Methane emissions through landfill cover is a complicated multi-physics coupled process, including water-gas-heat transfer and microbial aerobic methane oxidation (MAMO). Due to the relatively high water content of municipal wastes in China, landfill gas generally contains a substantial amount of water vapor. Moreover, the biochemical decomposition of wastes underneath landfill cover results in noticeable temperature gradient across the cover. Nevertheless, effects of water vapor and temperature gradient on water and gas distributions in landfill cover are not clear. A new theoretical model of water-gas-heat reactive transfer and MAMO in unsaturated soils was developed by incorporating vapor flow and effects of temperature gradient on water and gas transfer. The newly proposed model was implemented in a finite-element software COMSOL. The model was verified by (i) a published soil column test simulating MAMO; and (ii) a soil column test subject to heating. The model is capable of describing liquid water-vapor transfer, multi-component gas transfer (e.g., CH4, CO2, N2 and O2), heat transfer and MAMO. The theoretical model and the related numerical code could serve as a useful tool for landfill cover design for mitigating methane emissions.

We propose a novel approach to capture the hysteresis of suction–degree of saturation (s–S), relationship of three–phase fluids in porous media. We defined effective suction, s', that incorporates the delay in the variation of saturation due to hysteresis, with its movement in a closed domain in suction space. This domain defines a possible range of effective suction in which matric suction s always locates at the center of locus, and the incremental change in matric suction determines the movement in the effective suction space. This effective suction is incorporated in a unique s–S relationship defined by the van Genuchten’s equation to obtain a delayed variation in the degrees of saturation caused due to hysteresis during wetting and drying scanning paths. Through the incorporation of entire effective suction space in the van Genuchten’s s–S relationship, we proposed a direct and modest approach to represent the saturation of air, NAPL, and water through a single point in a triangular model along with their possible respective hysteretic variation in both, 2–phase and 3–phase systems. Vertical profiles of realistic soil behavior are also simulated to understand the effect of hysteresis by incorporating the proposed model in a 3–phase system.

In embankment dams and hydraulic structures, locally excavated sandy gravel is extensively used as the major rockfill material for its relatively low cost. As an increasing number of hydraulic buildings are designed with higher height and are constructed at steep valleys as well as turbulent waterways, the hydraulic conductivity performance of this building material becomes a vital parameter to evaluate the structure safety against seepage. This paper focuses on the changes of hydraulic conductivity induced by coupling effect of hydraulic load and mechanical behavior. Multi-stage hydraulic heads as well as various stress states are achieved by a newly developed apparatus to replicate infield sophisticated conditions. Sufficient specimen size is provided so that the well-graded test soil remains its natural gradation during constant water head permeability tests. The outflow of soil specimen was measured for each test. It is revealed that both the hydraulic and the mechanical effect result in a global decrease of gravelly material. A threshold of more than 6 MPa exists, indicating that the impact of further stress loading remains to a limited extent. In addition, no observation of obvious seepage failure illustrates that both hydraulic and mechanical loads are favorable to seepage prevention and corresponding countermeasures.

Untreated oil-contaminated water discharge from domestic and industrial sources has led to serious environmental pollution, especially in developing countries. Many technologies (e.g., floatation and coagulation, biological treatment, membrane separation, and so on) have been developed to treat effluents. Among them, the oil-water separation utilizing hydrophobized filtration beds can be expected to be a cost-effective and quick treatment technology. Previously, hydrophobized solid grains have been preliminary tested but applicability of hydrophobized porous grains have not been fully examined in oil-water separation system. This study aimed to characterize the hydrophobicity for artificially hydrophobized porous grains of autoclave aerated concrete (AAC) grains. The AAC grains (0.106 to 0.250 mm) were coated with two hydrophobic agent (HA) such as oleic acid (OA) and stearic acid (SA) at different concentrations (5 to 750 g of HA / kg of AAC grains). The OA-coated grains exhibited high hydrophobicity with HA > 50 g/kg while for SA-coated grains, hydrophobicity became significant from HA > 5 g/kg. Both OA- and SA-coated grains gave a rapid increase with increasing HA concentration and maximum contact angles reached 140–145o, suggesting that they had a high potential to apply in the filtration beds in oil-water separation system.

The water seepage damage in the chest-abdomen area of the Leshan Giant Buddha is significant, which causes the sandstone in the body of the Buddha to corrode and crack, makes the repair materials on the surface of the Buddha hollow and desquamate, and leads to the growth of biological damage. In this study, continuous monitoring and sampling of the water seepage in the chest-abdomen area of the Leshan Giant Buddha and the atmospheric precipitation were performed. The water seepage in the chest-abdomen area of the Buddha is primarily controlled by atmospheric precipitation and evaporation. The hysteresis effect of water seepage reflects that the bedrock fissure on the left is relatively developed with significant water transmissibility. During the atmospheric precipitation monitoring period, the average pH of atmospheric precipitation was 8.13, i.e., weakly alkaline. After 2009, the annual average pH of atmospheric precipitation for the Buddha was greater than 5.6 and increased year by year. The water seepage of the Buddha contained a large amount of ions. The chemistry type of water seepage in the chest-abdomen ares is calcium carbonate (CaCO3) and calcium sulfate (CaSO4). Rock weathering contributes more than 90% of the ions in the Buddha water seepage. The microscopic analysis of the rock shows that the main components of the rock are CaCO3 and SiO2, and there is obvious layered morphology, is easy to be dissolved in the presence of air and water. The composition of water chemical ions indicates that H2CO3 and H2SO4 are both involved in the process of the weathering of the sandstone.

Understanding the flow and contaminant transport process in rocks has received increased attention in the past two decades as these geological formations serve as potential sites to contain different types of wastes in geological repositories. In this paper, a discrete fracture network model is developed to understand the process of contaminant transport in a fractured rock mass. This model integrates a stochastic fracture generating algorithm for sedimentary rocks and a two-dimensional numerical model that simulates the flow and transport of a contaminant through the heterogeneous system of fractures. Further, the uncertainty in geological and transport properties of the contaminant are considered as random variables. The probability of concentration exceeding the permissible value at the endpoint is quantified by carrying out reliability analysis using the subset simulation method. The probabilistic framework developed in this study helps assess the behaviour of contaminant migrating through a complex heterogeneous system and provides a basis for gaining a level of confidence in the model results.