EISSN : 2051-803X
Published by: Thomas Telford Ltd. (10.1680)
Total articles ≅ 483
Latest articles in this journal
Environmental Geotechnics pp 1-10; https://doi.org/10.1680/jenge.21.00107
This study investigates changes in low-frequency attenuation responses of sands during microbial formation of soft viscous biofilms, or extracellular polymeric substances (EPS). The resonant column experiments were conducted with two model bacteria Shewanella oneidensis MR1 and Leuconostoc mesenteroides, while monitoring changes in the wave velocities and damping ratios associated with EPS formation in sands. The results show that the accumulation of soft, viscous EPS hardly changes the wave velocities, both the shear and flexural modes. By contrast, the low-frequency attenuations, both torsional and flextural damping ratios, show significant increases with the accumulation of highly viscous EPS. It is found that contribution of EPS to seismic responses of water-saturated sands is mainly limited to the pore fluid component, causing additional energy dissipation during wave propagation, but with no or minimal impact on skeletal stiffness or no involvement in seismic stress transfer. With these unique and unprecedented low-frequency seismic data of biofilm-associated sands, the results suggest that formation and accumulation of soft, viscous EPS or biofilm by bacterial activities can be detected by monitoring seismic attenuation and can also alter the seismic attenuation responses of sands, such as the cases under earthquake loading or blast-induced compaction.
Environmental Geotechnics pp 1-11; https://doi.org/10.1680/jenge.20.00076
The mechanical and permeability properties of rocks under unloading stress path and high temperature are critically important for hot dry rock. A series of unloading confining pressure and gas permeability tests were conducted on granite samples after heating and rapid cooling treatment. Five levels of temperature and three levels of confining pressures were used. The stress–strain curves of unloading confining pressure were obtained. The strength parameters and deformation parameters were further discussed and analysed. When the heat treatment temperature is higher than 600°C, the granite samples experience a significant degree of thermal damage. With the increase in heat treatment temperature and the decrease in confining pressure, the gas permeability increases. Beyond 600°C, the gas permeability of the samples increases significantly. With the increase in temperature, the internal friction angle decreases slightly from 25 to 400°C, while it increases beyond 400°C. The cohesion exhibits an inverse evolution. The initial unloading elastic modulus and deformation modulus decrease gradually during relief of confining pressure. The decrease rate of the deformation modulus increases with the increase in heating temperature. The experimental results could improve knowledge about the effect of thermal shock and stress on the physico-mechanical properties of granite.
Environmental Geotechnics pp 1-12; https://doi.org/10.1680/jenge.21.00018
This paper presents analytical solutions to estimate emissions of fluorotelomer alcohol (FTOH), a precursor of per- and poly-fluoroalkyl substance (PFASs), from landfill single and composite cover liners. Single liners comprise a compacted clay liner (CCL), geosynthetic clay liner (GCL) or geomembrane barrier (GMB). Composite liners included GMB underlain by a CCL or GCL. This paper shows that for a single liner, an intact GMB reduces the FTOH emission flux by three orders of magnitudes compared to a CCL and by two orders of magnitude compared to a GCL. Also, a composite cover liner reduces FTOH emissions by at least one-to-three orders of magnitude relative to a single GMB, depending on either the use of a CCL or GCL. The analytical solutions presented in this study can be used for the preliminary evaluation of different types of covers to mitigate FTOH emissions from landfills.
Environmental Geotechnics pp 1-9; https://doi.org/10.1680/jenge.20.00027
This paper presents results of an experimental program that was employed to investigate performance of biocovers made of food-waste compost in mitigating methane emissions from municipal solid waste landfills in a semi-dry environment. Five experimental columns containing biocover materials made of compost mixed with landfill intermediate cover soil at different compost/soil mixture ratios were exposed to methane inflow under ambient temperature over a period of three months. Methane removal efficiencies were determined based on methane content measurements using gas chromatography (GC), bacterial count and Scanning Electron Microscopy (SEM) performed on biocover samples over time. The biocover materials made of 70% compost and 30% soil demonstrated significantly higher methane removal efficiencies compared to other mixtures measuring an emission reduction of about 63%. The compost type and composition were also found to affect methane removal efficiency of biocover materials. These findings can be used for selection of compost type and compost-soil mixture ratio as biocovers materials.
Environmental Geotechnics pp 1-18; https://doi.org/10.1680/jenge.20.00066
This paper investigates the effect of different bio-based additives on the expansiveness of an Argentinian natural clayey soil (CR-clay). CR-clay was characterised to determine (a) the Atterberg parameters and other index properties, (b) the particle size distribution by laser diffraction, (c) the specific surface area (S e) and cationic exchange capacity by the methylene blue method, (d) the mineralogy by using X-ray diffraction, (e) the functional groups by Fourier transform infrared spectroscopy (FTIR) and (f) the free swelling and swelling pressure by using an odometer. Starches from potato, cassava, corn and rice flour; seeds and derivatives from flax, sunflower and quinoa; kraft lignin; and lignosulfonates were evaluated as soil stabilisation additives on the basis of measurements of Atterberg parameters. Reductions in the soil plasticity index (PI) between 10 and 60% were generally observed. Lignins exhibited a very good balance between the ability to improve soil stabilisation, low costs, environment-friendliness and availability. In particular, kraft lignin showed high performance as a CR-clay stabiliser with a PI reduction of 46%. The stabilisation mechanism of lignin and CR-clay blends was investigated using Z potential and FTIR. Based on the experimental results, lignins constitute promising alternatives to the additives used as stabilisers of expansive soils, particularly for reducing free-swell and swelling pressure.
