Model For Municipal Solid Waste Research Articles

Modeling the mechanical behaviour of fibre reinforced sands

ABSTRACT The mechanical behaviour of Fibre-reinforced sands (FRS) has been extensively studied, presenting improved mechanical properties compared to unreinforced soils. Many models have been developed to predict its general stress-strain behaviour. However, the use of double-phase models in FRS is still incipient. Double-phase models are advantageous because they can simulate the whole FRS and the behaviour of its individual components, soil skeleton and reinforcement. This paper uses a modified model for Municipal Solid Waste to reproduce the FRS mechanical response. Introducing a new hardening parameter and a dilatant zone allowed the model to reproduce FRS dilatancy. The model’s variables are easily understood, allowing the reproduction of the mechanical behaviour of FRS formed by sands with void ratios ranging from 0.610 to 0.917 and mean grain size from 0.29 to 0.83 mm. The fibres’ lengths varied from 12.5 to 51 mm. The results of triaxial and hollow cylinder torsional tests under different stress paths had their main characteristics (peak strength, post-peak behaviour, dilatancy and reinforcement effectiveness) well captured by the model. Predicted and experimental FRS’s deviator stress usually differ by less than 15% and the model performance is equivalent or superior to other available models, even requiring fewer input parameters.

Study of Modified Primary Compression Index Tests and a Regression Model for Municipal Solid Waste Considering the Temperature Effect

The modified primary compression index (MPCI) of municipal solid waste (MSW) is an important parameter for describing the primary consolidation settlement of MSW. It is beneficial to calculate the settlement and storage capacity of landfills accurately by calculating the MPCI of MSW correctly. This article studies the primary consolidation compression characteristics and influencing factors of MSW through a consolidation experiment considering temperature control. The experimental results show that the MPCI increases with an increase in temperature, decreases with an increase in dry weight, increases with an increase in water content, and increases with an increase in organic matter content. According to the above findings, an MPCI regression fitting model was established. The reliability and accuracy of the model was validated by the experimental results of the indoor bioreactor test considering temperature control.

An elastoplastic constitutive model for municipal solid waste (MSW) incorporating solid particle compression and fibrous reinforcing effect

The failures in municipal solid waste (MSW) landfills could result in considerable ecological as well as social problems. Numerical simulations are widely employed to analyze MSW deformation and stability. These methods require an appropriate stress-strain characterization of MSW, which is crucial. Different from soils, the extremely complicated constituents of MSW contain a large number of fibrous reinforced and particle compressible materials. The findings of numerous tests suggest that the fiber reinforced phase and the basic phase are solely responsible for determining the mechanical properties of MSW. On the basis of the double-phase assumption, a new plastic potential function of MSW is developed considering that the reinforcement of fibrous materials only relates to plastic shear strain and the particle compression only affects plastic volumetric strain. According to the associate flow rule, a constitutive model based on elastoplasticity is developed for MSW. The strain hardening behaviour of MSW is well predicted by the model, and this behaviour is in good agreement with experimental evidence. Effects of confining pressure and fibre content are modelled, together with the mechanical and deformation behaviour of MSW. The accurate calculation of effective stresses is obtained through considering the MSW particle compression under the undrained conditions. Parametric investigations calibrate the model and show its properties by comparing them to data from triaxial tests. Moreover, incorporating the proposed model, finite-element numerical simulation was conducted, and the results of finite-element numerical simulation were compared with field monitoring results.

