Results in Journal Environmental Geotechnics: 488
(searched for: journal_id:(492603))
Environmental Geotechnics pp 1-12; https://doi.org/10.1680/jenge.21.00055
The objective of this study is to develop a novel method for producing polymerized bentonite (PB) that will have high swelling capacity and low permeability when treated with aggressive cation solutions. PBs with polymer to bentonite ratios of 0.1 (0.1PB) and 0.2 (0.2PB) were produced using natural sodium bentonite (UB) and two monomers (acrylic acid (M1) and acrylamide (M2)) by a free radical polymerization method. The optimum conditions for polymerization were M1/M2 ratio of 0.5, initiator (I) to monomer I/(M1+M2) ratio of 0.5%, and a pH of 6. Instead of using nitrogen gas, a vacuum pressure was used to remove oxygen during the polymerization process. The results of X-ray diffraction (XRD) test showed that 0.2PB is an intercalated composite. The results of free swelling index (FSI) and swelling pressure tests indicated that the PBs have higher swelling capacities than those of UB (e.g., In 0.6 M NaCl solution, the FSIs of PBs were more than 24 mL/2g). In terms of consolidation behaviours, the compression indexes of PBs were higher than those of UBs. For given void ratios, the permeabilities of PBs calculated from the results of consolidation tests were smaller than 10−10 m/s for 0.6 M NaCl solution.
Environmental Geotechnics pp 1-14; https://doi.org/10.1680/jenge.21.00091
The revitalization of the global economy after the COVID-19 era presents Environmental Geotechnics with the opportunity to reinforce the need for a change in paradigm toward a green, circular economy and to promote aggressively the use and development of sustainable technologies and management practices. This paper aims to assist in this effort by concentrating on several thematic areas where sustainability solutions and future improvements are sought. These include the re-entry of construction and demolition waste, excavated material, industrial waste, and marine sediments into the production cycle and the reuse of existing foundations. Despite the recent trend in advanced countries toward recycling and waste-to-energy thermal treatment, landfills still constitute the most common municipal solid waste management practice, especially in low-and-middle-income countries, and technological solutions to improve their environmental footprint are presented. At the same time, remediation solutions are required to address the multitude of contaminated sites worldwide. Advanced developments that incorporate environmental, economic, and social dimensions are expounded, together with sustainable ground improvement solutions for infrastructure projects conducted in soft and weak soils. The topic of thermo-active geostructures concludes this paper, where, apart from their infrastructure utility, these structures have the potential to contribute as a renewable energy source.
Environmental Geotechnics pp 1-10; https://doi.org/10.1680/jenge.21.00012
Physical and chemical stability of tailings deposits sometimes have conflicting priorities, yet they are rarely examined congruently in a comprehensive research program. This paper presents an investigation of the combined geotechnical and geochemical behaviour of two samples of diamond ore tailings. Detailed basic and advanced geotechnical laboratory characterization tests were conducted to evaluate the particle size distribution, hindered sedimentation, compressibility, hydraulic conductivity and undrained shear strength of both tailings. Furthermore, duplicate specimens to evaluate the drainage effluent's geochemical compositions were conducted to evaluate compliance with regulatory concentration criteria. The cation and anion concentrations of the expelled water were analyzed at different consolidation stages along with other basic geochemical index properties such as pH, redox potential and electrical conductivity. Both the geotechnical large strain consolidation testing and the geochemical pore fluid collection were performed in a controlled-temperature environment to represent the cold climatic regime at the mine site. Tests were performed in a walk-in freezer with a nominal ambient temperature of 4-5°C. Moreover, the drainage effluent from the large strain consolidation geochemical duplicates was collected using an innovative sampling system that ensured the sample was not exposed to the atmosphere. The geotechnical and geochemical implications of both tailings treatments are discussed.
