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The amount of municipal solid waste (MSW) has increased significantly in developing countries. Landfilling is the commonly used treatment for the disposal of MSW. The MSW contains more food waste in developing countries than in developed countries. This work analyzed the degradable components of MSW with different food contents. A theoretical model was introduced to analyze the coupled hydro-mechanical-chemical interactions in the landfilled MSW. The impacts of the degradation on the properties of high-food-waste-content MSW were reviewed, including the compression behavior, strength parameters, and hydraulic conductivity. The major cause of geoenvironmental issues in high-food-waste-content landfills are rapid leachate and landfill gas generation. A practical model for analyzing leachates and gas production was presented. Landfills in China were used as an example to describe engineering measures for leachate drainage and landfill gas collection. These methods proved successful in solving geoenvironmental issues of landfills with high leachate levels. The experiences are useful for engineers who face similar issues with high-food-waste-content landfills in developing countries. more...

In order to study the flushing efficiency of different leaching agents on the mixed contaminated soil in landfill, five surfactants (SDS (sodium dodecyl sulfate), SDBS (sodium dodecyl benzene sulfonate), Tween 80, RL (rhamnolipid), and saponin) and three chelants (EDDS ([S,S]-ethylene-diamine-disuccinic acid), EDTA (ethylene- diaminetetraacetic acid), and CA (citric acid)) were selected to carry out batch tests and one-dimensional column tests. In addition, the influence of injection conditions on the flushing efficiency of saponin was also evaluated. The results show that the saponin with low COD and degradability performed the best removal efficiency of the selected eluents. The extraction rates of total Cr, Cr (VI), ammonia nitrogen, and COD increase with increasing saponin concentration. In the batch test, the extraction rates of total nitrogen were less than 40%, and it was not sensitive to the concentration. Saponin can simultaneously extract heavy metals (total Cr and Cr (VI)), total nitrogen, ammonia nitrogen, and organics from the contaminated soil. The leaching effect of saponin is obviously different under different injection modes. For contaminated soil dominated by total Cr or Cr (VI), continuous injection is recommended. If total nitrogen or ammonia nitrogen is the priority target, the step-gradient injection can demonstrate better removal efficiency. Muti-pulse injection is preferred when organics are the main factor in mixed contaminated soil. more...

A new apparatus and an interpretation method simplified from existing solutions of spherical air flow in soil were developed to measure in situ air permeability (ka) of unsaturated soil. By pumping air with a controlled volumetric flux (qv) into a spherical aeration bulb and measuring the corresponding pseudo-steady-state air gauge pressure (Δp0), ka was determined based on the slope of a qv–Δp0 relationship. The method was applied to measure ka in a full-scale landfill cover. The ka measurements were verified by finite-element modelling of air flow. The measurements show good agreement with the computed results. Sensitivity analyses reveal that using a smaller bulb radius (r0) would increase the measurement accuracy by minimising the boundary effects associated with atmospheric conditions and contrasting ka between neighbouring soils. Yet, the use of a small bulb would result in more prominent effects of preferential flow and hence substantial overestimation of ka. For a small bulb size (r0 = 0.01 m), the measurement accuracy of ka could be within 15% (i.e., 2.4 × 10−13 to 6.3 × 10−13 m2) of the true values when the ratio of vertical-to-horizontal ka is between 0.4 and 1. more...

The geosynthetic-encased vertical column and geosynthetic-embedded horizontal cushion are recognized as the effective methods to reduce the settlement of the soft subgrade. This paper investigated the settlement behavior of a soft subgrade reinforced by geogrid-encased stone column and geocell-embedded sand cushion using the finite element analysis method (Plaxis 2D). The simulating settlement was in good agreement with the field monitoring data, indicating the reasonability of the designed model and adopted parameters. After that, the factors, geocell layer in sand cushion, encasement length around stone column, and standing time between embankment filling stages, were employed to study their influences on the subgrade settlement. The results showed that the embedment of geocell reduced construction settlement, postconstruction settlement, and differential settlement is attributed to the increase in stiffness of sand cushion and therefore the uniform distribution of additional stress on subgrade surface. When the encasement length of stone column increased from 1D (one time the column diameter) to 8D (full encasement), the settlement in construction stage and postconstruction stage decreased by 32.2% and 35.1%, respectively, which is benefited from the increase in the compression modulus of the column. The maximum lateral deformation occurred at the position of about 2D from the top of the stone column, and it decreased more significantly when the encasement length increased from 1D to 4D than that from 4D to 8D. The encasement length up to 4D is found to be adequate in reducing the subgrade settlement and the column lateral deformation based on the consideration of performance and economy. The extension of the filling interval increased the construction settlement caused by soil consolidation, while it decreased the postconstruction settlement. more...

