A comprehensive series of tests, including dynamic triaxial, monotonic triaxial and unconfined compressive strength (UCS) tests, were carried out on reconstituted landfill waste material buried for over twenty years in a closed landfill site in Sydney, Australia. Waste materials collected from the landfill site were treated with varying percentages of cement, and both treated and untreated specimens were investigated to evaluate the influence of cement treatment. The study examined the dynamic properties of cement-treated landfill waste, including cumulative plastic deformation, resilient modulus, and damping ratio, and also analysed the impact of cyclic loading on post-cyclic shear strength in comparison to pre-cyclic shear strength. The UCS tests and monotonic triaxial tests demonstrated that untreated specimens subjected to monotonic loading exhibited a progressive increase in strength with rising axial strain, whereas cement-treated specimens reached a peak strength before experiencing a decline. During cyclic loading, with the inclusion of cement, a significant reduction in cumulative plastic deformation and damping ratio was observed, and this reduction was further enhanced with increasing cement content. Conversely, the resilient modulus showed substantial improvement with the addition of cement, and this enhancement was further amplified with increasing cement content. The formation of cementation bonds between particles curtails particle movement within the landfill waste material matrix and prevents interparticle sliding during cyclic loading, leading to lower plastic strains and damping ratio while increasing resilient modulus. Post-cyclic monotonic testing revealed that cyclic loading caused the partial breakage of the cementation bonds, resulting in reduced shear strength. This reduction was higher on samples treated with lower cement content. Overall, the findings of the research offer crucial insights into the possibility of cement-treated landfill waste as a railway subgrade, laying the groundwork for informed design decisions in developing transport infrastructure over closed landfill sites while using landfill waste materials available on site.

The remediation and management of old municipal solid waste (MSW) landfills are pivotal for advancing urban ecological sustainability. This study aims to systematically assess the mechanical properties, environmental behaviors, and synergistic mechanisms of remediated landfill-mined soil-like material (SLM) through advanced oxidation and stabilization processes. The results indicate that synergistic remediation with advanced oxidation and stabilization processes significantly increased the mechanical strength of stabilized SLM to over 0.6 MPa, and reduced the organic content by about 20 %, making it suitable for reuse in geotechnical engineering. The choice of oxidizing agents markedly affected the mechanical properties of stabilized SLM; for example, the application of sodium percarbonate in conjunction with stabilized materials further enhances the strength by simultaneously promoting the pozzolanic reaction. Furthermore, the heavy metal leaching behaviors of the stabilized SLM were found to be environmentally safe. The enhanced performance of stabilized SLM is primarily attributed to the synergistic effects of oxidation and pozzolanic reactions. The advanced oxidation process decreases organic matter content and increases its stability by reducing the proportion of readily decomposable O-alkyl C. Concurrently, pozzolanic reactions produce ettringite crystals and C-(A)-S-H gels, which not only fill micropores and improve particle bonding but also aid in heavy metal immobilization through surface adsorption, complexation, and physical encapsulation. These insights provide a comprehensive understanding of the remediation processes and resource recovery potential of SLM from old MSW landfills.

One of the fundamental challenges in municipal waste management is ensuring the long-term stability of landfills. Slope instability in these structures can lead to irreparable consequences, including environmental pollution, infrastructure destruction, and public health threats. Therefore, accurate assessment and prediction of slope behavior in these structures is of particular importance. In this study, a new method based on fuzzy logic has been proposed to assess and predict slope stability in landfills. Fuzzy logic, as a powerful tool in modeling complex and uncertain systems, allows for more accurate analysis of landfill behavior. In order to conduct the present study, various steps were taken, including data collection, modeling with fuzzy logic, determining model coefficients, and model validation. In the first step, field data were collected from various excavations such as slope geometry, soil mechanical properties, groundwater level, loading due to waste, etc. Then, a fuzzy logic model was developed to analyze slope stability. In this model, input parameters such as slope, elevation, soil type, and groundwater level were described as linguistic variables and converted into fuzzy numbers using membership functions, and finally, fuzzy rules were defined to express the relationships between inputs and output (slope stability or instability). In the next step, field and laboratory data were used to determine the coefficients of the fuzzy model, and using optimization methods, the model parameters were adjusted in such a way that the model output was consistent with the observed data. In the last step, the developed model was validated using new data. For this purpose, the model results were compared with the observed data and the accuracy and reliability of the model were evaluated. The results show that the developed model will be able to predict the probability of slope instability with high accuracy and identify areas with high risk of instability in landfills. Also, it was determined that by analyzing the sensitivity of the model, important factors that affect slope stability can be identified. According to the model results, appropriate solutions can be provided to improve slope stability, such as changing the slope angle, soil reinforcement, and drainage. As a general conclusion, based on the observations of the present study, it can be said that using fuzzy logic in analyzing the slope stability of landfills is a new and efficient approach that can significantly contribute to improving urban waste management and reducing risks from slope instability.

