The main objectives of this study were to identify methane hotspots through spatial distribution tests of the surface methane concentration above a landfill final cover and to investigate the effects of rainfall, atmospheric pressure, ground temperature, and ambient methane concentration on methane emissions. A portable laser methane detector was used to measure the spatial distribution of methane concentrations. The methane concentration distribution showed a distinct spatial variability. The maximum methane concentration reached 3225 ppm, while 73.0% of the methane concentration values were below 10.0 ppm. Several meteorological factors were found to be associated with the variation in methane emissions. Rainfall limited gas transport in the cover, resulting in more significant methane hotspots. Atmospheric pressure was negatively correlated with methane emission. The ambient methane concentration and methane flux had a significant positive linear correlation. Based on a linear correlation equation, the spatial distribution of methane concentrations in the landfill could be converted into a methane emission distribution. The estimated average value for methane emissions in the test area was approximately 4.3 g m⁻² d⁻¹. This study provides an experimental basis for locating methane hotspots and assessing methane emissions in landfill final covers, and proposes supplementary means for detecting geomembrane damage in landfill covers.

Bentonite was modified with cetyltrimethylammonium bromide (CTAB). The organically modified bentonite (OMB) was used to remove phenol from aqueous solution, the microstructural changes were characterized by X-ray diffraction (XRD) and scanning electronic microscopy (SEM), and phenol adsorption kinetic was obtained using batch adsorption test results. The results indicated that the rate of adsorption of phenol onto the OMB was positively correlated with the initial concentration, and the maximum adsorption capacity was found to be 10.1 mg/g at the initial concentration of 150 mg/L at 25 °C and pH 10. The investigations of adsorption kinetics models showed that the adsorption kinetic was better reflected by the pseudo-second-order kinetic model. Furthermore, the properties of the OMB samples with different adsorption times were obtained by SEM and XRD. The statistic analysis revealed that the pore diameter of the OMB samples decreased with the increasing adsorption time and gradually reached equilibrium.

A novel technique that couples microbially induced calcite precipitation (MICP) and calcium carbide residue (CCR) is proposed for immobilizing Cd²⁺ in contaminated soil. The properties and mechanism of CCR-enhanced MICP were investigated through a series of experimental analyses considering factors such as heavy metal concentration, curing time, and the effect of Ca²⁺. The unconfined compressive strength (UCS) increased with increasing curing time and reached a maximum value at 28 d, and the leaching concentration of Cd²⁺ decreased and tended to level off with increasing curing time. The addition of CCR enhanced the immobilization performance of Cd²⁺ through the MICP method, resulting in UCSs that were 3.8–4.2 times those of samples without CCR and leaching concentrations of Cd²⁺ that were 38.9–69.2% lower at a curing time of 28 d. The addition of Ca²⁺ to cementation solutions further improved the immobilization effectiveness, resulting in the UCSs of the samples increasing by 18.7–49.8% and the leaching concentrations of Cd²⁺ decreasing by 11–40% CaCO₃ and its hydration products can immobilize Cd²⁺ through coprecipitation, reducing its toxicity by converting weak acid-extractable cadmium into residual cadmium. Consequently, Sporosarcina pasteurii combined with CCR improved the UCS of the treated contaminated soil and greatly decreased cadmium migration.

Embankment with pile-supported foundation (PSF) is widely used for high-speed railway (HSR) built in soft ground. Although extensive studies have been conducted on the effectiveness of PSF in reducing ground vibration via numerical analyses, the soil–water coupling in soft ground and response discrepancies among different types of PSF are seldom considered. In this study, 2D elastoplastic FEM was conducted to verify the necessity of soil–water coupling analysis and clarify the response discrepancies among different types of PSF, such as pile-net foundation, pile-raft foundation and pile-plate foundation. Numerical results indicate that liquid phase in soft ground plays an important influence on the dynamic response of HSR, the vertical acceleration and displacement will be overestimated while EPWP will be underestimated if soil–water coupling is not considered. Besides, single-phase analysis exaggerates the acceleration attenuation and underestimates the vibration amplification in soft ground. PSF induces significant stress fluctuation in the embankment and stronger vibration beneath the pile end compared to the unreinforced ground, moreover, the distributions of vertical acceleration and EPWP from PSF are partitioned sharply by the piles while vertical dynamic displacement becomes more uniform within the pile reinforced area. The peak acceleration and EPWP in soft ground are significantly different among different types of PSF, overall, the larger stiffness of PSF is, the smaller the peak acceleration and EPWP may be. However, the peak displacements are similar in different cases for the dynamic displacement is basically controlled by the piles rather than the slab or pile cap. The present research gives an insight to analyze high-speed train induced EPWP and settlement accumulation in soft ground.

The high-temperature and high-humidity conditions arising from the biochemical degradation of landfill waste result in significant temperature gradients within the landfill cover. The effects of waste temperature on landfill gas transport and microbial aerobic methane oxidation are not fully understood. In this study, a fully coupled theoretical model was developed to simulate the interactions of moisture, heat, and gas transport within a capillary barrier cover. A series of parametric studies were carried out to investigate the influence of the combined effects of temperature gradient, initial soil moisture content, and landfill gas generation rate on methane transport, oxidation, and emissions. The simulated results indicated that increasing waste temperature intensified the temperature gradient, leading to higher surface evaporation rates and variations in methane oxidation efficiencies. Additionally, variations in initial soil moisture content and landfill gas generation rates were found to significantly impact gas migration and methane oxidation in the cover. This study demonstrates the critical role of waste temperature in landfill gas migration within landfill cover systems, providing technical methodologies for the optimized design of soil cover systems.