Search

The methane emission in a loess-gravel capillary barrier cover (CBC) in winter and summer was investigated by constructing a full-scale testing facility (20 m × 30 m) with a slope angle of 14.5° at a landfill in Xi’an, China. Weather conditions, methane emission, gas concentration, temperature, and volumetric water content (VWC) in the CBC were measured. The temperature and moisture in the CBC showed a typical seasonal pattern of warm and dry in summer and cold and wet in winter. Accordingly, the maximum methane oxidation rate and methane emission were higher in summer. The mean methane influx and methane emission decreased significantly as the VWC increased beyond 40% (i.e., a degree of saturation 0.85) at a depth of 0.85 m, which was near the loess/gravel interface. At this depth, more water was presented in the loess layer in the downslope direction due to capillary barrier effects, which increased the upslope methane emission. More dominant methane emission in the middle- and upper-section of the CBC occurred in summer than in winter as there was less soil moisture to facilitate methane transfer. The LFG balance showed that a significant fraction of the loaded LFG was not accounted in the flux chamber measurements due to the preferential flow along the edges of the CBC. The maximum methane oxidation rate was 93.3 g CH4 m−2 d−1, indicating the loess-gravel CBC could mitigate methane emissions after landfill closure.

In this paper, three sets of laboratory tests were conducted on high-food-waste-content (HFWC-), no-food-waste-content (NFWC-) and decomposed (D-) MSWs to characterize their compression behaviors. The immediate compression ratios C'c were 0.30, 0.23 and 0.18 for HFWC-MSW, NFWC-MSW and D-MSW respectively, and tended to increase with the increasing food waste content of MSW. The release of intra-particle water contained in food waste contributed over 23.6-29.2% to immediate compression for HFWC-MSW. The mechanical creep ratios C'sc were 0.02, 0.015 and 0.01 for HFWC-MSW, NFWC-MSW and D-MSW respectively. A prediction model for C'sc was proposed which incorporated the effects of moisture content, dry unit weight and organic waste content. The bio-compression ratios C'sbI, C'sbII and C'sbIII in response to degradation stage I, II and III were 0.12, 0.10 and 0.02 for HFWC-MSW, and were 0.01, 0.15 and 0.01 for NFWC-MSW. Bio-compression is dominant in stage I and II and mechanical creep is the major contributor in stage III for HFWC-MSW, but to NFWC-MSW, mechanical creep is dominant in stage I and III, and bio-compression takes the main position in stage II. The bio-compression tended to increase linearly with leachate draining rate for HFWC-MSW, and the release of intra-particle water contributed 61.9-65.6% to bio-compression. A new model was proposed that can well capture the highly non-linear behavior of bio-compression for both HFWC-MSW and NFWC-MSW. Based on the above findings, the settlement behavior of HFWC-MSW and NFWC-MSW landfills was compared, and suggestions for technique-efficient and cost-effective design of a NFWC-MSW landfill were discussed.

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.

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.

Microbial aerobic methane oxidation (MAMO) has been considered as an environmental-friendly method for mitigating methane emission from municipal landfill sites. Soil column has in a landfill cover under one-dimensional (1-D) condition. However, most of the published soil column tests failed to simulate 1-D heat transfer due to the use of thermal conductive boundary at the sidewall. In the present study, a heavily instrumented soil column was developed to quantify the effects of thermal boundary condition on the methane oxidation efficiency under different ambient temperatures in landfill cover soil. The sidewall of the soil column was thermally insulated to ensure 1-D heat transport as would have been typically expected in the field condition. Two soil column tests with and without thermal insulation were conducted at a range of controlled ambient temperatures from 15 to 30°C, for studying how soil moisture, matric suction, gas pressure, soil temperature and gas concentration evolve with MAMO. The test results reveal that ignoring thermal insulation in a soil column test would result in a greater loss of soil heat generation by MAMO and hence oxidation efficiency by up to 100% for the range of temperature considered. When the ambient temperature increased to 30°C (but less than the optimum temperature for MAMO), the MAMO efficiency increased abruptly at first but then decreased substantially with time, and this is likely due to the accumulation of biomass generated by MAMO.