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, Volume 8, pp 467-479; https://doi.org/10.1680/jenge.18.00174
The use of polymers can change specific properties of natural soils. This study analyses the interaction of a natural fine sand, a clayey soil and anionic polyacrylamide (APAM). The laboratory results show that APAM, a superabsorbent polymer, increases the plasticity and the capacity of water absorption of a clay-APAM and a sand-clay-APAM compacted composite. Free swelling and swelling pressure also increase with addition of APAM. Sand-clay-APAM composite shows a higher uniaxial compressive strength and slight reduction of hydraulic conductivity. Microstructural analysis confirms the aggregation capacity of APAM and a reduction of the accumulated pore volume which minimise liquid infiltration and soil erosion. Results demonstrated that the clay-APAM and a sand-clay-APAM composites can be effective as liners and covers respectively in a landfill system.
Environmental Geotechnics, Volume 8, pp 452-466; https://doi.org/10.1680/jenge.18.00168
Mine tailings management systems (TMS) consist of a web of inter-related sub-systems across multiple processes and disciplines. Conventional predictive models simulate individual physical processes but lack integration with the overall TMS. A dynamic system modeling approach was adopted to develop a model capable of simulating a TMS to facilitate the evaluation of operating strategies, design alternatives and dewatering technologies. Using a multitude of process-based, empirical, and qualitative formulations, the model incorporates major components of a TMS including tailings production, dewatering, deposition and impoundment water balance. Individual model processes (e.g. consolidation and deposition) were verified using experimental, analytical, or numerical data sets. A tailings plan from a hard rock mine was then simulated to evaluate the model. The simulated tailings deposit and water cap elevations as well as total impoundment volume were found to be within 5% deviation of the mine data, indicating the model is capable of simulating a TMS.
Environmental Geotechnics, Volume 8, pp 480-494; https://doi.org/10.1680/jenge.19.00051
New analytical solutions are presented for the assessment of the impact of contaminant transport through landfill liners on groundwater quality under steady-state conditions. These solutions can be applied to evaluate the equivalency and the effectiveness of landfill liners, even those that include a geomembrane, taking into account the presence of a natural attenuation layer interposed between the engineered barrier and the underlying aquifer. The impact of a contaminant on groundwater quality is quantified through the determination of the contaminant concentration along the horizontal direction of the groundwater flow for the case of thin aquifers that are only a few meters thick. For the case of thick aquifers, both a closed-form analytical solution and a step-by-step numerical solution are provided for the calculation of the variations in the contaminant concentration in horizontal and vertical directions within the aquifer.
Environmental Geotechnics, Volume 8, pp 430-441; https://doi.org/10.1680/jenge.18.00201
Environmental Geotechnics, Volume 8, pp 442-451; https://doi.org/10.1680/jenge.19.00028
Organic matters commonly exist in the subsoil within the tree rooting zones. The organic content of soil has been known to affect soil properties. In this study, the soil organic contents at various locations around trees were investigated and found to be variable due to the ground flora and tree roots. The range of soil organic content for the current study was between 0.9–12.5%. The objective of this study was to investigate the effects of the organic content on the shrinkage and Soil-Water Characteristic Curve (SWCC) of the soils during rainy and dry seasons when water content of the soil changes. Soil samples were collected from two locations on Singapore Island at depths of 0.1 m and 0.3 m, one site on the western side of the island and the other site at a coastal area along the eastern shore. Centrifuge was used to measure the water content of the specimens at suction up to 250 kPa and chilled-mirror psychrometry was used for the higher suction. Shrinkage tests were also conducted to obtain the shrinkage properties. The results show that organic content influenced the shrinkage and SWCC where a higher organic content was associated with a greater shrinkage rate and a higher suction corresponding to the residual water content. For the finer soils, a higher organic content comes with a lower air-entry value.
Environmental Geotechnics, Volume 8, pp 495-505; https://doi.org/10.1680/jenge.18.00096
Air sparging is a remediation technology for treating soil/groundwater contaminated with volatile organic compounds (VOCs). VOC removal during air sparging is rendered less effective, because of the random formation of air channels, creating preferential paths for airflow, thus, limiting remediation to these channels, referred to as a zone of influence (ZOI). Pulsation is a popular method used to improve the effectiveness of air sparging through cyclic operation, with the hope air channels would form elsewhere. Pulsation makes air sparging more time-consuming. This paper studies the effects of one cycle of pulsation and air pressure on airflow pattern and presents the laboratory study to investigate the effects of initial and further increases in the injected air’s pressure on airflow pattern within a glass-bead medium used as a medium analogous to the soil. Digital images of airflow patterns were collected; these images show a larger radius of influence (ROI) and ZOI due to the initial air-pressure increase, especially when a higher overburden pressure (i.e., the stress due to the partially saturated layer on top of the saturated soil-simulant layer) exists above the water-saturated zone. Further air-pressure increases seem to have no measurable effect on the ROI and the shape of the ZOI.