It is a fact that the temperature inside the waste mass is higher than the ambient outside the landfill. However, only a few experimental works have tried to address the effect of such elevated temperatures on the mechanical behavior of waste. Accordingly, developing a constitutive model based on experimental achievement is still incipient. In this paper, results from experimental literature and the results of a complementary testing campaign aided in better understanding and modeling the waste thermo-mechanical behavior. An existing model framework by the authors is extended to incorporate thermal effects on the waste bulk and fibrous reinforcement particles. The model predicted fairly the mechanical behavior of waste in terms of deviatoric stress, pore water pressure, and volumetric strains in drained and undrained triaxial tests performed on samples at different temperatures and with different plastic contents. Values of deviatoric stress predicted by the model for two specific axial strains are compared with experimental results, considering all the tested samples, proving the model's capabilities in reproducing the waste's overall behavior. Considering an axial strain of 20%, the probabilities of the model error occurrence in the range of +/- 25% are 55% and 67% for CIU and CID tests, respectively.

Biochar, as an environment-friendly soil amendment, has been extensively proposed in landfill cover, primarily for promoting soil hydraulic properties, such as hydraulic conductivity and soil water retention. However, the impact of biochar derived from various feedstocks on soil-biochar mix properties, particularly gas permeability under unsaturated conditions, remains under-explored. This study evaluates how different types of biochar influence gas permeability and soil water retention. Five biochars pyrolyzed using different biomass waste, such as apple wood, reed straw, walnut, corn cob and corn straw, were each mixed with sandy soil in a 5% mass ratio. Gas permeability and hydrological response (water content, matric suction) were measured during wet-dry cycles. Results indicated that biochar amendments generally enhanced water retention compared to bare soil. Apple wood biochar, in particular, significantly improved both water content (reaching 90% of the control's maximum moisture content) and suction (peaking at 2755 kPa), outperforming reed straw, walnut, corn cob and corn straw biochars. This enhancement stems from apple wood biochar's hydrophilic functional groups (e.g., -OH), which improve soil hydrophilicity and water-biochar interactions. Its large specific surface area and tightly arranged micropores further enhance suction. Gas permeability rose with increasing suction, with reed straw and apple wood biochars increasing gas permeability by 196% due to their larger average pore sizes and the formation of more meso-macro pore structures in the sandy soil. Conversely, walnut and corn cob biochars reduced soil permeability, suggesting their suitability for high-pressure applications. These findings guide the use of biochar-amended soil in landfill covers to mitigate gas emissions.

Lysimeters are frequently employed to replicate environmental conditions in landfill scenarios due to their relatively economical nature and brief study duration. Lysimeters frequently exhibit varying geometrical characteristics that modify the physical and thermodynamic attributes, potentially influencing waste material's decomposition rate and leaching dynamics. Based on the results of the lysimeter tests, lysimeters effectively evaluate and predict the impact of magnesium oxide (Mgo), a material suitable for constructing landfill liners. The findings substantiate that lysimeter investigations can significantly contribute to landfill engineering by identifying optimal strategies for waste containment and selecting appropriate materials for fabricating landfill barriers. Throughout the experimental procedure, the lysimeter was subjected to leachate application. In each hour of the experiment, the quantities of moisture, electric conductivity value (EC), temperature, settlement, pressure reaching the liner, and the total volume and pH of the obtained effluents were measured each week. This research explores and analyzes the role of magnesium oxide (C-M) in reducing permeability and measuring the shear strength properties of the composite material by utilizing a triaxial test. The sensor results demonstrated that MgO-enhanced liners provided superior long-term performance compared to clay. EC sensors showed MgO liners had lower and more stable conductivity. Moisture content sensors indicated that MgO-treated soil maintained better moisture regulation, reducing leachate. LVDT sensors revealed that MgO liners had minimal settlement, while clay experienced greater and prolonged settlement. Temperature sensors confirmed MgO's consistent thermal stability. In contrast, pressure, Total Dissolved Solid (TDS), pH, and flow rate sensors highlighted MgO's better structural integrity, lower dissolved solids, and controlled permeability over time.