Gaseous emissions from municipal solid waste (MSW) disposal plants pose serious odor pollution and health risks. In this study, the emission of volatile organic compounds and carbon disulfide was compared in the main processing units of three disposal methods, i.e., landfilling, eco-mechanical biological treatment (EMBT) and anaerobic fermentation in a MSW disposal plant. Among the detected volatile compounds (VCs), the top ten odor compounds were methanethiol, dimethyl sulfide, dimethyl disulfide, carbon disulfide, styrene, m-xylene, 4-ethyltoluene, ethylbenzene, 2-hexyl ketone and n-hexane in the MSW disposal plant. Sulfur compounds were the main source of odor at the majority of sampling sites, and aromatic compounds were the dominant odor substrates at the tipping unit and sorting system of EMBT, while 2-hexanone was the major odor substrate at the tipping unit (AT) and sorting system (AS) of anaerobic fermentation and the landfill working surface. At AS and AT, the lifetime cancer risk values for 1,2-dichloroethane and trichloroethylene exceeded the carcinogenic risk value (>1.0E-04), and the hazard index values of naphthalene, trichloroethylene and acrolein all exceeded the acceptable level (>1). Therefore, special attention should be paid to VC emissions from MSW disposal facilities, and protection measures should be adopted for on-site workers to minimize health risks.

Previous investigations using time domain reflectometry (TDR) to detect ionic contaminants has mainly focused on saturated coarse-grained soils and conventional probes (e.g., coaxial, two- or three-rod probe). To explore the applicability of using the TDR penetrometer for the site investigation of ionically contaminated land, a theoretical framework was proposed to estimate the pore water electrical conductivity of both saturated and unsaturated silts based on measured soil dielectric permittivity and bulk electrical conductivity. The theoretical framework consists of three equations, the empirical equation relating soil dielectric permittivity and volumetric water content, the soil dielectric mixing model, and the modified Archie’s law considering the surface conductivity. To verify the theoretical framework, chamber tests using the TDR penetrometer were performed to detect CuSO4 contaminants in silt columns. Results show that the theoretical framework provides an increasingly better calculation of the pore water electrical conductivity of saturated and unsaturated silt with increasing the concentration of CuSO4 solution. This is because that the modified Archie’s law with a constant surface conductivity in the theoretical framework can well capture the relationship between soil bulk electrical conductivity and pore water electrical conductivity at high solution concentrations (i.e., 0.015 and 0.030 mol/L CuSO4 solutions), but not at low solution concentrations (i.e., tap water). The theoretical framework and chamber tests are expected to provide scientific guidance for extending the capacity of TDR penetrometer to the site investigation of ionically contaminated land.

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.

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.

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.

The high food waste content (HFWC) MSW at a landfill has the characteristics of rapid hydrolysis process, large leachate production rate and fast gas generation. The liquid-gas interactions at HFWC-MSW landfills are prominent and complex, and still remain significant challenges. This paper focuses on the liquid-gas interactions of HFWC-MSW observed from a large-scale bioreactor landfill experiment (5m×5m×7.5m). Based on the connected and quantitative analyses on the experimental observations, the following findings were obtained: (1) The high leachate level observed at Chinese landfills was attributed to the combined contribution from the great quantity of self-released leachate, waste compression and gas entrapped underwater. The contribution from gas entrapped underwater was estimated to be 21-28% of the total leachate level. (2) The gas entrapped underwater resulted in a reduction of hydraulic conductivity, decreasing by one order with an increase in gas content from 13% to 21%. (3) The "breakthrough value" in the gas accumulation zone was up to 11kPa greater than the pore liquid pressure. The increase of the breakthrough value was associated with the decrease of void porosity induced by surcharge loading. (4) The self-released leachate from HFWC-MSW was estimated to contribute to over 30% of the leachate production at landfills in Southern China. The drainage of leachate with a high organic loading in the rapid hydrolysis stage would lead to a loss of landfill gas (LFG) potential of 13%. Based on the above findings, an improved method considering the quantity of self-released leachate was proposed for the prediction of leachate production at HFWC-MSW landfills. In addition, a three-dimensional drainage system was proposed to drawdown the high leachate level and hence to improve the slope stability of a landfill, reduce the hydraulic head on a bottom liner and increase the collection efficiency for LFG.

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.

A large-scale bioreactor experiment lasting for 2 years was presented in this paper to investigate the biochemical, hydrological and mechanical behaviors of high food waste content (HFWC) MSW. The experimental cell was 5 m in length, 5 m in width and 7.5 m in depth, filled with unprocessed HFWC-MSWs of 91.3 tons. In the experiment, a surcharge loading of 33.4 kPa was applied on waste surface, mature leachate refilling and warm leachate recirculation were performed to improve the degradation process. In this paper, the measurements of leachate quantity, leachate level, leachate biochemistry, gas composition, waste temperature, earth pressure and waste settlement were presented, and the following observations were made: (1) 26.8 m 3 leachate collected from the 91.3 tons HFWC-MSW within the first two months, being 96% of the total amount collected in one year. (2) The leachate level was 88% of the waste thickness after waste filling in a close system, and reached to over 100% after a surcharge loading of 33.4 kPa. (3) The self-weight effective stress of waste was observed to be close to zero under the condition of high leachate mound. Leachate drawdown led to a gain of self-weight effective stress. (4) A rapid development of waste settlement took place within the first two months, with compression strains of 0.38–0.47, being over 95% of the strain recorded in one year. The compression strain tended to increase linearly with an increase of leachate draining rate during that two months.