A double-phase constitutive model for municipal solid waste with a fiber pullout criterion to evaluate the softening behavior

Flowslide disasters of municipal solid waste (MSW) landfills generally have a long flow distance. In the condition of extremely large deformation, the strength of MSW cannot be reinforced by embedded fibers (also called hardening) with fiber pullout. To describe this softening behavior of MSW in a state of large strain, this study proposes a double-phase constitutive model with a fiber pullout criterion. The mechanical response of MSW is attributed to the basic phase and the fibrous phase described by the modified Cam-Clay (MCC) model with an extension and a pressure-dependent elastic model, respectively. The fiber pullout criterion is governed by the shear stress acting on the fiber-particle interface and the stress state of the fibrous phase. The compressibility of MSW particles is also considered to well reproduce the variations of effective stress in undrained conditions. The model is verified with the previous triaxial tests in drained and undrained conditions, and the mechanism of MSW softening behavior is revealed through a parametric study. Results show that the fiber pullout occurs before the strength of MSW reaches its peak and the stress state remains stable when all fibers are pulled out.

Numerical study of strain development in high-density polyethylene geomembrane liner system in landfills using a new constitutive model for municipal solid waste

Tensile strain development in high-density polyethylene (HDPE) geomembrane (GMB) liner systems in landfills was numerically investigated. A new constitutive model for municipal solid waste (MSW) that incorporates both mechanical creep and biodegradation was employed in the analyses. The MSW constitutive model is a Cam-Clay type of plasticity model and was implemented in the finite difference computer program FLAC™. The influence of the friction angle of the liner system interfaces, the biodegradation of MSW, and the MSW filling rate on tensile strains were investigated. Several design alternatives to reduce the maximum tensile strain under both short- and long-term waste settlement were evaluated. Results of the analyses indicate that landfill geometry, interface friction angles, and short- and long-term waste settlement are key factors in the development of tensile strains. The results show that long-term waste settlement can induce additional tensile strains after waste placement is complete. Using a HDPE GMB with a friction angle on its upper interface that is lower than the friction angle on the underlying interface, increasing the number of benches, and reducing the slope inclination are shown to mitigate the maximum tensile strain caused by waste placement and waste settlement.

A constitutive model for municipal solid waste considering mechanical creep and biodegradation-induced compression

A constitutive model is developed to describe the stress–strain–time behavior for decomposing municipal solid waste (MSW) within a critical state soil mechanics framework. The model is an extension of the Modified Cam-Clay plasticity model. In this model, three sources contribute to the hardening of MSW due to volumetric strain: time-independent plastic volumetric strain, time-dependent volumetric mechanical creep strain, and time-dependent volumetric strain due to the biodegradation (decomposition) of MSW. The MSW model was evaluated through numerical analyses of large-scale one-dimensional compression tests in the laboratory and the field and the reported vertical and horizontal deformations of a MSW landfill. The associated model parameters were obtained by compositional analysis of the waste, from values reported in the literature, and by fitting numerical results to observed behavior. For the laboratory compression test, the best-fit numerical simulation over-predicted the early settlement but converged on the experimental values after 200 days. Initially, the calculated vertical strains in the field-scale test deviated from the measured strains by up to 10% over the 398-day period of the test. However, numerical results after adjusting model parameters to provide the best fit with the measured strains resulted in a maximum deviation of less than 3% over the test duration. The calculated vertical displacements of the MSW landfill were consistent with field measurements. However, the calculated horizontal displacements were significantly lower than the measured values. Sensitivity studies showed that the time-dependent settlement predicted by the model is highly sensitive to the biodegradation rate of MSW. The good agreement between numerical values and observed vertical deformations for the SWEAP section on the MSW landfill suggests that the model has the potential to assess the performance of subsystems in landfills (e.g., the performance of a side slope liner system subject to landfill settlement). However, the discrepancy between predicted and observed horizontal displacements suggests that the numerical model can be improved by incorporating deviatoric creep deformations in the constitutive model.