To limit the oxidation of waste rocks that originates from mining operations and the subsequent leaching of acidic solutions with high concentration of metal ions, a tailing–rock–clay triple layer capillary cover system was developed to prevent rainwater infiltration in humid climatic regions. The fine grained soil (FGS) layer consists of mine tailing and a hydrodesulfurization (HDS) clay from waste-water treatment with a 95:5 mass ratio. The coarse grained soil (CGS) layer consists of local waste rock granules with a size of 1–10 mm. Methyltrimethoxysilane (MTMS), an oxidation-inhibiting agent with strong hydrophobicity, was passivated on the rock grains to further reduce water infiltration and leaching of metal ions. Prototype-scale column tests were performed with matric suction and water content measurements under 680 min rainfall of 60 mm/h, the most severe annual precipitation case scenario for the Dexing Copper Mine (Jiangxi Province, China, 28.95° N, 117.57° E, humid climate). Both the uncoated and the coated covers exhibited zero leakage throughout the experiment. The passivation on rock granules in the coated cover increased the water entry value (WEV) of the CGS layer to −0.56 kPa. This led to a 15 mm water storage increment in the overlain FGS layer as compared to that in the uncoated cover, and induced lateral drainage (5% of the precipitation) in the FGS layer, which was not overserved in the uncoated cover. The concentrations of the leached Fe2+, Cu2+, Zn2+, Mn2+ and Mg2+ cations drained from the CGS layers of the uncoated cover were 0, 0.4, 0.8, 73.5, and 590.5 mg/L, which are all within the regulation limits of industrial discharge water standards. The concentrations of Cu2+, Mn2+ and Mg2+ cations drained from the coated CGS layer were reduced by 1–3 orders of magnitude. The abovementioned laboratory studies validated the water retention and leaching prevention abilities of the proposed three-layer capillary covers and the MTMS coating, which hold promises in engineering applications. more...

Landfill leachate contaminated groundwater is widespread all over the world. In order to study the organic contaminant removal efficiency of landfill leachate contaminated groundwater under oxygen micro-nano-bubble (MNB) aeration, a series of lab-scale experiments of oxygen MNB aeration as well as common bubble (CB) aeration were conducted. On the one hand, the difference of mass transfer, microbial activity enhancement and contaminant removal efficiency between MNB and CB aeration were estimated. On the other hand, the composition variations of dissolved organic matter (DOM) in groundwater treated by MNB or CB aeration were characterized by ultraviolet-visible (UV-VIS) absorption spectrum and fluorescence excitation-emission matrix (EEM). The test results showed that the oxygen utilization efficiency and volumetric oxygen transfer coefficient of MNB aeration were 10 and 50 times that of oxygen CB aeration, respectively. On the 30th day after MNB aeration, the dehydrogenase activity (DHA) of groundwater increased by 101.25%. Compared with CB aeration, the chemical oxygen demand (COD), 5-day biochemical oxygen demand (BOD5) and ammonia nitrogen removal efficiency under MNB aeration increased by 29.72%, 13.43% and 138.59%, respectively. With the biodegradation effect of MNB aeration, a large number of protein-like and soluble microbial by-product substances were degraded, and humic and fulvic acid-like substances were degraded to a certain level. Oxygen MNB aeration played a chemical oxidation effect while enhancing the biodegradation of groundwater, and it was an energy-efficient landfill leachate contaminated groundwater treatment method. more...

Disposal of the excess excavated soft soils produced in construction is a contemporary engineering challenge. A win-win solution could be found through utilising much excavated soil during reclamation of abandoned mines, and an evaluation model is necessary to realise this solution. This study aimed to propose a decision-making framework for large-scale disposal of excavated soft soil during mine reclamation using a Bayesian network (BN). Utilising multi-facet information, a decision-making path considering engineering and economic factors, and engineering risks was established. Thereafter, the practicability of backfilling much excavated soft soil into 215 abandoned opencast mines located in Wenzhou, China was evaluated. Based on the decision-making path and information of the 215 mines, a BN including 22 nodes was established with the practicability of large-scale soil disposal in mines as the decision node. Consequently, 40 valid mines were evaluated to be able to absorb 5 × 107 m3 soil, around 50% of the total excavated soil from the municipal districts of Wenzhou during 2020–2024. The BN evaluation showed high reliability with accuracy of all the nodes >70% and that of the decision node >90%. Five input nodes were identified to be high-impact for evaluation of the practicability and total fill volume. more...