Environmental Geotechnics pp 1-13; https://doi.org/10.1680/jenge.20.00013
For 12 years a waste deposit was in direct contact with the underlying ground. The waste, fly ash, was produced by electric arc furnaces of the Portuguese Iron and Steel Company. The subsoil consisted of waste rock spoils from an old coal mine site. The waste was transported to the site as part of a recovery operation. At the time of the recovery operation, the waste was classified as “inert”. Site investigations later performed showed that the waste was hazardous. The waste mainly consisted of high concentrations of lead and petroleum hydrocarbons, and there was no containment structure to confine the waste, which put local public health and the environment at risk. It was therefore recommended that the waste be moved to a hazardous waste landfill. In this paper, after the methodology used to study the waste disposal has been presented, it was followed by the methodology adopted for the reclamation of the site. Firstly, through the excavation of the waste deposited and the remediation of the subsoil by removing contaminated soil areas, whose depth did not exceed 0.75 m; and then, an on-site reuse operation was carried out by backfilling the natural soil that was covering the waste deposit.
Environmental Geotechnics pp 1-16; https://doi.org/10.1680/jenge.20.00137
This paper presents the determination of horizontal and vertical hydraulic conductivity in large particle sized tire derived aggregate (TDA) i.e. TDA with particle sizes over 50 mm, as substitute for gravel in landfill leachate collection and removal layers. The determination of hydraulic conductivity was completed under applied surface stresses from 56 kPa to 375 kPa, relating to 5 m to 40 m of waste over a TDA drainage layer in waste disposal facilities. Hydraulic conductivity was determined indirectly from measurements of air permeability. At the final applied stress, hydraulic conductivity was measured directly to compare with the values determined from the air permeability measurements. The Forcheimer addition to the typical Darcy’s equation of flow was used to account for effects of inertia from non-Darcian flows (as indicated from the Reynolds numbers). At all the applied stresses, after correcting for inertia, the equivalent horizontal and vertical hydraulic conductivity values for all TDA types tested were greater than 0.0001 m/s – a typical requirement for landfill drainage layers. Anisotropy in the hydraulic conductivity decreased with applied stress from as high as 10 at 56 kPa, to up to 2 at 375 kPa.
Environmental Geotechnics pp 1-11; https://doi.org/10.1680/jenge.19.00203
Compacted coal gangue is often used as subgrade soils in the South-central China. To further understand the effects of drying-wetting (D-W) cycles on the hydro-mechanical behavior of compacted coal gangue subgrade, this paper presents a series of laboratory test results on reconstituted coal gangue subjected to multiple D-W cycles. The effect of vertical load and compaction parameters on the soil deformation behaviors during hydraulic loading are fully discussed. Based on the laboratory investigations, the shrinkage strain was found to decrease with the increase of the initial dry density, however, it increased with the increase of vertical load. Experimental results also revealed that the variation of soil water content is more pronounced in the 1st D-W cycle. The characteristics of the void ratio and water content change during D-W cycles was investigated and the shrinkage behavior (e - w) was obtained. Significant hysteresis was detected during the D-W cycles, and the size of hysteresis loop was found to decrease with the increase of D-W cycles while increase with the increase of vertical load. In addition, the D-Ws cycles were found to influence the pore volume at the microscopic scale, where both the volume of inter-aggregate pore and intra-aggregate pore were found to decrease as the hydraulic loading increased.
Environmental Geotechnics pp 1-11; https://doi.org/10.1680/jenge.21.00014
The use of microbially induced carbonate precipitation (MICP) is known to be effective in the solidification and stabilization of fly ash that results as a by-product of municipal solid waste incineration (MSWI). In the search for more adaptable and applicable bacteria for MICP fly ash treatment, five species of bacteria were isolated from the nursery soil. The biochemical characteristics of the five bacteria were tested to assess their adaptation to the environment of fly ash. The geotechnical properties and heavy metal leaching concentrations of the fly ash treated by the five bacteria were also tested to evaluate solidification and stabilization effects. Results were compared with the commonly used bacteria Bacillus pasteuril. The Ensifer adhaerens strain outperformed other strains, including B.pasteuril, in environmental adaptation, particle solidification and in the heavy metal stabilization of fly ash. Further MICP treatment tests under different bacterial concentrations, curing conditions and fly ash void ratios were carried out on this strain to investigate the influence of various factors on MICP efficiency. Both the MICP and the pozzolanic solidifying properties played important roles in the solidification and stabilization mechanisms, where the best solidification effect occurred at bacterial concentration of 14.92×107 cells/mL and fly ash void ratio of 0.724.
Environmental Geotechnics pp 1-12; https://doi.org/10.1680/jenge.20.00065
This research aims to enhance the adsorption capacity of local clay using a fly ash-based geopolymer representing active-passive liner materials. Clay-fly ash geopolymers were synthesized from the mixtures containing 40, 50 and 60% fly ash to the total solid mass and then activated by 8, 10 and 12 M NaOH solutions. Batch experiments were conducted for the removal of lead, Pb(II), and zinc, Zn(II), from leachate at ambient temperatures of 24°C after 90 min contact time. Then, for the clay-fly ash geopolymer exhibiting the best adsorption capacity, the effects of contact time, initial concentration of solutes and curing time on its adsorption capacity were thoroughly studied. The best performance for the adsorption of Pb(II) and Zn(II) occurred with the lowest percentage, i.e. 60%, of clay in the synthesized geopolymers due to the diminished competitor ions concentration released by the alkali activation of clay. There, moreover, existed a notable correlation between porosity and adsorption capacity of the adsorbents to develop the eminent adsorption of the heavy metals, particularly for Pb(II) removal. The study of Langmuir and Freundlich isotherms also showed that the adsorption of Pb(II) is described by homogenous surfaces, while the heterogeneous surfaces characterize Zn(II) removal. That refers to the different adsorption process for the removal of Zn(II).