Response Of Municipal Solid Waste Research Articles

Compression Behavior of Municipal Solid Waste in Temperature-Controlled Isotropic Condition

Abstract The mechanical response of municipal solid waste (MSW) under different types of loading and testing conditions has been explored by many researchers. However, the effect of temperature on MSW compressibility has yet to be investigated. Temperature enhancement is well-known in landfill engineering, mainly when the bioreactor philosophy is employed. The generated heat gradients affect the solid particles and fluid phases. As a result, the mechanical response of MSW will be different compared with the most recent research results. Only a few investigations have been conducted on the impact of temperature on MSW’s mechanical response. This research shows how temperature enhancement impacts the compression behavior of MSW specimens with different compositions. A large-scale temperature-controlled triaxial device capable of imposing temperatures up to 85°C has been used. It is shown that, with increasing temperature, the compressive strains for MSW increase. However, the waste composition, mainly the MSW plastic content, also affects these strains. The temperature enhancements increase the mechanical creep and immediate compression indexes but decrease the samples’ elastic rebound and swelling index. Furthermore, the paper analyzes how pore water pressure affects the effective stress in such varying temperature conditions considering the waste particles’ compressibility. The achieved values show that the pore water pressure effect on effective stress is reduced up to 75 % because of the particles’ compressibility. The permeability of samples was examined based on the isotropic compression results. The results confirmed that MSW’s permeability depends on the plastic content, applied confining stress, and temperature. Increasing the temperature level showed a reduction in the permeability of samples. However, this difference was not paramount.

SHEAR STRENGTH CHARACTERISTICS OF FIBROUS SOLID WASTE MATERIALS IN LANDFILL SITES

Slope-stability failures have occurred in several improper landfills and illegaldumping sites. To investigate the shear response of municipal solid waste (MSW), it issignificant to consider the stability of dumping site and landfill design. In the present paper,the shear response and shear strength of MSW recovered from four different landfill sites (inJapan and China) were investigated using a developed in-situ direct shear test apparatus.Moreover, the pa-per introduces the steps for preparation of undisturbed samples and testprocedures in details to determine the in-situ shear strength characteristics (c and φ) of MSW.The in-situ experimental results indicated that the shear response of waste materials affectedby the existence of fibrous materials. In addition, the values of cohesion and frictionparameters of waste materials strongly depended on the percent of fibrous materials. Resultsof geotechnical investigations and slope stability studies of landfill sites have been alsointroduced.

Influence of dynamic coupled hydro-bio-mechanical processes on response of municipal solid waste and liner system in bioreactor landfills

A two-dimensional (2-D) mathematical model is presented to predict the response of municipal solid waste (MSW) of conventional as well as bioreactor landfills undergoing coupled hydro-bio-mechanical processes. The newly developed and validated 2-D coupled mathematical modeling framework combines and simultaneously solves a two-phase flow model based on the unsaturated Richard’s equation, a plain-strain formulation of Mohr-Coulomb mechanical model and first-order decay kinetics biodegradation model. The performance of both conventional and bioreactor landfill was investigated holistically, by evaluating the mechanical settlement, extent of waste degradation with subsequent changes in geotechnical properties, landfill slope stability, and in-plane shear behavior (shear stress-displacement) of composite liner system and final cover system. It is concluded that for the given specific conditions considered, bioreactor landfill attained an overall stabilization after a continuous leachate injection of 16years, whereas the stabilization was observed after around 50years of post-closure in conventional landfills, with a total vertical strain of 36% and 37% for bioreactor and conventional landfills, respectively. The significant changes in landfill settlement, the extent of MSW degradation, MSW geotechnical properties, along with their influence on the in-plane shear response of composite liner and final cover system, between the conventional and bioreactor landfills, observed using the mathematical model proposed in this study, corroborates the importance of considering coupled hydro-bio-mechanical processes while designing and predicting the performance of engineered bioreactor landfills. The study underscores the importance of considering the effect of coupled processes while examining the stability and integrity of the liner and cover systems, which form the integral components of a landfill. Moreover, the spatial and temporal variations in the landfill settlement, the stability of landfill slope under pressurized leachate injection conditions and the rapid changes in the MSW properties with degradation emphasizes the complexity of the bioreactor landfill system and the need for understanding the interrelated processes to design and operate stable and effective bioreactor landfills. A detailed discussion on the results obtained from the numerical simulations along with limitations and key challenges in this study are also presented.

Constant load and constant volume response of municipal solid waste in simple shear

Constant load and constant volume simple shear testing was conducted on relatively fresh municipal solid waste (MSW) from two landfills in the United States, one in Michigan and a second in Texas, at respective natural moisture content below field capacity. The results were assessed in terms of two failure strain criteria, at 10% and 30% shear strain, and two interpretations of effective friction angle. Overall, friction angle obtained assuming that the failure plane is horizontal and at 10% shear strain resulted in a conservative estimation of shear strength of MSW. Comparisons between constant volume and constant load simple shear testing results indicated significant differences in the shear response of MSW with the shear resistance in constant volume being lower than the shear resistance in constant load. The majority of specimens were nearly uncompacted during specimen preparation to reproduce the state of MSW in bioreactor landfills or in uncontrolled waste dumps. The specimens had identical percentage of <20mm material but the type of <20mm material was different. The <20mm fraction from Texas was finer and of high plasticity. MSW from Texas was overall weaker in both constant load and constant volume conditions compared to Michigan waste. The results of these tests suggest the possibility of significantly lower shear strength of MSW in bioreactor landfills where waste is placed with low compaction effort and constant volume, i.e., “undrained”, conditions may occur. Compacted MSW specimens resulted in shear strength parameters that are higher than uncompacted specimens and closer to values reported in the literature. However, the normalized undrained shear strength in simple shear for uncompacted and compacted MSW was still higher than the normalized undrained shear strength reported in the literature for clayey and silty soils.