To promote environmental protection and sustainability, the use of plants and recycled wastes in geotechnical construction such as landfill covers is recommended. A landfill cover field test was conducted at the Shenzhen Xiaping landfill site, located in a humid climatic region of China. The main objective was to validate the field performance of a novel vegetated three-layer landfill cover system using recycled construction waste without the need of geomembrane. Unsieved completely decomposed granite and coarsely crushed concrete was used for the top and intermediate layers while sieved completely decomposed granite was used as the lowest layer. One section was transplanted with Bermuda grass while the other section was left bare. To assess the landfill cover performance, pore-water pressure, volumetric water content, percolation, and atmospheric parameters were measured for a period of 13 months under natural climatic conditions. The cumulative rainfall depth was about 2950 mm over the entire monitoring period. During rainfall, the presence of grass led to lower pore-water pressure (or higher suction) and volumetric water content in the three-layer landfill cover system. At the end of monitoring, the cumulative percolation was about 27 and 20 mm for the bare and grass-covered landfill covers, respectively. It is evident that the vegetated three-layer landfill cover system using recycled concrete without geomembrane can be effective in minimizing percolation in humid climates. more...

Flow properties of soils can impact a wide range of geotechnical, agricultural, and geophysical processes. Few studies focus on the physical understanding of how pore characteristics can affect flow properties in soils. In this paper, pore network modeling is utilized to investigate intrinsic permeability, water pressure distributions, flow patterns, and critical flow paths in soils with pores varying in size, connectivity, and anisotropy. The results show that increased mean diameter, decreased standard deviation, and increased coordination number of the pores can lead to an increase in intrinsic permeability in soils. Non-uniform water pressure and flow rate distribution will more likely occur in soils with a larger pore size variability. A higher coordination number mitigates the pressure localization but slightly exacerbates non-uniform flow. With the increase in the coefficient of variation (COV) of pore diameters, the percolation path becomes more tortuous and carries more flow. When COV increases from 0 (homogeneous) to 1 (large pore size variability), the tortuosity increases from 1.00 to ∼1.71 and the flux carried by the percolation path in soils increases from 2.0% to 7.8%. Pronounced preferential flows may take place in soils with uniformly distributed pore sizes, in which the percolation path can carry as much as 9.2% of the total flux. The anisotropy in pore throat sizes also increases the flow tortuosity and the fraction of flux carried by the percolation path. The permeability anisotropy Kh/Kv increases linearly as the pore throat size anisotropy µdh/µdv increases logarithmically. These results provide insight for designing soil barriers for either uniform flows or exacerbated preferential flow for fast transport. more...

Settlement prediction of municipal solid waste (MSW) is a key issue in the design, construction, and post-closure development of landfills. As MSW is a highly heterogeneous material with compressible and degradable elements, the factors causing compression and settlement are complex. This paper explores the mechanisms and timescales for the settlement of land-filled MSW, and develops a rational taxonomy and framework of understanding. Conceptual models are reviewed and discussed, and the relative importance of different causes of settlement is assessed with reference to new, high quality, datasets and data from the literature. more...

