Yijun Chen

Experimental research on the evolution laws of soil fabric of compacted clay liner in a landfill final cover under the dry–wet cycle

AbstractThis paper aims to investigate the structural damage in compacted clay liner (CCL) caused by the dry–wet cycles in a landfill final cover. Experimental research is performed on the microstructure evolution of CCL under repeated dry–wet cycles and different initial compactness (90, 94, and 98xa0%). Results show that the pore size distribution of CCL has multifractal characteristics which can be classified into five self-similar intervals: macropore (>15xa0μm), medium-pore (8–15xa0μm), small-pore (0.3–8xa0μm), mesopore (0.04–0.3xa0μm), and micropore (<0.04xa0μm). The compression proportion of the different intervals is not equal and constant with the increase in compactness. Maximum compression interval is observed among small-pores and mesopores, with compactness ranging from 90 to 94xa0% and from 94 to 98xa0%, respectively. The effect of the dry–wet cycles mainly focuses on small-pores, medium-pores and macropores, while having little effect on meso-pores and micro-pores. The increase of macropores is one of the reasons for increase in the permeability of CCL, but it is not the main reason. Cracks causing by the irreversible shrinkage of pores is the main reason leading to permeability with an orders of magnitude increment, and improving the compactness can reduce the structural damage of CCL under the function of dry–wet cycles.nRésuméCet article vise à étudier l’endommagement structurel de la couche dargile compactée (CAC) causée par les cycles de séchage-saturation dans une couverture finale de la décharge. L’étude expérimentale est effectuée sur lévolution de la microstructure du CAC sous cycles répétés de séchage-saturation et différents compacité initiale (90, 94, and 98%). Les résultats montrent que la distribution de taille de pore de CAC a des caractéristiques multifractales qui peuvent être classés en cinq intervalles auto-similaires: macropores (>15 μm), pores moyens (8 - 15 μm), petits pores (0,3- 8 μm), mésopores (0,04- 0,3 um), et des micropores (<0,04 μm). Les proportions de compression des différents intervalles ne sont pas pareilles et constant avec laugmentation de la compacité. L’intervalle de compression maximale est observée dans les petits-pores et les mésopores, avec une compacité comprise entre 90% et 94% et de 94% à 98%, respectivement. Leffet des cycles de séchage-saturation se concentre principalement sur les petits pores, pores moyens et les macropores, alors que peu deffet sur mésopores et micropores. Laugmentation de macropores est lune des raisons qui augmentent la perméabilité du CAC, mais ce nest pas la raison principale. La fissuration due au retrait irréversible des pores est la raison principale qui mène à des ordres de grandeur en augmentation de perméabilité, et lamélioration de la compacité peuvent réduire l’endommagement structurel du CAC dans la fonction de cycles séchage-saturation.

Coupling effect of landfill leachate and temperature on the microstructure of stabilized clay

This paper studies the microstructure of stabilized clay polluted by landfill leachate at different temperatures. For this purpose, dynamic corrosion-stabilized clay was used to prepare mercury intrusion porosimetry and scanning electron microscopy samples by lyophilization. The results showed that a rise in temperature affects the pore structure of corrosion-stabilized clay. Macropores are easily produced when the temperature ranges from 40 to 60xa0°C, while cryptopores and ultramicropores appear in significant numbers if the temperature reaches 80xa0°C. The corresponding micrographs show a dispersed structure at temperatures of 40 to 60xa0°C and a clearly flower-like structure at 80xa0°C. Landfill leachate has obvious effects on the microstructure of stabilized clay. After corrosion processes, pore size is reduced while average pore radius is increased. Macropores increase and span a wider range. The peak of the pore size distribution curve shifts from the middle to both ends; porosity initially decreases and then increases. From the chemical point of view, this corrosion mechanism is mainly due to the growth of new material such as calcium chloro-aluminates, ettringite or dihydrate gypsum that were generated by the reaction between landfill leachate and stabilized clay.

