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.
This paper proposes an analytical model for evaluating the dynamic response of an underground railway tunnel in layered foundation soil with different saturations. The soil is modeled as layered ...media, and the circular tunnel lining is modeled as an infinite Flügge cylindrical shell. The separation of variables method is used to solve the motion equation of the shell, and the wave equation of the soil is solved using the Helmholtz decomposition theorem. A dynamic matrix reflecting the wave vectors of soil layers is established using the transfer matrix method. Based on boundary conditions, the tunnel-soil model is coupled using the transformation method of plane wave functions and cylindrical wave functions. The proposed model is validated by comparison with existing tunnel models, and the effects of saturation and the layered properties of soil on the dynamic response of a layered tunnel-soil system is demonstrated via case studies.
This study presents a comparative analysis of the deformation control effect of the hydraulic servo steel struts and ordinary steel struts of a foundation pit based on the measured axial force of the ...steel struts, lateral wall deflection, and ground surface settlement due to pit excavation. The results indicate that ordinary steel struts installed via axial preloading exhibit a disadvantageous axial force loss with a maximum value equal to 86.7% of the axial preloading force. When compared with ordinary steel struts, the hydraulic servo steel strut exhibits a superior supporting effect. The hydraulic servo steel strut adjusts the axial force in real time based on the deformation of the retaining structure and the axial force of the struts. Thus, the ratio of maximum lateral deflection to the excavation depth of a deep foundation pit in soft soil is less than 0.3%. Concrete struts undergo unsupported exposure during the excavation process, leading to sharply increasing deformation of the retaining structure. Therefore, regarding a foundation pit with strict requirements for deformation control, the use of hydraulic servo steel struts rather than concrete struts is recommended.
•The coupling effects between solid and fluid portions is considered in the analytical solution.•The surrounding soil can consider the variations of vertical displacements in both horizontal and ...vertical directions.•The research on floating piles is no longer limited to the assumption of semi-infinite space.•The proposed model can be degenerated to the condition of end-bearing pile.
Decades of high-speed railways operation around the world have revealed an increasing number of maintenance issues of pile-supported embankments subjected to long-term dynamic train loads in typical unsaturated soft soil areas. As the physical explanation of vibration characteristics of unsaturated soil piles is a theoretical basis for pile foundation design and pile integrity detection, a developed analytical solution of the vertical dynamic response of a floating pile in homogeneous unsaturated soils is proposed in this work. Based on the fictitious unsaturated soil pile (FUSP) model, the influence of saturation degree on soil shear modulus is considered in governing equations, uncoupled by using potential function and operator decomposition methods. The vertical dynamic response of a floating pile in a frequency domain is derived by employing the pile–soil compatibility conditions and the impedance function transfer method. Time-domain results are obtained by utilizing inverse Fourier transform and the convolution theorem. The correctness of the proposed model is verified by degradation to compare with the two existing solutions. Finally, a parameter study is undertaken to find the most sensitive parameters to the dynamic response of the floating pile in unsaturated soils.
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.
PurposeThis study establishes a method for predicting ground vibrations caused by railway tunnels in unsaturated soils with spatial variability.Design/methodology/approachFirst, an improved 2.5D ...finite-element-method-perfect-matching-layer (FEM-PML) model is proposed. The Galerkin method is used to derive the finite element expression in the ub-pl-pg format for unsaturated soil. Unlike the ub-v-w format, which has nine degrees of freedom per node, the ub-pl-pg format has only five degrees of freedom per node; this significantly enhances the calculation efficiency. The stretching function of the PML is adopted to handle the unlimited boundary domain. Additionally, the 2.5D FEM-PML model couples the tunnel, vehicle and track structures. Next, the spatial variability of the soil parameters is simulated by random fields using the Monte Carlo method. By incorporating random fields of soil parameters into the 2.5D FEM-PML model, the effect of soil spatial variability on ground vibrations is demonstrated using a case study.FindingsThe spatial variability of the soil parameters primarily affected the vibration acceleration amplitude but had a minor effect on its spatial distribution and attenuation over time. In addition, ground vibration acceleration was more affected by the spatial variability of the soil bulk modulus of compressibility than by that of saturation.Originality/valueUsing the 2.5D FEM-PML model in the ub-pl-pg format of unsaturated soil enhances the computational efficiency. On this basis, with the random fields established by Monte Carlo simulation, the model can calculate the reliability of soil dynamics, which was rarely considered by previous models.