The chemical and geotechnical properties of solidified/stabilized (s/s) municipal solid waste incineration (MSWI) fly ash are of prime importance for the design and operation of landfill sites. This study conducted field and laboratory tests to investigate aging effects on the chemical and geotechnical properties of s/s MSWI fly ash. Field investigations included borehole sampling and cone penetration tests (CPTs), and laboratory analyses included the measurement of the chemical, physical, hydrological, and mechanical properties of s/s fly ash with different fill ages. The results showed that: 1) Cl concentrations in landfill leachate were as high as 52,700 mg.L−1, which may present a technical challenge for leachate treatment; 2) specific gravity decreased with fill age, which was attributed to the leaching of metal elements from the s/s fly ash; 3) mean particle size decreased with fill age, resulting in an increase in the gravimetric moisture retention capacity (MRC) and a decrease in the saturated hydraulic conductivity; 4) gravimetric MRC was much higher than the initial moisture content, suggesting water absorption by s/s fly ash after landfilling; and 5) shear strength decreased with fill age, which was consistent with the CPTs results. To improve the design and operation of s/s MSWI fly ash landfill sites, the following suggestions are made: 1) the use of concentrated MSW landfill leachate in the s/s fly ash process should be avoided to reduce the concentrations of subsequent landfill leachate; 2) leachate generation could be further reduced by improving landfill operation practices and by taking advantage of the absorption capacity of s/s fly ash; and 3) the specific geotechnical parameters of s/s fly ash should be obtained prior to the design of landfill sites, and their aging effects should also be taken into consideration. more...

Pore characteristics play central roles in the transport of water and gas through granular soils, which is relevant to a wide range of geotechnical and geoenvironmental applications. In this study, a numerical procedure combining the discrete element method and pore network model is presented to relate the physically representative pore structure to the particle geometric features, and rapidly predict the macroscopic flow properties of granular assemblies. This numerical procedure is applied to investigate the effects of particle gradation and geometry on the pore characteristics and water retention curves of granular soils under isotropic compression. The results indicate that a larger uniformity coefficient (Cu) of particle diameters results in a lower porosity. The porosity first decreases and then increases as the aspect ratio (AR) of the particles increases from 1.00 to 2.50 and reaches the minimum at AR = 1.75. As Cu ranges from 1.00 to 2.16, the standard deviations and mean values of pore geometry and connectivity parameters, including pore and throat diameters, pore spacings, and coordination numbers, present linear correlations. The logarithm of air entry pressure decreases linearly with the increasing logarithm of mean pore diameter in response to the variations in both Cu and AR. A higher pore diameter variance induced by a smaller Cu produces a lower fitting parameter m in the van Genuchten equation for water retention curves. more...

The variation characteristics and influence factors of methane emission at Jiangchungou landfill, one of the largest landfill in China, has been investigated by a one-year field monitoring campaign during 2015-2016. The methane concentration above the landfill surface varied widely from negligible to 33,975 ppm. At least 75% of the methane concentration values of the sampling points are lower than the allowed limit (500 ppm). More than 95% of the high concentration zones (500 ppm) were located in the temporary cover area (TA). Several environmental factors were found to be related to the variation of the concentration values. A clear correlation was observed between barometric pressure and exceeding-standard areas with a correlation coefficient of -0.743 (p 0.1). The concentration values in the final cover area (FA) were about one order of magnitude lower than those observed in the TA due to the fact that rapid methane production rate happened in the first 180 days after the high kitchen content wastes were landfilled. The percentages of the measured concentration values exceeding 500 ppm near the gas collection wells in TA zone were 71.5% in November, 2015 and 55.7% in January, 2016 due to the leakage from the sides of gas collection wells. The average methane concentration values on the HDPE geomembrane was higher than those observed on the loess cover due to the fact that the geomembrane was relatively thin (0.5 mm) and can be easily damaged by the operation vehicles. Thicker geomembranes (1.5 mm) with a good construction quality control are expected to provide better performance at this site. more...

Aiming at the serious shortage of landfill storage capacity and the urgent need for simple dumps treatment in China, a method to realize the recycling of landfill storage capacity and the environmental treatment of simple dumps is proposed, which determines the stabilization degree of landfill by in-site full-section borehole sampling to test the degradation stabilization index of solid phase of waste, and uses the basically stabilized waste by excavation and screening. Waste samples were taken at different depths by drilling from the Tianziling Landfill (Phase I) which is the first generation sanitary landfill. The construction fractions, combustible fractions and fine fractions were obtained by manual screening, then the determination and analysis of the fine fraction content, particle size distribution, physicochemical characteristic parameters varied with depth were conducted. After that, the variation of fine fraction and contaminant content with the degradation stabilization index, which was proposed herein, were analysed. The feasibility of landfill mining was discussed in the end. The following conclusions were drawn obtained: when the degradation stabilization index, which was suitable to characterize the degree of biochemical degradation of landfilled waste, was over 0.83, the landfilled waste was almost stabilized, the values of electrical conductivity (EC) and chemical oxygen demand (COD) of the leaching solution became stable as well; while the content of heavy metals and organic matter in the fine fractions dissatisfied the requirements of standards. If the fine fractions were treated with re-landfilling, the reduction rate of the fresh waste collected in a mixing way could reach 83% after basically stabilizing through the process of landfilling and mining, therefore landfill mining can effectively realize the recycling of the storage capacity of sanitary landfills. more...

