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High-speed railway embankments are the supporting body of a train and track and are directly exposed to complex climate conditions, such as rainfall, evaporation, and other environmental events. These conditions change the water content, suction, and shear strength of embankment-filling soil, thereby affecting the stability of an embankment. This paper devises a coupled moisture–heat flow model for unsaturated soil embankments that considers soil–atmosphere interactions. The model is verified by comparison of data it generates with the data measured at a highway embankment in Rouen, France. Moreover, based on the actual meteorological data of two cities in China (Beijing and Shanghai), the moisture response of a high-speed railway embankment is calculated to investigate the effects of climate conditions and soil types. This reveals that the degree of saturation at shallow depths is affected significantly by rainfall precipitation and increases by approximately 10–40% after rainfall events. The average degree of saturation in clayey embankment soil is the highest, as it is nearly twice that of silty embankment soil and triple that of sandy embankment soil. The depth of influence is greater when the fill material is finer and under dry subhumid climate conditions. The hydraulic responses are mainly influenced by evaporation under the weather conditions of Beijing, whereas they are more affected by precipitation under the weather conditions of Shanghai. The average degree of saturation in the sandy embankment soil under Shanghai weather conditions is greater than that in this soil under Beijing weather conditions. [ABSTRACT FROM AUTHOR]

Sanitary landfills and uncontrolled dumpsites are plastic wastes (PWs) reservoirs containing ∼60% of all the plastics ever made, amounting to 5,000 × 106 tons as of 2017. The distribution, long-term behavior, and release of macro- and microplastics (MPs) from disposal sites are critical to global plastics pollution, but are poorly understood and lack systematic assessments. We review comprehensively the available knowledge in the three aspects herein. The spatial and temporal distribution of PW in 616 municipal solid waste (MSW) samples retrieved from 275 disposal sites in 56 countries are summarized. The weight percentages of PW (%PW) generally decrease with increasing year of disposal and disposal depth. Other influential factors are disposal duration and country income level. The %PW values in different disposal sites show high regionality and spatial variability and heterogeneity. Disposal sites mostly have harsh temperature and stress, reactive liquids, and microbial activities, which are conducive to long-term processes of PW and MPs. The major processes are chemical degradation, dissolution, leaching and adsorption, biological degradation, mechanical wearing, pneumatic and hydrological transport and deposition, and conglomeration. PW leaves disposal sites via recycling, scavenging, mining, wind and surface runoff, coastal erosion and flooding, and slope failure. The release and removal pathways of PW from disposal sites have been recognized only qualitatively. In addition, the sources, presences, and secondary generation of MPs in disposal sites have been studied occasionally, whereas the transport and fate of MPs within and from disposal sites remain largely unstudied. [ABSTRACT FROM AUTHOR]

Affected by earthquakes and heavy rainfall, multiple landslide dams often cluster closely together along river reaches or gullies. Compared with a single landslide dam, the burst flood produced by the cascading failure of multiple landslide dams can be enhanced, seriously threatening life and property downstream. Here, we conduct a series of experiments in a 42 m flume to investigate the failure mechanisms of single and paired dams with fine-grained, well-graded, and coarse-grained debris; analyze the effects of dam geometry and initial water level of a downstream dam on the cascading breach; and quantitatively evaluate the amplification effect of cascading breach discharge. Single dams fail by overtopping along with seepage instability for a fine-grained dam, headcutting for a well-graded dam, and overtopping for a coarse-grained dam, respectively. The type of failure which occurs for a single dam is influenced by the shear strength of the dam material and seepage. However, the downstream dams in cascading tests fail by overtopping irrespective of dam material due to the large outburst floods from the upstream dams. A general flat slope angle is maintained during breaching for the fine-grained and coarse-grained dams, while a step-pool structure is developed for the well-graded dams because the finer grains are easier to wash away than coarse grains. The peak breach discharge for a downstream dam is 1.4–1.9 times the value for an upstream dam in the experimental runs, indicating the amplification effect of breach discharge. The amplification effect has a negative linear correlation with the time interval between the peak breach discharges of the two dams because the overlap of breach processes of upstream and downstream dams is gradually reduced as the time interval increases. [ABSTRACT FROM AUTHOR]

