The characteristics of landfilled municipal solid waste have great influence on the design, operation, and management of landfills, affecting settlement, slope stability, and leachate/gas well integrity. Through analysis and study we observed that the landfill method is widely used to dispose of municipal solid waste (MSW), especially in developing countries. The research results of MSW landfill properties are different due to waste inhomogeneity. In this paper, MSW physical composition, unit weight, and permeability coefficient of landfills in several countries were reviewed and discussed. Landfilled MSW has strong regional and temporal characteristics. Landfilled MSW of developing countries has high organic content ranges from 75.00% to 97.15%. The organic contents in landfills of most developed regions are relatively small. The unit weight ranged from 4.9-17.8 kN/m³ and the permeability coefficient ranged from 3.5×10^-2 cm/sec to 5.0×10^-8 cm/sec within 60 m. In the process of waste degradation, MSW physical composition, unit weight, and permeability coefficient are changed. Waste classification improves the recovery and utilization of landfill and reduces the amount of waste, which affects the characteristics of landfilled MSW. Thus, strengthening waste classification, recycling, and recovery of MSW is significant and meaningful for construction, operation, and management of landfills.

With the rapid increase of city waste, landfills have become a major method to deals with municipal solid waste. Thus, the safety of landfills has become a valuable research topic. In this paper, Jiangcungou Landfill, located in Shaanxi, China, was investigated and its slope stability was analyzed. Laboratory tests were used to obtain permeability coefficients of municipal solid waste. Based on the results, the distribution of leachate and stability in the landfill was computed and analyzed. These results showed: the range of permeability coefficient was from 1.0 × 10^–7 cm sec^–1 to 6.0 × 10^–3 cm sec^–1 on basis of laboratory test and some parameters of similar landfills. Owing to the existence of intermediate cover layers in the landfill, the perched water level appeared in the landfill with heavy rain. Moreover, the waste was filled with leachate in the top layer, and the range of leachate level was from 2 m to 5 m in depth under the waste surface in other layers. The closer it gets to the surface of landfill, the higher the perched water level of leachate. It is indicated that the minimum safety factors were 1.516 and 0.958 for winter and summer, respectively. Additionally, the slope failure may occur in summer. Implications: The research of seepage and stability in landfills may provide a less costly way to reduce accidents. Landslides often occur in the Jiangcungou Landfill because of the high leachate level. Some measures should be implemented to reduce the leachate level. This paper investigated seepage and slope stability of landfills by numerical methods. These results may provide the basis for increasing stability of landfills.

Landfilled municipal solid waste has evident heterogeneity, and clogging of the drainage layer can easily happen during operation of the landfill. These two factors significantly influence the distribution of leachate in a landfill. Herein, the distribution of waste permeability in the spatial and temporal domains was analyzed. Then, changes to the drainage‐layer permeability in the temporal domain were fitted to these data. A simple model of multilayer waste slope was established combining the finite element software and a user subroutine. Herewith, changes of permeability in the waste and drainage layers were simulated, such that the heterogeneity of waste and the process of clogging of the drainage layer could be simulated. Then, the leachate distributions and transport conditions of nine schemes for landfill were analyzed. The results indicated that the distribution curve of waste‐saturated permeability follows a logarithmic relation in the vertical direction, and the distribution curve of fresh‐waste‐saturated permeability follows a polynomial relation in time. After each landfill is worked for a few years, the drainage layer always encounters clogging problems of some kind and its permeability decreases by one to five orders of magnitude. Through numerical models, the simulation results of the permeability distribution in the spatial and temporal domains were found satisfactory. When the permeability distributions were layered in the buried depth, pore pressures and leachate levels are smaller than the logarithmic distributions. During the process of degradation, the pore pressures and leachate levels are increased slightly under the consideration of the polynomial distribution of waste permeability in time. With clogging of the permeability of the drainage layer, the pore pressures and leachate levels of landfill were found to be increasing gradually. To obtain results closer to that of actual situations, corresponding models should be established and analyzed based on a range of permeability, waste degradation rate, and degree of clogging.

High leachate levels seriously affect slope stability in landfills. Heavy rainfall and degradation of waste are the main causes of high leachate levels. Here, we analyze rainfall patterns, simulate leachate levels, and suggest methods for reducing the impact of heavy rain on slope stability. Heterogeneous characteristics of waste piles are simulated by combining a user subroutine with the finite element method. Finally, under maximum daily rainfall conditions at the landfill, seepage is simulated in three dimensions. We find that heterogeneities in hydraulic conductivity are often responsible for perched leachate levels. For a given rainfall, the leachates are perched in multiple places with the least rainfall duration; for a given rainfall duration, the leachates are perched in multiple places with the greatest rainfall intensity. High leachate levels exist downstream of the landfill slope and they dissipate slowly. From the initial rainfall to 2.8 hours after the rain, more saturated zones exist in the simulated landfill, especially near landfill slopes. In order to stabilize landfills for safety, we suggest the use of drainage measures, including silo systems, at the top of the waste pile and near slopes in order to reduce leachate levels.

Ventilation problems are critical in tunnel engineering, and the loss of air volume in ventilation ducts is generally estimated using empirical methods. The air volume calculation makes it difficult to meet the accuracy requirements, resulting in resource waste or insufficient air supply. In this study, the forced ventilation system of the tunnel under construction was investigated based on the computational fluid dynamics method. The mechanism of air leakage on airflow distribution and pollutant transport in the tunnel is determined. Air leakage reduces the distribution peak of pollutants and effectively accelerates the emission of harmful gases. However, this effect decreases with distance from the air duct inlet. Through the calculation results of nearly one hundred models, it is found that the air leakage of the duct can be fitted by logarithmic function and verified by empirical equation. The matching degree between the fitting function of the model and the empirical equation depends on the length of the tunnel. On this basis, the calculation formula of effective air volume near the working face is derived. This study can be applied to the ventilation engineering of the tunnel under construction and provide a theoretical basis for the calculation of the effective air supply.

The distribution of leachate directly impacts the safety and stability of the landfill, so it is important to research the distribution of seepage characteristics and migration patterns of leachate. The study aims to investigate the impact of heterogeneous permeability distribution and clogging of the drainage layer on leachate transportation in landfills. To achieve this, a heterogeneous transient seepage model was developed. Results showed that when considering the heterogeneous permeability of the waste in the buried depth direction, the maximum perched water level was higher, which is not conducive to the safety and stability of the landfill. Taking Xi’an Jiangcungou Landfill as a research object, the maximum perched water level of each waste layer was higher compared to the homogeneous condition when considering the landfill process and heterogeneous permeability. The differential value ranged from 0.08 m to 1.88 m. Furthermore, the calculation results obtained from the heterogeneous seepage model were found to be in good agreement with both actual field data and referenced survey data, thus confirming the reliability of the model. These research findings not only offer technical support but also provide a solid theoretical foundation for leachate level control and safety and stability assessments.