A constitutive model for municipal solid waste incorporating bounding surface plasticity and reinforcing effect

Seismic stability of municipal solid waste (MSW) landfills is of vital importance and increasingly encouraged to be analyzed through numerical modeling where a rational definition of the stress-strain relationship of MSW is essentially required. The complicated constituents and existence of fibrous materials lead to mechanical behaviors totally different from general soils. In this study, a constitutive model is proposed to describe the dynamic response of MSW. This model is based on the double-phase assumption, i.e. the behaviors of the MSW whole are governed by the basic and fibrous phase. The basic phase is described with a bounding surface plasticity model considering the degradation effect under dynamic loadings, and the fibrous phase is described with a pressure-dependent elastic model. An explicit integration algorithm with automatic error control is applied to solve it. The coupling of these two constitutive models facilitates the continuous development of effective stress path over the critical state line, which reflects the reinforcing effect of fibrous materials. Furthermore, the compression of MSW particles is considered for undrained conditions, enabling the accurate calculation of effective stress. This model is verified through comparison with triaxial test results and its features are demonstrated through parametric studies and application in specific problems.

Modified Model for Municipal Solid Waste in Simulated Controlled Sanitary and Bioreactor Landfills

Modified Model for Municipal Solid Waste in Simulated Controlled Sanitary and Bioreactor Landfills

A coupled hydro-mechanical-biodegradation model for municipal solid waste in leachate recirculation

The weight of Municipal solid waste (MSW) leads to a decrease of void ratio in landfill with depth and the biodegradation of MSW also results in decrease of void ratio with time. The spatial and temporal changes of void ratio of MSW have significant effects on its hydraulic properties and consequently influence the leachate recirculation process. In this paper, an advanced coupled hydro-mechanical-biodegradation (H-M-B) model is proposed to analyze the full coupling process for leachate recirculation taking into account the effect of initial density profile and its change due to biodegradation. A new solver is presented using the finite volume method based on the OpenFOAM platform to implement the coupled H-M-B model. The volume change caused by effective stress, degree of saturation and degradation, and the effect of void ratio change on hydraulic properties, can be taken into account in the coupled H-M-B model. The results calculated by the coupled H-M-B model illustrate the effect of void ratio on hydraulic properties, and the effect of compressibility, initial density and biodegradation on leachate recirculation. This study will contribute to the understanding of the leachate recirculation process and enhance the design of MSW landfills.

Sustainable recycling model for municipal solid waste in Patna

Sustainable development is a major concern for developing nations as they strive to preserve their ecological balance along with economic growth. It has been noticed that economic growth results in environmental degradation as it influences lifestyle practices and leads to increased consumption of goods thus generating the large volume of municipal solid waste. Patna, the capital city of Bihar, is an ideal example of this condition. Here, central and local government and pollution committees fail to effectively tackle the large and increasing volume of municipal solid waste. Such scenario of municipal solid waste management in the city can cause serious health hazards, environmental degradation, and ecological destruction. Recycling the inorganic fraction of municipal solid waste can reduce the threat. In the present study, based on an extensive literature review propose a theoretical sustainable recycling model for Patna. This model is based on the similitudes in the recommendations required to attain ‘sustainable development’ and ‘sustainable recycling’. Sustainable recycling model has six gears drive by various variables. Each gear has been tested for its existence in Patna. As a result, ‘social aspect gear drive by three variables in sustainable recycling model is public health; public awareness; health of workers involves in recycling’ shows complete non-existence behaviour. Hence, a survey ( n = 127) has been performed to evaluate the success factors for social aspect gear existence in sustainable recycling model. Multivariate statistical analysis has been executed the comparison of respondents’ perception on success factors and success factor groups affecting sustainable recycling of municipal solid waste in Patna. The study contends that if the proposed model has been successfully applied, then the problem of municipal solid waste can be effectively addressed.