Featured Application The findings of this study establish the behavior of sanitary landfill cover materials, such as compacted clay and compacted polyurethane-clay, in unsaturated conditions under several wet-dry cycles, which would aid in predicting the performance of the material under varying environmental conditions. By predicting the unsaturated hydraulic conductivity and understanding the effects of environmental stresses, the findings can aid in the design and implementation of more durable and efficient landfill liners and covers.Abstract Sanitary landfill covers are exposed to varying environmental conditions; hence, the state of the clay layer also changes from saturated to unsaturated. The study aimed to predict the unsaturated hydraulic conductivity of the locally available compacted clay and clay with polyurethane to determine their behavior as they change from wet to dry using matric suction and empirical models proposed through other studies. The specimens underwent three wet-dry cycles wherein the matric suction was determined for several moisture content levels as the specimen dried using the filter paper method or ASTM D5298. The results showed that the factors affecting the soil structure, such as grain size difference between clay and polyurethane-clay, varying initial void ratios, and degradation of the soil structure due to the wet-dry cycles, did not affect the matric suction at the higher suction range; however, these factors had an effect at the lower suction range. The matric suction obtained was then used to establish the best fit water retention curve (WRC) or the relationship between the matric suction and moisture content. The WRC was used to predict the unsaturated hydraulic conductivity and observe the soil-water interaction. The study also observed that the predicted unsaturated hydraulic conductivity decreases as the compacted specimen moves to a drier state.

Loose fill slopes are prevalent worldwide, and their failure during rainstorms is frequently documented. While existing studies have primarily focused on the initiation of such failures, the post-failure motion of rainfallinduced loose fill slope failures has rarely been explored. This study addresses this knowledge gap by investigating both the initiation and subsequent motion of rainfall-induced loose fill slope failures. To achieve this goal, a hydro-mechanical coupled MPM model was utilized to back-analyze the catastrophic 1976 Sau Mau Ping landslide in Hong Kong and conduct parametric studies. From an engineering perspective, the contractive behaviour of loose coarse-grained soil, which induces positive excess pore water pressure and leads to Bishop's stress reduction and a drop in strength, is a major factor contributing to this landslide. The entire failure process can be classified into three phases with different failure modes: local slide, global slide, and flow-like slide, closely related to the soil stress path. The computed results closely match the field measurements on various aspects, including the landslide zone, mobilized volume, and runout distance. The parametric studies reveal that the landslide zone, mobilized soil volume, and final runout distance decrease with a lower value of dilation angle and a smaller critical state plastic deviatoric strain. Conversely, in the case of a constant SWRC, there tends to be an overestimation of these parameters. It is therefore important to consider soil contraction and its influence on hydro-mechanical behaviour.

The research assesses the environmental impacts of waste management in Fez, Morocco, in line with the legal standards set by law 28-00 on waste management and law 12-03 on environmental impact assessment. Using the DPSIR framework (Drivers, Pressures, State, Impact, Response), 43 unregulated landfills were analyzed to assess their impacts on water, air, soil, biodiversity, and socio-economic activities. The results reveal medium to major impacts, predominantly local but continuous, affecting soil, water, air, and ecosystems. Human-related impacts include noise pollution and health risks, though there are also positive effects, such as job creation. While drought has lessened some water-related impacts, the overall disruption to ecosystems and communities is significant. The key message of this investigation is that unregulated waste management in Fez is causing ongoing environmental damage, particularly through illegal landfills. This research underscores the necessity of improving waste management strategies by integrating systematic evaluation methods like DPSIR. By providing a more systematic approach to understanding the complex interactions between waste and the environment, these findings are essential for shaping future waste management policies and promoting better environmental integration in urban planning.

This study investigates the long-term effects of landfill leachate contamination on soil hydraulic conductivity and shear strength parameters over a 12-month period, addressing the current lack of comprehensive long-term experimental data in this field. Laboratory permeability tests and direct shear tests were performed on sandy clayey silt samples contaminated with leachate at concentrations ranging from 5% to 25%. Microstructural and mineralogical analyses were conducted using SEM and XRD to identify the mechanisms behind observed changes. The results identify a critical threshold at 15% contamination where soil behavior transitions from granular to cohesive characteristics, marked by significant changes in both hydraulic and mechanical properties. Hydraulic conductivity increases at low contamination levels but decreases significantly at higher levels, while friction angle shows an immediate reduction from 36.5 degrees to 31-31.5 degrees and cohesion exhibits a three-phase evolution pattern, reaching peak increases of 151.5% at 15% contamination. The hydraulic conductivity changes are controlled by contamination level rather than exposure time, maintaining stable values throughout the testing period, whereas shear strength parameters demonstrate more complex temporal evolution patterns. These findings provide essential parameters for landfill design and stability assessment, demonstrating how leachate concentration affects long-term soil behavior through mineral formation and structural modification.