Environmental Geotechnics, Volume 8, pp 428-429; https://doi.org/10.1680/jenge.2021.8.7.428
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 1-11; 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 1-9; 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 1-11; https://doi.org/10.1680/jenge.21.00061
The Hydrogen Transfer (HT) experiment, located at the Mont Terri underground rock laboratory in Switzerland, is an in situ experimental study of the interactions and transport of hydrogen injected into a borehole installed within Opalinus Clay, a claystone formation. A python-based model was developed to analyse and model the experimental data, for diffusion of dissolved gases and solutes in claystone pore water, for thermodynamic modelling of gas-water-solid phase equilibria in the injection interval and for simulations of chemical equilibria and reaction kinetics in claystone and injection interval. The developed model reproduces the temporal evolution of gas pressure, composition and solute concentrations measured in situ with a minimum set of adjustable parameters. The effective diffusion coefficients for dissolved gases in Opalinus Clay derived by the modelling of experimental data were found to be very close to values measured in other experimental studies. It was discovered that an accurate description of the temporal variations in hydrogen injection and temporal changes in the inflow of formation water is essential for modelling of microbial mediated hydrogen consumption in the injection interval.
Environmental Geotechnics pp 1-12; https://doi.org/10.1680/jenge.21.00077
Experiments were conducted to evaluate hydraulic conductivity of five geosynthetic clay liners (GCLs) permeated with four synthetic coal combustion product (CCP) leachates (Ionic strength = 473 mM to 4676 mM). One of the GCLs contained conventional sodium bentonite (Na-B) and the other four GCLs contained bentonite-polymer (B-P) composite with polymer loading ranging from 0.5% to 12.7% (B-P-0.5∼B-P-12.7). Hydraulic conductivity tests were conducted at 20 kPa until reaching hydraulic and chemical equilibrium, and then the effective confining stress was increased incrementally from 20 to 100, 250, and 500 kPa. Hydraulic conductivity of B-P GCLs with high polymer loading showed faster decreasing trend than that of Na-B and B-P GCLs with lower polymer loading as effective confining stress increased. Additionally, the hydraulic conductivity of GCLs permeated with synthetic CCP leachate with ionic strength of 473 mM decreased significantly as the effective confining stress increased, whereas the GCLs permeated with aggressive CCP leachate (e.g., ionic strength = 4676 mM) had limited reduction in hydraulic conductivity at elevated effective confining stress.
Environmental Geotechnics pp 1-17; https://doi.org/10.1680/jenge.21.00065
A series of large scale direct shear tests is used to examine the effectiveness of smooth, textured, and structured surface geomembranes (GMBs) with different soil subgrades for heap leach pads applications. Four different subgrades, including sand, two different coarse-grained underliners, and a clayey soil representing the layers directly underlying the GMB liner in heap leach pads, are used to examine the shear strength of the GMB-Subgrade interfaces at normal stresses between 50 and 1000 kPa. It was found that increasing the normal stresses can change the mechanisms contributing to the shear resistance at the interface. This resulted in a statistically insignificant increase in the interface friction of the GMB-Granular soils interfaces when using GMBs with surface roughness relative to the smooth GMB. Furthermore, depending on the type of subgrade, establishing the shear envelopes over a wide range of normal stresses was found to overestimate or underestimate the shear strength at the field stresses even when linear regressions present the best fit for the data.
Environmental Geotechnics pp 1-12; https://doi.org/10.1680/jenge.20.00058
Three landfill gas generation models following two established kinetic pathways–first order decay (LandGEM and IPCC) and sigmoidal growth (Modified-Gompertz) are considered and fitted against a range of methane generation data generated from large-scale degradation experiments of seven well-characterized municipal solid waste (MSW) specimens that were operated in an identical manner. The parameter values are obtained for specimens having significantly different compositions, ranging from “waste-rich” to “soil-rich”. Model parameters related to methane yield potential, mass of degraded decomposable organic carbon and daily methane yield are found to be proportional to the biodegradability of the specimens. However, parameters related to decay rate and time lag in the methane generation process are not significantly influenced by waste composition. This study contributes to guiding estimates of biogas generation model parameters based on waste composition data.