Erosion characteristics of ecological sludge evapotranspiration cover slopes for landfill closure

The runoff and sediment processes under different conditions are investigated by the laboratory tests performed in ecological sludge evapotranspiration cover slopes of landfill closure. Erosion caused by rainfall is investigated in the bare slope and vegetation litter layer. Erosion easily occurs when the condition of the bare slope reaches 100xa0% coverage. The different matrices for sediment control are crucial for the specific condition. The ecological sludge evapotranspiration technology (EST) composite matrix has been prepared by modified sludge added with fiber and a piece of net. Under the condition of 30° slope and 80xa0mm/h rainfall intensity, modified sludge and clay have a similar basic runoff tendency. The modifier sludge naked slope reduces approximately 20xa0% the sediment value compared with that of clay naked slope. The EST composite matrix could provide the smallest sediment value in both non-vegetation and vegetation conditions. Vegetation in the modified sludge has a significantly faster growth than that for the cases of clay. The results show that EST composite matrix with grass used as the vegetation layer of the landfill cover system is very important and obviously feasible.

Investigation of a fluid–solid coupling model for a tailings dam with infiltration of suspended particles

The study of the migration and deposition characteristics of suspended particles in porous media is significant in petroleum exploitation, groundwater recharge, filter design, nuclear waste disposal, and migration of underground pollutants. In recent years, researchers have tended to neglect the influence of tailings particle movement on seepage action in stability analysis of tailings dams. They have focused on analyzing the influence of tailings particle movement and deposition on tailings dams’ physical parameters. Based on the effective stress principle, the suspended-particle deposition equation is incorporated into the model of the fluid–solid coupling seepage field and combined with the stress field equation. Then, the particle deposition fluid–solid coupling model is established and gives the proper solution conditions for simplification. Based on a calculation program developed in-house, the stability of a tailings dam is analyzed while taking into account suspended particles. This approach aims to gradually reduce variation in percolation time growth of the coefficients of permeability and porosity. On this basis, we monitor the horizontal displacement and sedimentation values of the primary dam crest and of all levels of the sub-dam. We explore preliminarily the distribution law for tailings pore pressure to validate the correctness of the proposed mathematical model. Numerical analysis results show that in the process of deposition, the porosity, permeability coefficient, and flow rate become progressively smaller. The displacement of the primary dam is minimal and displacement of the third sub-dam is the largest, with displacement size displaying a relationship with dam height. The vertical displacement of the dam top gradually increases with increasing grades of sub-dams, and the difference is nearly 0.5xa0cm between the displacement of the primary and third dam crest-monitoring points. The results provide a theoretical basis for stability analysis of tailings dams undergoing tailings particle infiltration. Moreover, they provide reference material for studying migration and deposition characteristics of suspended particles in porous media.

Dynamic characteristics of tailings reservoir under seismic load

Earthquake is one of the most important factors that leads to the liquefaction of tailings and to the instability of the tailings reservoir. Therefore, it is of great practical significance to study the instability mechanism of the tailings reservoir under seismic load. In this study, the dynamic characteristics of the tailings reservoir under seismic load were investigated by carrying out a model test on the dynamic characteristics of the tailings dam. A model test of tailings dam failure and the dynamic characteristics model of the tailings reservoir under seismic load were established. Additionally, the dynamic characteristics under a seismic load were investigated. Additionally, the correctness of the dynamic characteristics model of the tailings reservoir was verified by numerical calculation. Researches show that with the increase in input peak acceleration, pore water pressure, earth pressure, and the horizontal and vertical displacements of the dam monitoring points are gradually increased. However, the acceleration amplification factor shows a declining trend. In the process of increasing the input peak acceleration, the saturation line and the lifting speed increases gradually. There is no obvious slip surface in the failure of the tailings dam, and the overall sliding is shown by the failure mode. The tailings reach each of the downstream sections. The mud height increases to the peak value, and then decreases gradually until stagnation. The results of this study can provide the theoretical basis and reference values for the stability analysis of a tailings reservoir under a seismic load, and the results are of great significance for controlling the risk factors in the operation of tailings reservoir, reducing the risk of tailings production safety, preventing the occurrence of tailing pond accidents, protecting the property safety of the downstream residents and enterprises, maintaining social stability around the reservoir area and creating a good ecological environment.