Debris flows are common geological hazards in mountainous regions worldwide. The scale of debris flows can be significantly enhanced by basal erosion and bank collapse in the transportation process, resulting in an increase in casualties and property losses. However, the mechanisms of this growth are largely unclear. Here, we conduct a series of experiments to investigate the erosion of two different bed sediments (coarse‐grained and widely graded) by released flows with three different densities and two different volumes. The erosion mechanisms of bed sediments are revealed by comparing detailed sensor data for flow level, pore pressure and total normal stress. A flow nose develops on the coarse‐grained bed sediment, resulting in a high flow depth and low velocity, while a tabular flow develops on the widely graded bed sediment, leading to a low flow depth and high velocity. The mean erosion rates of the coarse‐grained bed sediment are generally higher than those of the widely graded bed sediment due to significant pore pressure developed in coarse‐grained bed sediment. The feedback effect of bed sediment on the erosion process strongly influences the flow depth and velocity, which in turn affects the mean erosion rate of bed sediment. The interaction between the overlying flow and sediment bed controls the erosion pattern: coarse‐grained bed sediment is eroded by a layer of mass movement whereas widely graded bed sediment is progressively scoured. The interaction between debris flow and bed sediment during erosion is principally attributed to pore‐pressure transmission. Key Points: Flow depth and velocity over a coarse‐grained sediment (d50 = 2.4 mm) and a widely graded sediment (d50 = 0.9 mm) differed substantiallyThe coarse‐grained bed sediment was eroded by mass movement while the widely graded bed sediment was progressively scouredThe interaction between the overlying flow and sediment bed controlled the erosion pattern [ABSTRACT FROM AUTHOR]

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Summary: An analytical model for contaminant transport in multilayered capped contaminated sediments including the degradation of organic contaminant is presented. The effect of benthic boundary layer was treated as a Robin‐type boundary condition. The results of the proposed analytical model agree well with experimental data. The biodegradation of contaminant in bioturbation layer shows a significant influence on the flux at the surface of system. The maximum flux for the case with t1/2,bio = 0.07 year can be 4.5 times less than that of the case without considering the effect of biodegradation. The thickness of bioturbation layer has a significant effect on the performance of the capped contaminated sediment. The maximum flux for the case with lbio = 15 cm can be 17 times larger than that of the case without bioturbation layer. This may be because the effective diffusion coefficient of sand cap can be 28 times lower than Dbio. The mass transfer coefficient should be considered for the design of the capping system as the contaminant concentration at the top of system for the case with kbl = 2.5 × 10−5 cm/s can be 13 times greater than that of the case with kbl = 10−4 cm/s. The proposed analytical model can be used for verification of complicated numerical methods, evaluation of experimental data, and design of the capping contaminated sediment systems with reactive cap layers. [ABSTRACT FROM AUTHOR]

It is obvious that existence of hyperbolic eigenfunctions is dependent on HT ht . GLO:O8B/15dec20:nag3142-fig-0001.jpg PHOTO (COLOR): 1 Four types of eigenvectors and their correspondent eigenvalue range gl It is noted that the trigonometric-trigonometric (T-T) eigenvectors, the "regular" eigenvectors which always arise in eigenvalue problems and contribute to most of the terms in the infinite solution series,2 have already been studied and given in the original solution.1 The hyperbolic-hyperbolic (H-H), hyperbolic-trigonometric (H-T), and trigonometric-hyperbolic (T-H) eigenvectors, which were proposed by the discusser, were not considered in the original solution; and these eigenvectors only arise under some parameter conditions ( HT ht , Figure 1). [Extracted from the article]