Environmental Geotechnics pp 1-9; https://doi.org/10.1680/jenge.19.00222
With the exception of the engineering properties of kaolinite, bentonite, silt and sand, little attention has been paid to how the hydrophysical properties of red clay vary with pH value, even though acid contamination of red clay occurs widely. The purpose of this paper is to investigate the laws and mechanisms for the hydrophysical properties of red clay treated with dilute hydrochloric acid. Tests were performed on a natural red clay from South China to determine how hydrochloric acid influences the hydraulic conductivity, expansibility and shrinkage. The test data are of the mineral composition, main metal oxide and zeta potential of the red clay before and after being soaked in various acidic solutions having pH of 3, 4, 5, 6.5. The results show that the consistency decreased with pH value for decreasing zeta potential. In addition, the hydraulic conductivity first decreased and then increased, but the expansibility and contractility went the other way, as the pH value of solution decreases. These phenomena depend on the decrease of zeta potential, the water intensity entering the montmorillonite crystals cells, and the formation of open void.
Environmental Geotechnics pp 1-22; https://doi.org/10.1680/jenge.20.00177
This study presents a preliminary assessment of the environmental impact of field-scale underground coal gasification (UCG) targeting deep-buried seams by studying the fate of the UCG products in the reactor vicinity. A series of simulation scenarios are conducted in three deep (900 m) areas of specific interest, i.e. South Wales coalfield (UK), Upper Silesian coal Basin (PL), and Ruhr mining district (DE), to investigate the gaseous and dissolved chemicals’ transport. The results indicate that the syngas propagation is limited to 2.0 m in the reactor’s vicinity after 30 days, except that 4.4 m in shale (overburden) of the UK site. Transport of the dissolved chemicals, via diffusion, is limited to 2.0 m without considering adsorption and less than 0.5 m when the adsorption is considered after 10 years. Moreover, the effect of hydrology condition, strata adsorption properties, and the thermally-induced change of rock porosity and permeability on the propagation of UCG products are studied. The results suggest that unacceptable risks to the environment are unlikely to arise if standard operating conditions are applied, offering a great prospect of deep coal seams to be considered for UCG. This study also provides insights into the environmental evaluation for other potential UCG projects.
Environmental Geotechnics pp 1-10; https://doi.org/10.1680/jenge.20.00105
Heat generation occurs in landfills due to the degradation of organic matter. This paper aims to evaluate the heat generated due to the organic matter degradation of synthetic municipal solid waste using a bioreactor. A double-layered bioreactor is developed for the waste degradation test, during which the waste temperature, ambient temperature, gas emissions and total degraded organic matter are measured. The waste degradation tests last more than 350 hours and indicate peak values for both the waste temperature and the rate of gas emission. The heat generated from waste degradation is determined by accounting for increases in the waste temperature, gas emissions and bioreactor conduction. The total heat generated per unit mass of the dry organic matter ranges from 1503 kJ to 1776 kJ, which shows reasonable comparison results with the reported heat values. The variation in the total heat generated with waste degradation time is well predicted by an empirical formula, in which the heat parameters are correlated with the times of the peak waste temperature and peak heat generation rate.
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).
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 1-13; 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.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, Volume 8, pp 365-366; https://doi.org/10.1680/jenge.2021.8.6.365
Environmental Geotechnics, Volume 8, pp 392-400; https://doi.org/10.1680/jenge.18.00153
There is a need for an eco-friendly in situ reversible permeability control that reduces the number of artificial materials used to achieve a saturated sand layer. This study investigates such a control using a method that causes calcite precipitation and decalcification based on the metabolism of carbon sources; this generates carbon dioxide and organic acid, and creates and detaches a biofilm using dry yeast and sodium hypochlorite. A pilot test determined the optimal chemical composition for this from a few different concentrations of carbon sources that begin the permeability reduction and recovery process. Following this, the main test (the permeability test) was conducted on a water sample taken from an agricultural area, which was combined with chemicals and dry yeast in a permeameter column. Permeability tests were carried out under three conditions (untreated, treated, and treated combined with a biofilm detachment phase). Our results suggest that (1) calcite precipitation induced by microbes, combined with bio-clogging, can control the reduction in soil permeability, and (2) a biofilm remover (sodium hypochlorite) and decalcification based on the organic acid created from the metabolism of carbon sources effectively recovered the soil permeability to its initial state.