A newly developed static chamber method with a laser methane detector and a biogas analyser was proposed to measure the landfill gas emissions and methane (CH4) oxidation rates in landfill covers. The method relied on a laser methane detector for measuring CH4 concentration, avoiding gas samplings during test and hence the potential interference of gas compositions inside the chamber. All the measurements could be obtained on site. The method was applied to determine the landfill gas emissions and CH4 oxidation rates in a full-scale loess gravel capillary barrier cover constructed in landfill. Both laboratory calibration and in-situ tests demonstrated that fast (i.e. 4 oxidation rates in landfill site.

Loess is widely distributed in Northwest China where the rainy season coincides with the warm and vegetation growth period. The use of loess as a capillary barrier cover (CBC) material is promising. However, how the loess/gravel CBC perform as a capillary barrier and landfill gas emissions controller remains elusive. In this study, the performance of a designed CBC comprised 1.3 m-thick compacted loess underlain by 0.3 m-thick gravel in extremely wet and dry years of Xi'an city from 1950 to 2000 was analyzed using numerical modeling. An instrumented CBC test section comprised 0.9 m-thick compacted loess underlain by 0.3 m-thick gravel was constructed to show the hydraulic responses in real conditions from January 2015 to January 2017. The numerical results indicated that the designed CBC performed well as a capillary barrier as no percolation occurred during the extremely wet periods. Despite adopting a CBC of 0.4 m thinner than the designed one, the test section produced only 16.16 mm percolation during the two-year monitoring period, and that can meet the recommended limit of 30 mm/yr. The effect of the capillary break on increasing the water storage within the CBC was observed at the test section in fall. The increased water storage can significantly decrease the gas permeability, and thus improve the performance of the CBC as a LFG emissions controller. Furthermore, the LFG emissions can be controlled to meet the limit set by the Australian guideline by decreasing the bottom gas pressure and artificial watering. Finally, a procedure was proposed to enhance the performance of CBCs.

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.

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

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.

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.

In this study, integrate electrical resistivity tomography (ERT) tests were carried out in a large-scale (5.0 × 4.0 × 7.5 m) MSW landfill cell to investigate the possibility of detecting perched leachate mounds, leachate level, and gas accumulation zones at wet landfills. The resistivity of both bulk waste and waste components at different moisture states were measured and the three-phase volumetric relationships of the waste pile were analyzed to better interpret the ERT test results in the large-scale cell. The following observations were given: (1) The relationship between resistivity and volumetric moisture content (VMC) of waste sample can be reasonably fitted by Archie's law. The resistivity of waste components at a saturated state was all lower than 21 Ω m. (2) A significant amount of void gas was entrapped in the underwater waste, being 30.4-34.8% of the whole waste pile in volume. (3) Low-resistivity zones ( 5.0 Ω m) were observed in the waste pile being fully drained under a gravity condition, which was believed to be related to a perched leachate. (4) The average VMC values of the waste layer below and above the leachate level were in the ranges of 46.5-53.1% and 28.1-41.3%, respectively. (5) Irregular variations of high-resistivity zones ( 40 Ω m) observed in the underwater waste were associated with the accumulation and dissipation of gas pressure. It was found that the "gas-breaking value" in the gas accumulation zone was up to 10.5 kPa greater than the pore liquid pressure in the stable methanogenesis stage. These findings shone a light on the possibility of using the ERT method as an efficient tool for mapping the gas/leachate distribution and improving operations at wet landfills.