A catastrophic displacement of a waste dump occurred on December 20, 2015, in Guangming New District, Shenzhen, China. During this event, approximately 2.51 × 106 m3 of construction waste slid out of the dump site affecting approximately 0.38 km2, destroying 33 buildings and killing 77 people. This study tries to reconstruct the dump structure prior to the failure event, including evolution of dump geometry, geotechnical profile, hydrogeological conditions, and physical properties of fill materials. The dumpsite had been an abandoned quarry before receiving construction wastes beginning in February 2014. Within 22 months, 5.83 × 106 m3 of construction wastes, some of which had high water content, filled the dumpsite forming a 110-m-high loose fill. The dominant component of the fill was completely decomposed granite (CDG) excavated from the adjacent underground construction. The dumping operation at the site was characterized by rapid filling, inadequate compaction and poor water drainage. Poor compaction on the fill materials resulted in low compactness. The measurements of soil density showed that over 80% of the collected CDG samples had a relative density (Dr) from 4% to 67%. The dynamic penetration tests conducted on the landslide bed indicated that the fill materials were loose to slightly dense at most of the penetration depth. No effective drainage facilities were provided at the dump site. A large quantity of water from a catchment area of 0.51 km2 readily poured into the dump, resulting in a significant rise in the phreatic surface. The rapid filling rate of 5–7 m/month was very likely to have caused a build-up of excessive pore-water pressure in the lower poorly drained fill, which was verified by borehole exposure of the confined groundwater and the evaluation of consolidation degree based on the measurements of soil density. The fill materials within the landslide bed were found to have a consolidation degree of 33% on average. A deep-seated translational failure occurred on the lower poorly consolidated fill layer, forming a very-fast-moving flow slide. more...

Special hydrogeological properties of granite regions control leachate migration in municipal solid waste (MSW) unlined landfills there. This study aimed to investigate leachate migration at an unlined landfill located in a granite region and explore an in-situ borehole groundwater TDS-profile method (BGTM) for identifying vertical distribution of leachate plume at landfill sites in granite regions. On basis of detailed site investigation using multiple methods (e.g., borehole investigation, water quality monitoring, and rock packer tests), hydrogeological model of the surveyed MSW landfill was established, and horizontal distribution of four contaminants including chemical oxygen demand, ammoniacal nitrogen showed that leachate plume could reach over 200 m away from downstream boundary of the source landfill. BGTM was demonstrated to be able to identify boundary of leachate plume under a field average influx >1.0 × 10−7 cm/s and a hydraulic conductivity of the evaluated layers >5.0 × 10−5 cm/s. Based on the site investigation, granite joints were found to be the major leachate migration channels in the lateral slope of the granite valley, and highly permeable layers such as alluvium were identified as the major leachate migration channels in the valley outlet. Meanwhile, a two-piece function was fitted between groundwater total dissolved solid (TDS) and electrical conductivity (EC) in the landfill site, and EC = 500 μS/cm was the limit between the two intervals. more...

New types of synthetic municipal solid wastes (MSWs) were developed, exhibiting engineering characteristics similar to those of real MSWs at different states of degradation in terms of total unit weight, void ratio, water content, compressibility, permeability, stress–strain relationship, and shear strength. Using these synthetic MSWs, several centrifuge model tests on the stability of geosynthetics-lined landfills with rising water levels were performed. The test results revealed the developing processes of MSW landfill failures induced by rising water levels. In most tests, a continuous slide occurred once a critical water level was attained. The ratio of critical water level and landfill height was 0.75–0.92 for present model tests using fresh or partly degraded synthetic MSWs with landfill slope ratio of 1:1–1:3, increasing with the increases of MSW degradation states and decreases of the slope ratio. An engineered berm increased the critical water level by 1.3%–9.5%. The landfills without an engineered berm tended to slide along the bottom liner; however, for normal landfills with an engineered berm and a slope ratio of 1:3, penetrating cracks developed when the failures occurred. These results provide a good reference for water level and stability control of the landfill, and the construction of an engineered berm is suggested to improve the stability of these landfills. more...