Environmental Geotechnics, Volume 8, pp 382-391; https://doi.org/10.1680/jenge.18.00089
The application of biopolymers as eco-friendly stabilizers to strengthen soils has received increasing attention in recent years. This paper presents an experimental and numerical investigation of using xanthan gum, a green biopolymer, to stabilize mine tailings (MT) for dust control purpose. Impact tests that simulate the saltation process during wind erosion were carried out to evaluate the effect of xanthan gum on the impacting resistance of MT, which is directly related to dust resistance. The impact test results show that the weight loss due to grain impacts is significantly reduced for biopolymer treated MT compared to the untreated, more biopolymer leading to greater reduction. The improved dust resistance of MT after biopolymer treatment may be attributed to the protective biopolymer coating formed at the surface of treated MT, which imparts the MT with a dense structure and enhanced cohesion, and therefore improves the impacting resistance. Numerical simulation using discrete element method (DEM) was performed to explore the underlying mechanisms of how biopolymer increases dust resistance of MT. The simulation results show that the bonding strength between MT particles increases linearly with biopolymer concentration; more biopolymer induces larger inter-particle bonding and therefore increases impacting and cracking resistance of MT.
Environmental Geotechnics, Volume 8, pp 367-381; https://doi.org/10.1680/jenge.18.00063
The mechanical behavior of soils overlying weathered bedrock is often a concern when it comes to the risk of sinkhole occurrence. Cavities often form near the interface between cover soil and fissured bedrock, and propagate upwards with internal soil erosion, ultimately resulting in surface collapse known as sinkhole. This paper presents and discusses the mechanical behavior of sinkholes by investigating the stability associated with the size and depth of cavity. Two failure modes considered in this study corresponds to tensile failure and excessive yielding around a subsurface cavity. Numerical modeling with the finite difference (FD) software (FLAC) was employed to determine the stress distributions and deformations around the cavity. The results of numerical analyses were used to quantify the effects of factors affecting sinkholes as bedrock depth, cavity size, overburden thickness, and soil strength. The results also illustrate the yielding behavior, which is related to a cover-subsidence sinkhole with a gradual depression over time but no structural collapse. The analysis result exhibits that the critical overburden thickness of around 25 m that turns the yielding condition from unstable to stable.
Environmental Geotechnics, Volume 8, pp 401-407; https://doi.org/10.1680/jenge.18.00186
Compression behaviour of soils is related to many geotechnical engineering problems e.g. ground subsidence, foundation deformation, embankment failure, etc. So far, research on coupled effects of matric suction and temperature on compression behaviour of soils are very limited. The aim of this study was to investigate the compression behaviour of intact and compacted loess at various matric suctions and temperatures. It is found that for both intact and compacted loess, at various suctions, preconsolidation pressure decreases with increasing temperature (thermal softening). Because the double layer repulsion force R increases with increasing temperature. The thermal softening of preconsolidation pressure at zero suction is more significant than that at suction of 100 kPa. This is likely because more water exists in the soil specimen at a lower suction. Heating-induced decrease of viscosity of water affects particle movement and the yielding of soil skeleton. Moreover, it is found that suction effects on thermal softening of preconsolidation pressure of intact loess is more significant than that of compacted specimen.