An equivalent-time-lines model for municipal solid waste based on its compression characteristics

Municipal solid waste (MSW) demonstrates a noticeable time-dependent stress–strain behavior, which contributes greatly to the settlement of landfills and therefore influences both the storage capacity of landfills and the integrity of internal structures. The long-term compression tests for MSW under different biodegradation conditions were analyzed. It showed that the primary compression can affect the secondary compression due to the biodegradation and mechanical creep. Based on the time-lines model for clays and the compression characteristics of MSW, relationships between MSW’s viscous strain rate and equivalent time were established, and then the viscous strain functions of MSW under different biodegradation conditions were deduced, and an equivalent-time-lines model for MSW settlement for two biodegradation conditions was developed, including the Type I model for the enhanced biodegradation condition and the Type II model for the normal biodegradation condition. The simulated compression results of laboratory and field compression tests under different biodegradation conditions were consistent with the measured data, which showed the reliability of both types of the equivalent-time-lines model for MSW. In addition, investigations of the long-term settlement of landfills from the literature indicated that the Type I model is suitable for predicting settlement in MSW landfills with a distinct biodegradation progress of MSW, a high content of organics in MSW, a short fill age or under an enhanced biodegradation environment; while the Type II model is good at predicting settlement in MSW landfills with a distinct progress of mechanical creep compression, a low content of organics in MSW, a long fill age or under a normal biodegradation condition. Furthermore, relationships between model parameters and the fill age of landfills were summarized. Finally, the similarities and differences between the equivalent-time-lines model for MSW and the stress-biodegradation model for MSW were discussed.

Constitutive model for municipal solid waste considering the effect of biodegradation

With large-scale construction of landfills, the study of the properties of municipal solid waste (MSW) has become an important subject. The objective of this study is to propose a new constitutive model for MSW considering the effect of biodegradation. The indicators representing the degree of biodegradation are first discussed, and the impact of biodegradation on the mechanical properties of MSW is then formulated in volumetric strain by introducing a biodegradation-induced void change parameter, which provides a fundamental understanding of the change in waste properties with long-term biodegradation. On the basis of this, a constitutive model is developed following the framework of critical state soil mechanics, and the proposed model is validated by comparing simulations and experimental data of triaxial tests and of a long-term settlement experiment. Finally, the effects of MSW composition and biodegradation are analysed by parametric studies.

A particle scale model for municipal solid waste and refuse-derived fuels pyrolysis

The solid phase decomposition during pyrolysis of municipal solid waste (MSW) and refuse-derived fuels (RDF) is modelled on particle scale accounting for heat and mass transfer. Waste pyrolysis is expressed as a linear combination of pyrolysis of its components. The novel characterization method used expresses waste composition in terms of three reference species. The selected species are a mixture of cellulose and hemicellulose, a mixture of polystyrene and polyethylene terephthalate, and a mixture of polyethylene and polypropylene. The pyrolysis kinetics models for these components are taken from the literature. The fractions of the components in the mixtures are optimized to fit the model to non-isothermal mass loss curves from selected experimental reports. The particle scale model has been evaluated against experimental transient temperature profiles at the centre of a large waste pellet during pyrolysis. The model is able to predict the main trend, but shows a more fluctuating temperature curve.

One-dimensional model for municipal solid waste (MSW) settlement considering coupled mechanical-hydraulic-gaseous effect and concise calculation

A new model entitled the coupled mechanical-hydraulic-gaseous effect and biochemical degradation for municipal solid waste (MSW) is proposed to simulate and predict the MSW settlement in this study. The coupled model can be used to simulate and predict the distributions of gas and water pressure as well as total waste settlement. Model verification indicates that because of degradation, the excess pore gas pressure increases rapidly and reaches a peak value in a short time, and then it dissipates gradually. But the excess pore water pressure may not always increase at the beginning, which depends on hydraulic conductivity of MSW. Dissipation of the excess pore water pressure is slower than that of the excess pore gas pressure. A waste settlement experiment was conducted in the laboratory using a synthetic MSW. The data was used to verify the developed model, which gave satisfactory results. Based on the experimental results, a new formula is proposed to simulate biochemical degradation.