A 30 m long × 20 m wide capillary barrier cover (CBC) test site was constructed at the Jiangcungou landfill in Xi’an, China. The cover consisted of a compacted loess layer with a thickness of 0.9 m underlain by a gravel layer. After the cover surface was kept bare and exposed to natural climate conditions for nearly 5 months, one artificial rainfall event was implemented at the site. Vegetation was established at the test site after the first rainfall event. Four months later, a second artificial rainfall event was applied to the surface of the vegetated site. The pore-water pressures (PWPs) and volumetric water contents (VWCs) of the cover were monitored using jet-filled tensiometers and time-domain reflectometry moisture probes, respectively. Surface runoff and percolation were measured using field collection devices. The field measurements demonstrated a more rapid response of PWPs to the rainfall compared to the response of the VWCs. Percolation was observed when the PWPs near the interface reached the water-entry value of the gravel at local points. At that moment, the measured VWC near the interface was less than the VWC according to the water-entry value. The observation indicated that preferential flows took place in the compacted loess during the rainfall. As a result, the maximum water storage capacity was not reached at the onset of percolation. When percolation ceased, the average PWP near the interface decreased below the water-entry value, while the VWC near the interface was higher than that at the onset of percolation. Water storage at the completion of percolation was approximately 5% greater than that at the onset of percolation. Compared with the monolithic loess cover, the loess–gravel CBC increased the available water storage capacity by 41% at the completion of percolation. Vegetation had an insignificant influence on water storage capacity. more...

This paper presents failure probability assessment and parameter sensitivity analysis of a contaminant’s transit time through a compacted clay liner. Monte Carlo simulation (MCS) was used to assess failure probability, and the failure samples generated in the MCS were used to investigate the sensitivity of various uncertain parameters to the failure probability. To facilitate the MCS, a database on various transport parameters was developed by collecting and analyzing measurement data reported in literature. Failure probability assessment and parameter sensitivity analysis showed that the uncertainties in adsorption parameters, longitudinal dispersivity, and hydraulic conductivity have the most significant effects on failure probability. more...

The rapid development of urbanization in China has generated large amounts of municipal solid waste (MSW), which can contribute to certain dangers in landfills, such as liner ruptures, heap landslides, and landfill gas explosions. Therefore, a comprehensive and coupled model is necessary for landfill design and verification. In this study, a thermo-hydro-mechanical-biochemical (THMBC) coupled model is proposed, which considers biological degradation, skeleton deformation, particle compressibility, intra-particle water release, two-phase flow, pore water evaporation and condensation, and heat and solute transport. In the model, biochemical reaction rates are utilized to link the fluid source terms with the solid-mass loss, and to link the heat transport with biochemical reactions and other processes. Two cases were studied and utilized to verify the applicability of the proposed model in homeothermic and high-temperature (40 °C) circumstances via OpenGeoSys software and the ZJU Calculator, and the results of both case studies were found to agree with the measured experimental data. In general, this work provides a basic framework for the simulation of THMBC coupling in landfills. In future research, this framework can be improved by implementing more alternative constitutive equations in a single process. more...

Soil-bentonite slurry-trench cutoff walls using backfill consisting on-site sandy or silty soil and bentonite are extensively used as engineered barriers for the containment of groundwater and soil pollution. Chinese loess has been shown to have large adsorption capacity regarding heavy metals. There is a great potential to use Chinese loess as amendments to improve the adsorption capacity of the wall. Batch and column tests were carried out to investigate the adsorption and transport of Pb(II) in loess modified soil-bentonite (LSB). Batch tests were conducted to study the effects of contact time, initial Pb(II) concentration, loess proportion in LSB, and pH on Pb(II) adsorption. The rate constant of pseudo-second-order kinetic adsorption model of LSB is two times greater than that of soil-bentonite (SB), which indicates that the adsorption rate of LSB is much faster than that of SB. The mean free energy of adsorption evaluated by D-R model is 15.56 kJ/mol and 18.89 kJ/mol for SB and LSB, respectively. This indicates the adsorption mechanisms of SB and LSB are mainly ion exchange and chemical reaction. The adsorption capacity of LSB increases linearly with the increase of the loess amount in LSB. The maximum adsorption amount of LSB containing 20% loess can be 2 times greater than that of SB. Results also indicate that Pb(II) is first adsorbed onto loess until the adsorption amount Pb(II) onto loess reaches its adsorption maximum. An equation considering this effect was proposed for prediction of the adsorption capacity of LSB. A set of column tests were carried out to evaluate the tortuosity, mechanical dispersion and retardation factor regarding lead transport in SB and LSB vertical engineered barrier. The retardation factor of LSB and SB are determined to be 38 and 15, respectively, by the column tests. The Kd values obtained from batch tests are significantly larger than those obtained from column tests due to the difference of soil-water ratio used for these two types of tests. Using the obtained parameter values, the breakthrough time of Pb(II) through LSB wall is evaluated to be about 2 times greater than that of the SB wall when the hydraulic head difference is more...