Environmental Geotechnics, Volume 8, pp 416-427; https://doi.org/10.1680/jenge.18.00139
Improving soil strength by physical and chemical methods is a common practice in geotechnical engineering. This study investigates chemical stabilization of soil with calcium oxide, CaO, to modify the physical and chemical properties of clay materials, which can rapidly transform a material with poor mechanical properties into one with favorable properties for different surface working conditions and good short-, medium-, and long-term geotechnical behavior and its effects on the environment. Effects that affect the site and other regions beyond the airport construction polygon. The main advantages measured are. The mitigation (27.6%) of the exploitation of borrow pits, the use (81.1%) the natural materials from site, and the mitigation (11.1%) of the transport demand. The analyzed materials are lacustrine clay soils (cohesive soils) with low strength, high compressibility, and moisture contents of 55%, 100%, and 170% from ex-Lake Texcoco in the basin of the Valley of Mexico. In this study, the authors performed Atterberg limits tests, compaction tests, unconfined compressive strength (UCS) tests, California bearing ratio (CBR) and expansion tests, Eades and Grim tests, and quantitative chemical analyses by X-ray fluorescence (XRF) and X-ray diffraction (XRD). The optimum lime contents for the analyzed samples were 5% and 15%. The UCS of the mixtures was analyzed for curing periods of 7, 14, 21, 28, and 69 days, which resulted in a final compressive strength (UCS) greater than 2000.0 kPa, CBR >50%, and expansion <0.5%. In addition, two test platforms previously constructed on the grounds of ex-Lake Texcoco with in-situ stabilized soil in 2015 and 2016 were studied.
Environmental Geotechnics, Volume 8, pp 408-415; https://doi.org/10.1680/jenge.18.00205
This paper presents a study on the hydraulic conductivity of degraded municipal solid waste (MSW) and its variations with different degradation ages, using a self-made combined permeability–compression test apparatus to perform hydraulic conductivity tests. The principal outcomes were as follows. (1) The hydraulic conductivity decreased gradually with increases in the pressure, density, and degradation age. The relationship between the logarithmic hydraulic conductivity and each parameter could be formulated as a linear function, and the fitted coefficients were >0.92, >0.88, and >0.79, respectively. (2) A hydraulic conductivity – pressure – density – degradation age mathematical model was established. These results can be used to provide an empirical basis to analyze the hydraulic conductivity of MSW landfills and design leachate drainage systems.
Environmental Geotechnics, Volume 8, pp 334-344; https://doi.org/10.1680/jenge.18.00009
Controlling swelling and shrinkage deformation of the expansive soil is essential for the design of earth structures surrounding by expansive soils. The swelling and shrinkage deformation could induce severe damages (i.e., cracks and/or distortion) to infrastructures, for example, embankments, pavements, pipelines, etc. In this study, a series of laboratory tests and a field trial on the Huai’an expansive soils were conducted to investigate its shrinkage-swelling cycle characteristics. A technology of combining quicklime-stabilization and surcharge pressure was proposed to limit Shrinkage-Swelling deformation of the Huai’an expansive soil in a highway embankment project. The experimental and field test results show that (1) the swelling potential of the Huai’an expansive soil increased with an increase of number of drying-wetting cycles without surcharge pressure; (2) the swelling potential decreased with an increase of magnitude of surcharge pressure; (3) adding quicklime into the Huai’an expansive soil combining with surcharge pressure could reduce the swelling potential significantly; and (4) the shear strength of expansive soil samples decreased as the number of drying-wetting cycles increased. The measured settlement from the field test indicated that the proposed technique can reduce the swelling potential and control the heaving of the Huai’an expansive soil effectively.
Environmental Geotechnics, Volume 8, pp 345-356; https://doi.org/10.1680/jenge.18.00100
This paper aims to discuss the influence of the coupled deformation of unsaturated soil on the slope stability under rainfall condition. Numerical soil column tests were first performed to display the seepage deformation, and the pore water pressure (PWP) distribution differences of the coupled analysis. Comparative analyses were done for three different analysis cases (i.e., uncoupled analysis, coupled analysis without considering the permeability coefficient (Ks) change, and coupled analysis considering the Ks change) under different infiltration intensity. The analysis results show that the coupled deformation lead to different PWP distribution and factor of safety (FS) profiles in the shallow slope from the uncoupled analysis, and the Ks change caused by seepage deformation plays an important role. There is a great risk for accurately assessing the shallow slope state as to the uncoupled analysis and the coupled analysis without considering the Ks change.