Devastating landslides were frequently triggered by earthquakes and caused severe damage and human losses. More than 25,000 people were killed by the Wenchuan earthquake-induced landslides. A proper model for estimating loss of lives is important in quantifying the human risks posed by earthquake-induced landslides. This paper presents a new model for quantitatively estimating the human vulnerability to earthquake-induced landslides using Bayesian networks. A database incorporating information of fatal landslides induced by the Wenchuan earthquake is established. A Bayesian network is constructed according to a logic structure of loss-of-life mechanisms by considering four types of key factors, i.e., deposit thickness, building damage, evacuation, and resistance capacity. The probabilities of the nodes (factors) and the arcs (inter-relationships) of the network are quantified according to statistical data, judgment based on experiences, and existing physical or empirical models. The human vulnerability to earthquake-induced landslides is quantitatively estimated through constructing a systematic structure considering the uncertainties of the control factors and their inter-relationships. Comparison between the recorded fatality rate and predicted fatality is conducted to verify the proposed model. Finally, sensitivity analysis is conducted to identify the most important parameters that lead to loss of lives.

The stabilization behavior of landfilled municipal solid waste (MSW) plays an important role in the design, operation, and after care of landfills. The stabilization is dependent on the biological degradation and consolidation processes of landfilled MSW. A degradation–consolidation model for MSW was developed, which took biological degradation, skeleton deformation, two-phase flow, and solutes transport into consideration. In this model, the mass transformations of solid to liquid and then to gas were involved. The compression, hydraulic and solute transport material properties were related to the solid mass loss and the pore volume change. Indicators for the stabilization behavior of landfilled MSW were proposed. These indicators were calculated using the degradation–consolidation model to compare the stabilization behavior of landfilled high food waste content (HFWC) and low food waste content (LFWC) MSW. The results showed that the stabilization process of HFWC MSW landfills could be divided into rapid degradation, slow degradation, and post-stabilization stages based on the development of stabilization indicators. The normalized ratio of cellulose to lignin could be implemented to assess the stabilization stage of landfill more easily in practice.

Transient evaporation method is promising for rapid measurement of soil water retention curve (WRC). Existing apparatuses of transient evaporation method are not ideal for measuring the WRC of structured soils because of the sample disturbance induced by invasive water content probes used. In this study, non-invasive TDR probes with different waveguide layouts (i.e., different number of conductors and waveguide length) were developed to measure the WRC of loess during transient evaporation, while the soil suction is recorded through a tensiometer. Results show that the WRCs of undisturbed and remolded loess measured by a three-conductor non-invasive TDR probe are in good agreement with the results of pressure plate tests. The differences in the air entry value (AEV) and desorption rate between the WRCs measured by the transient evaporation method and the pressure plate measurement are less than 10 %. On the other hand, the WRCs measured by a two-conductor non-invasive TDR probe underestimate the water content for a given suction. The AEV of undisturbed and remolded loess determined by the transient evaporation method is 66.7 % and 112.9 % smaller than the results of pressure plate measurements, respectively. The underestimation of the two-conductor non-invasive TDR probe in measuring the WRC of loess can be attributed to the fact that the vertical sampling range of two-conductor non-invasive TDR probe is two times greater than that of the tensiometer. The results in this study show the effectiveness of using the non-invasive TDR probe along with a tensiometer for measuring the WRC. More importantly, great caution should be taken on compliant sampling volume of the non-invasive TDR probe and tensiometer to obtain accurate WRC measurements.

For degradable porous media (DPM) experiencing solid particle or mass loss, the volume change process is complex. To investigate the pore water pressure response and associated deformation during the consolidation process of saturated DPM theoretically, the generalized governing equation for one-dimensional (1-D) consolidation of saturated DPM was proposed. Then, saturated municipal solid waste (MSW) was taken as an example. The generalized and simplified 1-D consolidation models were established for saturated MSW, respectively. Analytical solution to the simplified 1-D consolidation model considering degradation-dependent compressibility only was derived for saturated MSW. Based on this analytical solution, case studies were carried out. Excess pore water pressure (u sw) being larger than the initial value was found in deeper waste during the early stage of consolidation under a constant surcharge load. This is because the loading effect resulted by the increase of compressibility is greater than the unloading effect resulted by the increase of void space. An increase of degradation rate coefficient c could result in greater loading effect, and hence causes increasing u sw in waste. The numerical results are of wider interest, being applicable to other DPM.

In June 2008, the Shenzhen landfill slope failed. This case is used as an example to study the deformation characteristics and failure mode of a slope induced by high water levels. An integrated monitoring system, including water level gauges, electronic total stations, and inclinometers, was used to monitor the slope failure process. The field measurements suggest that the landfill landslide was caused by a deep slip along the weak interface of the composite liner system at the base of the landfill. The high water level is considered to be the main factor that caused this failure. To calculate the relative interface shear displacements in the geosynthetic multilayer liner system, a series of numerical direct shear tests were carried out. Based on the numerical results, the composite lining system simplified and the centrifuge modeling technique was used to quantitatively evaluate the effect of water levels on landfill instability.