Recently, servo steel struts have been increasingly used in deep foundation pits that require strict control over the deformation of the surroundings induced by excavation. However, the effects of ...strut length and axial force adjustments of servo struts on wall deflection and lateral earth pressure behind the wall are still unclear. In this study, a model excavation support system was constructed, and several model tests were conducted to investigate the effects of strut adjustments in which the axial forces and lengths of the struts were adjusted to various values. The strut axial forces, lateral earth pressure, and wall deflection were monitored and analyzed. The results show that: (i) the effects of the strut length and axial force on the lateral wall deflection vary with the depth of the adjusted struts. Adjustments of the struts at lower levels can reduce lateral wall deflections and effectively control the deformations. (ii) Increments in both the axial force and length of the struts result in lateral earth pressure changes between the at-rest and passive earth pressures in the vicinity of the adjusted struts. Neutral points can be observed during strut adjustments where the lateral earth pressures remain relatively constant. The locations and number of these neutral points varied depending on the depth of the adjusted struts. (iii) Simultaneous adjustments of the axial forces on multiple layers of struts are more effective in controlling lateral wall deflection than single-layered strut adjustments.
This paper presents a method for modeling the ground vibrations from a railway tunnel in layered unsaturated soil, considering the uncertainty and spatial variability of soil parameters. A ...deterministic ground vibration prediction model, which is an improved Euler beam model, is developed to evaluate the vibrations for a tunnel in layered unsaturated soil. Furthermore, the spatial variability of soil parameters is simulated by random fields using the Monte Carlo theory and the middle point method of Cholesky decomposition. By coupling the random fields of soil parameters to the deterministic vibration prediction model, the effect of uncertainty and spatial variability of soil on the ground vibrations is demonstrated through a case study. It is found that the variability of soil parameters has little influence on the spatial distribution regularities of ground vibrations, but it has a significant effect on the dynamic response amplitude and the critical velocity of the system.
Abstract
This paper proposes a reliability assessment method for environmental vibrations of a tunnel embedded in layered foundation under moving train load. Based on wave functions transformation, a ...vehicle-track-tunnel-soil model for evaluating system dynamic response can be established. Then combined with the Monte Carlo simulation, the reliability assessment of environmental vibrations is realized. The effect of soil parameter uncertainty on the prediction result of environmental vibrations is analyzed via case studies. The results show that the predictions from the deterministic model tend to be conservative, which is less than the superior limit of 95% confidence interval of the uncertainty model predicted outcome. The soil parameter uncertainty has less influence on the distribution of system dynamic response, which mainly affects the system dynamic response amplitude.
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•Seven fungicides with high detection frequencies (>85 %) were identified in three seasons.•Farmland density of controlled subbasin directly impact the spatial distribution of ...fungicides.•The reservoir affects fungicide transport, with retention effects in storage period.•Carbendazim is a substantial contributor to chronic ecological risk posed by fungicides.
As an indispensable type of pesticide, fungicides have been somewhat neglected compared to insecticides and herbicides. Heavy fungicide application in agricultural regions may generate downstream ecological concerns via in-stream transport, and the reservoir complicates the process. Monitoring fungicide exposure and exploring reservoir effect on fungicide transport is the key to develop the downstream strategies of agricultural diffusion pollution control. Here, we investigated the exposure, spatiotemporal dynamics, and ecological risk of fungicides in a reservoir-regulated agricultural basin, located in the middle of the Yangtze River Basin, China. Seven fungicides were preliminarily identified and exhibited high detection frequencies (>85 %) in subsequent quantification of water samples from three sampling activities. The total concentration of fungicides ranged from 2.47 to 560.29 ng/L, 28.35 to 274.69 ng/L, and 13.61 to 146.968 ng/L in April, September, and November, respectively. Overall, the contamination levels of fungicides were in the ascending order of April < November < September. The spatial distribution of fungicides was closely associated with the dense of cultivated land, supporting its agricultural source. Furthermore, the reservoir plays a retention role in fungicides, alleviating ecological pressure downstream during the water storage period. Yet, due to the alternation of “source” and “sink” function of the reservoir, the contribution of Zijiang River to the fungicide load in the Yangtze River Basin still needs further attention. Although there is no acute risk posed by fungicides, even in the high-exposure scenario, the chronic ecological risk could not be ignored. Agricultural intensive regions, coupled with the reservoir, provide rather substantial chronic ecological concerns. Carbendazim has been designated as a priority pollutant that contributes significantly to cumulative chronic risk. Thus, we emphasize strengthening the supervision of fungicides in surface water and rationally restricting the use of carbendazim in agricultural operations.
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