Environmental Geotechnics, Volume 8, pp 357-364; https://doi.org/10.1680/jenge.18.00081
Nano Zero-Valent Iron (nZVI) is a versatile nanomaterial that can not only efficiently remove contaminants in soil, but also improve the soil’s geotechnical strength by changing their physicochemical properties. Inert solid mineral particles are the most common ingredients in soils, they present universal surface modification after the nZVI treatment. This study presents an investigation on the morphological and mineral features of nZVI induced iron mineral precipitations on quartz particles. Lead was employed as the artificial contaminant, while quartz was used to mimic the inert solid mineral particles in soil. Scanning Electron Microscope (SEM), Digital Image Analysis (DIA), Transmission Electron Microscopy (TEM), laser particle size analyzer, X-ray diffraction (XRD) and Raman spectrum were carried out for the characterization. The results indicate that iron minerals precipitated heterogeneously on the surface of quartz particles with plush-like and flake-like structure. They are made of deuterogenic plumbiferous minerals and ferriferous minerals. XRD analysis demonstrated that these minerals are amorphous. The curly flake-like mineral clusters were scatteredly distributed on the surface of quartz along with the of corroded nZVI aggregation. The thickness of the curly flake-like precipitation varied from 20 nm to 60 nm, and 20 nm to 35 nm for the plush-like precipitation. The generation of these iron mineral precipitations led to a slight increase in the average particle size and a decrease in the surface area of the soil. However, no clear difference in the shape and roughness of quartz was found after the nZVI treatment. This study is provided to improve the understanding of mass transfer from nZVI to inert solid particles in soil and its effect in soil improvement.
Environmental Geotechnics, Volume 8, pp 324-333; https://doi.org/10.1680/jenge.17.00097
Impervious coating treatment is an original technology which consists of the coating of soil and solid waste by particle units with an impervious coating material (a sealing material) containing water-absorbent polymers. The elution of attached substances, such as heavy metals, from the surface of soil particles will be suppressed. This is because each particle is uniformly coated with the sealing material. Furthermore, because the sealing material swells, due to the absorption of pore water, and fills the void spaces of the soil and solid waste, the water interception performance of the treated soil can be expected to improve. Through laboratory experiments, this study evaluates the basic characteristics, such as the elution of heavy metals and the hydraulic conductivity, of soil and solid waste that have been treated with an impervious coating in order to investigate their reutilization.
Environmental Geotechnics, Volume 8, pp 307-308; https://doi.org/10.1680/jenge.2021.8.5.307
Environmental Geotechnics, Volume 8, pp 309-317; https://doi.org/10.1680/jenge.18.00088
This study explores a new method of in situ debris–cement mixing through laboratory and field experiments to reuse dredged postdisaster debris for the ground improvement of banks in alpine wild creeks. Different mixing ratios of water, cement, and in situ debris were subjected to laboratory and field testing so that the relationships between the compressive strength, water–cement–aggregate ratio, and sand content of the test specimens could be determined. The results were then applied to field work in wild creeks. Furthermore, the compressive strength desired for ground improvement in alpine wild creeks through the mixing method is proposed. Considering cost-effective and eco-environmental conditions, a cement–aggregate ratio of 1:12, compressive strength of 400–1200 psi, slump of approximately 15 cm, and sand content of less than 60% are proposed. Overall, the in situ debris–cement mixing method can be practically employed for debris recycling and ground improvement to protect banks in alpine wild creeks.
Environmental Geotechnics, Volume 8, pp 318-323; https://doi.org/10.1680/jenge.18.00079
Stone columns are used to enhance the bearing capacity of poor ground and reduce the compressibility of soft clays. The aim of this study is to evaluate the effectiveness of stone columns with different waste materials on the performance of loose sand. The study provides guidelines for the selection of the most effective and economical material for stone column construction. In this study, waste materials from different construction sites were selected: shredded bricks, crushed waste stone and crushed old concrete. The stone columns were constructed with these waste materials. Load-settlement response of the unreinforced and reinforced soils with single and group of stone columns constructed with these waste materials were determined under the same loading conditions. The obtained results showed a very good improvement in the settlement behavior of the loose sand. As a conclusion, local waste building materials can be used effectively for stone column construction. The use of these waste materials will contribute recycling and environmental sustainability.
