrations is investigated. • The effect of the tunnel ring joint stiffness on the dynamic responses of foundation soil is investigated. • The effect of the tunnel ring joint on soil vibrations under different thicknesses of tunnel ring is investigated. The vast majority of underground tunnels are constructed by the shield-driven method, resulting in the tunnel structure being periodically jointed in the longitudinal direction. Significant studies have been proposed to predict vibrations from a homogeneous tunnel, while less attention has been paid to the effect of the tunnel ring joint and its stiffness property. This paper develops a new three-dimensional analytical model to investigate the influence of the ring joint stiffness on the dynamic responses from underground tunnels. The solution for a harmonic moving load applied to the periodic jointed tunnel is derived by using the periodic-infinite structure theory. The solution for wave propagation in the saturated porous medium is developed by the Biot's theory and potential decomposition. By using the wave transformation, the periodic jointed tunnel is coupled with the saturated soil via the boundary conditions on the tunnel-soil interface. This model is validated via the comparison with existing solutions. Numerical results for a moving harmonic load applied to the periodic jointed and homogeneous tunnels are analysed in detail. It is found that the tunnel ring joint stiffness has a significant effect on the soil vibration levels, indicating that the tunnel ring joint and its stiffness property should be considered in the prediction of ground vibrations induced underground railways. [ABSTRACT FROM AUTHOR]

The vast majority of existing underground railway lines consist of twin tunnels. However, most previous studies on the prediction of vibrations induced by underground railways only considered a single tunnel. This paper presents a semi-analytical model for the dynamic interaction between twin tunnels in a multi-layered half-space. Multiple scattered waves are generated by the two cylindrical cavities, layer interfaces, and ground surface in such a complex model that cannot be solved theoretically by the method used for a single–tunnel model. In this regard, the translation between two different cylindrical waves is first introduced. Combining the transfer matrix method and the transformation between plane and cylindrical waves, the solution for the dynamic interaction between twin tunnels in a multi-layered half-space is obtained by means of the boundary conditions at the tunnel–soil interfaces. The accuracy of the proposed model is evaluated by comparing with the existing numerical models. The train-induced vibrations from twin tunnels embedded in a multi-layered half-space are subsequently investigated by coupling the proposed model with a vehicle–track model. The numerical results demonstrate that the existence of a neighbouring tunnel has a significant effect on the ground vibrations. [ABSTRACT FROM AUTHOR]

Abstract The majority of existing subway tunnel lines are constructed by the shield method, which is assembled by several segmental linings connected by joints. However, the previous studies on the prediction of vibrations from underground railways mostly considered the tunnel as a closed homogeneous ring. This paper proposed a two-and-a-half-dimensional (2.5-D) finite element-boundary element (FE-BE) methodology to investigate the dynamic response of a segmented tunnel in the saturated soil. The segmental linings and connecting joints are simulated as 3-D isotropic elastic solids and a set of springs by the 2.5-D FE method, respectively. The surrounding soil is modelled by the 2.5-D BE method for a saturated porous medium. The 2.5-D FE method and the 2.5-D BE method are then coupled via the boundary conditions on the tunnel–soil interface. Numerical results show that a homogeneous tunnel model underestimates the dynamic stress and pore-water pressure in the foundation soil. The influence of the tunnel joint on the vibration level of the ground surface highly depends on the load frequency. Highlights • To present a numerical model for the calculation of dynamic response of a segmented tunnel in the saturated soil. • To analyze the influence of the tunnel joint on the soil stress and pore-water pressure of the foundation soil. • To analyze the influence of the tunnel joint on the vibration of the ground surface. [ABSTRACT FROM AUTHOR]

Given their high cost, servo steel struts typically are used only in specific sections of foundation pits in which nearby buildings are sensitive to excavation-induced deformation. Servo steel strut adjustments affect the mechanical behaviors of adjacent ordinary-steel-strut-supported areas. However, the plane strain assumption is used in current designs, ignoring this influence. To propose a more reasonable design, the effects of servo steel strut adjustments should be examined. In this study, a model support system with adjustable strut axial forces was constructed (scale: 1∶20 , under 1g), and several groups of tests with different adjustment schemes were conducted. The lateral earth pressure, lateral wall deflection, and strut axial forces were monitored and analyzed. The results indicated the following: (1) the first level of struts is not suitable to be actively adjusted because this can increase the maximum lateral wall deflection; (2) increasing the strut axial forces can lead to redistribution of lateral earth pressure along the horizontal direction, which can be divided into two areas with different characteristics, and whereas the lateral wall deflection decreases in both areas, the lateral earth pressure increases in the area adjacent to the adjusted strut and decreases in the other area; and (3) a transition section can be designed between the servo-steel-strut-supported area and the ordinary-steel-strut-supported area, within which strut adjustment diminishes as one approaches the ordinary-steel-strut-supported area. However, the horizontal length of the transition section should exceed a threshold value, which is approximately 3 times the horizontal strut distance, to effectively mitigate the axial force reduction in ordinary steel struts. [ABSTRACT FROM AUTHOR]