Constitutive model for municipal solid waste incorporating mechanical creep and biodegradation-induced compression

A constitutive model is proposed to describe the stress-strain behavior of municipal solid waste (MSW) under loading using the critical state soil mechanics framework. The modified cam clay model is extended to incorporate the effects of mechanical creep and time dependent biodegradation to calculate total compression under loading. Model parameters are evaluated based on one-dimensional compression and triaxial consolidated undrained test series conducted on three types of MSW: (a) fresh MSW obtained from working phase of a landfill, (b) landfilled waste retrieved from a landfill after 1.5 years of degradation, and (c) synthetic MSW with controlled composition. The model captures the stress-strain and pore water pressure response of these three types of MSW adequately. The model is useful for assessing the deformation and stability of landfills and any post-closure development structures located on landfills.

Prediction of Long-Term Municipal Solid Waste Landfill Settlement Using Constitutive Model

This paper proposes a generalized constitutive model for municipal solid waste, based on the framework derived from critical state concepts and incorporating the effects of mechanical creep and time-dependent biodegradation, to predict total landfill compression under incremental loading and with time. The model parameters are calculated based on laboratory one-dimensional compression and triaxial compression tests, and data available from published literature. To illustrate the applicability of the proposed model, settlements due to incremental loading of waste with time are predicted for typical landfill conditions. The predicted settlement results using the proposed model are compared with the predicted settlement results using 14 different reported models. It is shown that the predicted settlements can vary significantly depending on the model used and the parameter values selected. The proposed model predicts the total settlement in a range similar to the reported models that consider all three compo...

Constitutive model for long term municipal solid waste mechanical behavior

This paper presents some improvements in the model proposed by Machado et al. [Machado SL, Carvalho MF, Vilar OM. Constitutive model for municipal solid waste. J Geotech Geoenviron Eng ASCE 2002;128(11):940–51] now considering the influence of biodegradation of organic matter in the mechanical behavior of municipal solid waste. The original framework considers waste as composed of two component groups; fibers and organic paste. The particular laws of behavior are assessed for each component group and then coupled to represent waste behavior. The improvements introduced in this paper take into account the changes in the properties of fibers and mass loss due to organic matter depletion over time. Mass loss is indirectly calculated considering the MSW gas generation potential through a first order decay model. It is shown that as the biodegradation process occurs the proportion of fibers increases, however, they also undergo a degradation process which tends to reduce their ultimate tensile stress and Young modulus. The way these changes influence the behavior of MSW is incorporated in the final framework which captures the main features of the MSW stress–strain behavior under different loading conditions.

A composite model for municipal solid waste

AbstractThe mechanical behaviour of municipal solid waste is very complex due to the internal structure and differs considerably from ordinary materials. The fundamental idea of the presented mechanical constitutive model is the split of the material into two solid phases, justified by experimental observations, where fibrous particles signi.cantly influence the composite behaviour. Constitutive laws are independently introduced for each phase. A .nite deformation theory is applied, whereas the concept of elastoplasticity allows reproducing the highly non‐linear stress‐strain relations. A creep law describes time‐depending deformation under compression loads. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Constitutive Model for Municipal Solid Waste

Municipal solid waste (MSW) is a refuse composed of various materials with different properties. Some of the components are stable while others degrade as a result of biological and chemical processes. These aspects impart to MSW a complex behavior that has been modeled, with many limitations, within the concepts of soil mechanics. In this paper, a framework to model the MSW mechanical behavior is proposed based on results from laboratory tests, such as triaxial compression and confined compression of large samples. It is suggested that two different effects command MSW mechanical behavior: (a) the reinforcement of MSW by synthetic fibers (composed by many types of polymers) and (b) the behavior of the MSW paste, without fibers. Accordingly, two distinct frameworks were used to represent the main MSW characteristics: (a) a critical state framework for MSW paste and (b) an elastic perfectly plastic framework for waste fibers, with a time lag for fiber loading (function fm). The proposed model is capable of...