The water vapor diffusion can be enhanced by the heating from municipal solid waste, and significantly impact the evaporation process in the earthen final cover. The parameters associated with the water vapor diffusion are usually measured by using the instantaneous profile method. This method is very time-consuming because the drying process lasts a long time. In this study, a bottom heating method is proposed to accelerate the drying process in a loess soil column. A constant temperature of 70 °C is applied at the bottom of the soil column. The thermo-hydraulic response of the loess is monitored along the soil column. A numerical model is developed to simulate the coupled thermo-hydraulic process. The numerical model is used to back analyze the tortuosity τ of the loess for vapor diffusion and the parameter a of an empirical evaporation function. We found that the bottom heating accelerated the drying process of the soil column by almost 22 d compared with the conditions without heating under the same evaporation boundary. Before Day 15, the proportions of the enhanced vapor flux in the total water loss were higher than 50%, dominating the evaporation process. The experimental and numerical study demonstrated that the proposed heating method is able to obtain the parameters of vapor diffusion more efficiently than the conventional method. more...

The use of loess as an earthen final cover material is promising in northwest China which has an arid and semi-arid climate. A full-scale testing facility with an area 30 m long by 20 m wide was constructed at the Xi’an landfill of municipal solid wastes to investigate the performance of an inclined capillary barrier cover. The cover consisted of a compacted loess layer underlain by a gravel layer. The testing facility was well instrumented for a gas permeation test and recording of the soil conditions in terms of volumetric water content, pore gas pressure, and soil temperature. Tests were performed to measure the gas permeability of the compacted loess before and after the planting of vegetation on the cover. The field measurements demonstrate that the capillary break at the fine/coarse soil interface allows the upper compacted loess layer to retain more water, and conversely reduces its gas permeability, which is favorable for reducing landfill gas emissions. When the degree of saturation of the compacted loess was greater than 85%, the gas permeability decreased significantly with a further increment in volumetric water content. The growth of vegetation roots tended to fill the large pores in the upper loosely-compacted loess, resulting in a decrease in gas permeability of one order of magnitude. The influence of soil clods in the compacted loess on gas permeability can be one to two orders of magnitude due to an increase in pore size and a decrease in tortuosity. more...

Engineering properties of municipal solid waste (MSW) depend largely on the waste's initial composition and degree of degradation. MSWs in developing countries usually have a high kitchen waste content (called HKWC MSW). After comparing and analyzing the laboratory and field test results of physical composition, hydraulic properties, gas generation and gas permeability, and mechanical properties for HKWC MSW and low kitchen waste content MSW (called LKWC MSW), the following findings were obtained: (1) HKWC MSW has a higher initial water content (IWC) than LKWC MSW, but the field capacities of decomposed HKWC and LKWC MSWs are similar; (2) the hydraulic conductivity and gas permeability for HKWC MSW are both an order of magnitude smaller than those for LKWC MSW; (3) compared with LKWC MSW, HKWC MSW has a higher landfill gas (LFG) generation rate but a shorter duration and a lower potential capacity; (4) the primary compression feature for decomposed HKWC MSW is similar to that of decomposed LKWC MSW, but the compression induced by degradation of HKWC MSW is greater than that of LKWC MSW; and (5) the shear strength of HKWC MSW changes significantly with time and strain. Based on the differences of engineering properties between these two kinds of MSWs, the geo-environmental issues in HKWC MSW landfills were analyzed, including high leachate production, high leachate mounds, low LFG collection efficiency, large settlement and slope stability problem, and corresponding advice for the management and design of HKWC MSW landfills was recommended. more...