Environmental Geotechnics, Volume 8, pp 244-245; https://doi.org/10.1680/jenge.2021.8.4.244
Environmental Geotechnics, Volume 8, pp 274-281; https://doi.org/10.1680/jenge.17.00108
Microbial induced calcite precipitation (MICP) using ureolytic bacteria have been investigated to improve engineering properties of soil. Urease, produced by the ureolytic bacteria, can hydrolyze urea to drive the biogeochemical reaction in MICP. The goal of this study was to use EC and pH change value of urea hydrolysis test as an indicator to monitor ureolytic activities of bacteria before MICP process and using this indicator to maintain a consistent MICP treatment. Laboratory experiments were conducted to establish the relationship between the EC and pH value and unconfined compression strength (UCS) of MICP-treated soil. The EC and pH value of the mixed solution were measured after adding bacterial suspension into urea solution. Then, the bacterial suspension was mixed with sand sample and cementation media to drive MICP process. The results showed that once the bacterial suspension was mixed with urea, the EC and pH value of the mixed solution increased immediately due to the urea hydrolysis. The optimum EC and pH value at 60 minutes were found to be 1.50 to 1.80 mS/cm and 8.82 to 9.02, respectively, to achieve consistent UCS performance of MICP treated specimens with 0.25 M Ca cementation media.
Environmental Geotechnics, Volume 8, pp 295-306; https://doi.org/10.1680/jenge.18.00099
Environmental Geotechnics, Volume 8, pp 264-273; https://doi.org/10.1680/jenge.18.00146
Environmental Geotechnics, Volume 8, pp 246-254; https://doi.org/10.1680/jenge.15.00055
Environmental Geotechnics, Volume 8, pp 282-294; https://doi.org/10.1680/jenge.18.00087
Environmental Geotechnics, Volume 8, pp 255-263; https://doi.org/10.1680/jenge.16.00039
Environmental Geotechnics pp 1-9; https://doi.org/10.1680/jenge.19.00233
This study examines the effects of different types of wood chips on characteristics of the unconfined compression (UC) of geomaterials composed of wood chips and converter steelmaking slag. Three types of wood chips—coconut fibre, hinoki, and larch—were used to form specimens through the compaction of a mixture of wood chips, steelmaking slag, and blast-furnace fine slag powder at predetermined ratios. UC tests were conducted on the specimens after they were cured for seven, 28, and 84 days. The following observations were made: (1) The characteristics of UC changed drastically with the shape and ratio of wood chips mixed with slag. (2) When the durations of curing were different, the mixing of wood chips had different effects on the mechanical properties of the composite material. (3) Even when the ratio of wood chips in the mixture was > 33 vol.%, the UC strength increased due to curing regardless of their shapes. (4) The mixture of wood chips and slag had lower strength than slag only, but became a tough geomaterial. In addition, its UC strength was lower than that of slag only but not significantly lower than that of ordinary geomaterials.
Environmental Geotechnics pp 1-14; https://doi.org/10.1680/jenge.20.00089
As heavier rainfall intensities are expected in the future, it is important to employ preventive measures for anticipated possibility of residual soil slope failures. This study primarily focuses on the principles of unsaturated soil mechanics to establish an appropriate framework for adaptation measures against extreme rainfall conditions. These adaptation measures consist of the development and evaluation of slope susceptibility maps as well as the planting of vegetation for critical slopes based on regional stability analyses of residual soils within Bukit Timah Granite and Old Alluvium in Singapore. In this study, slope susceptibility maps were developed for three zones of residual soils within Bukit Timah Granite and Old Alluvium in Singapore. The pore-water pressure distributions and factors of safety (FS) within each zone were obtained from Transient Rainfall Infiltration and Grid-Based Regional Slope Stability Analysis (TRIGRS) and Scoops3D, respectively. Results from the slope susceptibility maps were verified against 2-D numerical analyses. The 2-D numerical models were verified through instrumentation data. The results from slope susceptibility maps agreed with the results from 2-D numerical analyses. In addition, the inclusion of vegetation at the slope face was concluded to be an effective slope stabilisation measure from the simulated 2-D numerical analyses.