At present, the dealkalization and comprehensive utilization of red mud is a worldwide problem. Studies on the settling performance and phase transformation of red mud by HCl, CaO, and HO leaching are limited. In this study, the characteristics of red mud were systematically analyzed. The average sizes of graded and initial red mud were 4.11 and 9.20 μm, respectively. X-ray diffraction (XRD), X-ray fluorescence spectra (XRF), and thermogravimetry-differential scanning calorimetry (TG-DSC) results indicated the different mineralogical phases, composition, and thermal behavior. The addition of HCl could neutralize the alkalization in the red mud slurry, and CaO could replace the Na and K. Notably, the pH of the red mud slurry had no obvious change with the increase in water washing times in a certain pH. Interestingly, soluble Al and Fe were not detected in the HCl-red mud and CaO-red mud. In addition, the settling ratio was used to express the settling performance of the red mud slurry. Their interaction mechanisms were proposed, which may include phase transformation and the changing of the size and surface area. The research provided a better understanding of the phase transformation and settling performance in the treatment of red mud by HCl, CaO, and HO leaching. [ABSTRACT FROM AUTHOR]

One-dimensional mathematical model is developed to investigate the behavior of contaminant transport in landfill composite liner system considering coupled effect of consolidation, diffusion, and degradation. The first- and second-type bottom boundary conditions are used to derive the steady-state and quasi-steady-state analytical solutions. The concentration profiles obtained by the proposed analytical solution are in good agreement with those obtained by the laboratory tests. The bottom concentration and flux of the soil liners can be greatly reduced when the degradation effect and porosity changing are considered. For the case under steady-state, the bottom flux and concentration for the case with t =10 years can be 2.8 and 5.5 times lower than those of the case with t =100 years, respectively. The bottom concentration and flux of the soil liners can be greatly reduced when the coefficient of volume compressibility decreases. For quasi-steady-state and with t = 10 years, the bottom flux and concentration for the case with m = 0.02/MPa can be 17.4 and 21 times lower than the case with m = 0.5/MPa. This may be due to the fact that the true fluid velocity induced by consolidation is greater for the case with high coefficient of volume compressibility. The bottom flux for the case with single compacted clay liner (CCL) can be 1.5 times larger than that for the case with GMB/CCL considering diffusion and consolidation for DCM. The proposed analytical model can be used for verification of more complicated numerical models and assessment of the coupled effect of diffusion, consolidation, and degradation on contaminant transport in landfill liner systems. [ABSTRACT FROM AUTHOR]

One-dimensional mathematical models for vapor-phase volatile organic compound (VOC) diffusion through composite cover barriers are presented. An analytical solution to the model was obtained by the method of separation of variables. The results obtained by the proposed solution agree well with those obtained by a numerical analysis. Based on the proposed analytical model, the VOC breakthrough curves of five different composite covers are compared. The effects of degree of saturation of geosynthetic clay liner (GCL) or compacted clay liner (CCL) on VOC migration in the composite covers are then presented. Results show that the composite cover barriers provide much better diffusion barriers for VOC than the single CCL. The top surface steady-state flux for a composite barrier, consisting of a 1.5 mm geomembrane (GM) and a 20 cm CCL, can be 8.3 times lower than that for a 30 cm CCL. The surface steady-state flux for the case with (1.5 mm GM + 6 mm GCL) was found to be 2.3 times lower than that for the case with (1.5 mm GM + 20 cm CCL). The degree of saturation Sr of the CCL has a great influence on VOC migration in composite covers when Sr is larger than 0.5. The steady-state flux at the surface of GM for the case with Sr = 0.7 can be 1.8 times lower than that for the case with Sr = 0.2. The proposed analytical model is relatively simple and can be used for verification of complicated numerical models, analysis of experimental data and performance assessment of composite cover barriers. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

One-dimensional mathematical models were developed for organic contaminant transport through landfill composite liners consisting of a geomembrane (GM) and a geosynthetic clay liner (GCL) or a GM and a compacted clay liner (CCL). The combined effect of leakage through GM defects, diffusion in GM and the underlying soil liners, and degradation in soil liners were considered. Steady state analytical solutions were provided for the proposed mathematical models, which consider the different combinations of advection, diffusion, and degradation. The analytical solutions of the time lag for contaminant transport in the composite liners were also derived. The performance of GM/GCL and GM/CCL was analyzed. For GM/GCL, the bottom flux can be reduced by a factor of 4 when the leachate head decreases from 10 to 0.3 m. The influence of degradation can be ignored for GM/GCL. For GM/CCL, when the leachate head decreases from 10 to 0.3 m, the bottom flux decreases by a factor of 2-4. Leachate head has greater influence on bottom flux in case of larger degradation rate (e.g., half-life = 1 year) compared to the case with lower degradation rate (e.g., half-life = 10 years). As contaminant half-life in soil liner decreases from 10 to 1 year, bottom flux decreases by approximately 2.7 magnitudes of orders. It is indicated that degradation may have greater influence on time lag of composite liner than leachate head. As leachate head increases from zero to 10 m, time lag for GM/CCL can be reduced by 5-6 years. Time lag for the same composite liner can be reduced by 10-11 years as contaminant half-life decreases from 10 to 1 year. Reducing leachate head acting on composite liners and increasing the degradation capacity of the soil liner would be the effective methods to improve the performance of the composite liners. The proposed analytical solutions are relatively simple and can be used for preliminary design and performance assessment of composite liners. [ABSTRACT FROM AUTHOR]

An analytical model for volatile organic compounds (VOCs) transport through a composite liner consisting of a geomembrane (GM), a geosynthetic clay liner (GCL), and a soil liner (SL) was developed for the assessment of the performance of this triple liner system. Both advection through the defects of GM and diffusion in the intact GM were considered in the model, and dimensionless analytical solution was obtained. The soil concentration profiles obtained by the proposed analytical solution have a good agreement with those obtained by the finite-layer-based software POLLUTE v7. The effects of leachate head, length of the connected wrinkles, and the interface transmissivity of GM/GCL on the breakthrough curves of the liner system were then investigated. Results show that the 30-year base flux of the liner system for the case with leachate head = 10 m and length of the connected wrinkles = 1,000 m can be over 60 times greater than that of the pure diffusion case. The length of the connected wrinkles of the GM has greater influence on the base flux of the liner system than on the base concentration. The interface transmissivity has negligible effect on the solute breakthrough curves of the liner system for relatively low values of the length of the connected wrinkles (e.g., <100 m). The groundwater protection level achieved by GM/CCL is more effective than that by GM/GCL/SL in the earlier times. However, the steady state base flux for GM/GCL/SL can be seven to eight times lower than that for GM/CCL. The analytical solution can also be used for experimental data fitting, verification of complicated numerical models, and preliminary design of composite liners. [ABSTRACT FROM AUTHOR]

The three-dimensional (3D) problem of the ground vibration isolation by an in-filled trench as a passive barrier is studied theoretically. Integral equations governing Rayleigh wave scattering are derived based on the Green’s solution of Lamb problem. The integral equations are solved accurately and efficiently with an iteration technique. They are used to evaluate the complicated Rayleigh wave field generated by irregular scatterers embedded in an elastic half-space solid. The passive isolation effectiveness of ground vibration by the in-filled trench for screening Rayleigh wave is further studied in detail. Effects of relevant parameters on the effectiveness of vibration isolation are investigated and presented. The results show that a trench filled with stiff backfill material gets a better isolation effect than a soft one, and increasing the depth or width of the in-filled trench also improves its screening effectiveness. The effectiveness and the area of the screened zone are surging with the increase in the length of the in-filled trench. [ABSTRACT FROM AUTHOR]

The transport process of nZnO in geosynthetic clay liner (GCL), an anti-seepage material used in municipal solid waste (MSW) landfills, under different seepage temperature conditions was conducted. The transport behavior of nZnO in GCL was analyzed. Results showed that the retardation performance of current GCL used in MSW landfills anti-seepage system against nZnO pollutants was poor. nZnO successfully permeated the GCL and entered external soil–groundwater environment, posing health threats to the life of organisms. Although seepage temperature exerted a small effect on nZnO suspension leakage volume, change in seepage temperature affects the mass of transported nZnO in GCL by redispersion of nZnO in suspension. As the seepage temperature increases, the mass of nZnO that permeated the GCL increases, reaching a maximum at 50 °C, and then decreases. [ABSTRACT FROM AUTHOR]