Response of Municipal Solid Waste to Mechanical Compression

AbstractThe compressibility of municipal solid waste (MSW) is of engineering interest as it affects the short-term and long-term performance of landfills, as well as their expansion, closure, and postclosure development. An assessment of the field settlement behavior of MSW can be reliably executed only when the various mechanisms contributing to the settlement are properly taken into account. A comprehensive large-size experimental testing program that involved a total of 143 one-dimensional compression tests from five landfills, in Arizona, California, Michigan, and Texas of the United States as well as Greece was executed to systematically assess the compressibility characteristics of MSW subjected to a compressive load. Emphasis is given to the influence of waste structure, waste composition, unit weight, and confining stress on the compressibility parameters that are used in engineering practice, such as the constrained modulus and compression ratio, as well as long-term compression ratio due to mech...

Characterizing a Brazilian sanitary landfill using geophysical seismic techniques

Two different geophysical techniques, namely crosshole and multichannel analysis of surface waves – MASW, were applied to investigate the mechanical response of Municipal Solid Waste buried under humid, subtropical climate. Direct investigations revealed that the buried waste was composed mainly of soil-like material (51%) and plastics (31%) with moisture content average values of 43% near the surface and 53% after around 11m depth. Unit weight varied between 9kN/m3 and 15kN/m3. Seismic investigation of the landfill yielded shear wave velocities (VS) estimated from the crosshole tests ranging from 92 to 214m/s, while compression wave velocities (VP) ranged from 197 to 451m/s. Both velocities were influenced by vertical confining stress and thus tended to increase with depth. VS calculated from MASW tests were lower than the ones calculated from the crosshole tests, probably due to the different frequencies used in the tests. The results of both methods tended to configure a lower bound to the values reported in the technical literature in general, as expected for low compaction waste with small amounts of cover soil. Although VS did not show abrupt changes with depth, VP profile distribution combined with direct investigations results, such as temperature, in-place unit weight and moisture content, suggest that the waste body could be divided into two strata. The lower one is poorly drained and shows higher moisture content, as a consequence of the operational techniques used in the first years, while the upper stratum is probably related to a better drained waste stratum, resulting from the improvement of operational standards and increase in drainage facilities throughout the years.

Implications of variable waste placement conditions for MSW landfills

This investigation was conducted to evaluate the influence of waste placement practices on the engineering response of municipal solid waste (MSW) landfills. Waste placement conditions were varied by moisture addition to the wastes at the time of disposal. Tests were conducted at a California landfill in test plots (residential component of incoming wastes) and full-scale active face (all incoming wastes including residential, commercial, and self-delivered components). The short-term effects of moisture addition were assessed by investigating compaction characteristics and moisture distribution and the long-term effects by estimating settlement characteristics of the variably placed wastes. In addition, effects on engineering properties including hydraulic conductivity and shear strength, as well as economic aspects were investigated. The unit weight of the wastes increased with moisture addition to a maximum value and then decreased with further moisture addition. At the optimum moisture conditions, 68% more waste could be placed in the same landfill volume compared to the baseline conditions. Moisture addition raised the volumetric moisture content of the wastes to the range 33–42%, consistent with values at and above field capacity. Moisture transfer occurred between consecutive layers of compacted wastes and a moisture addition schedule of 2days of as-received conditions and 1day of moisture addition was recommended. Settlement of wastes was estimated to increase with moisture addition, with a 34% increase at optimum moisture compared to as-received conditions. Overall, moisture addition during compaction increased unit weight, the amount of incoming wastes disposed in a given landfill volume, biological activity potential, and predicted settlement. The combined effects have significant environmental and economic implications for landfill operations.

Approach for the use of MSW settlement predictions in the assessment of landfill capacity based on reliability analysis

In the analysis and design of municipal solid waste (MSW) landfills, there are many uncertainties associated with the properties of MSW during and after MSW placement. Several studies are performed involving different laboratory and field tests to understand the complex behavior and properties of MSW, and based on these studies, different models are proposed for the analysis of time dependent settlement response of MSW. For the analysis of MSW settlement, it is very important to account for the variability of model parameters that reflect different processes such as primary compression under loading, mechanical creep and biodegradation. In this paper, regression equations based on response surface method (RSM) are used to represent the complex behavior of MSW using a newly developed constitutive model. An approach to assess landfill capacities and develop landfill closure plans based on prediction of landfill settlements is proposed. The variability associated with model parameters relating to primary compression, mechanical creep and biodegradation are used to examine their influence on MSW settlement using reliability analysis framework and influence of various parameters on the settlement of MSW are estimated through sensitivity analysis.

Drained response of municipal solid waste in large-scale triaxial shear testing

A comprehensive laboratory investigation was performed on municipal solid waste (MSW) from a landfill located in northern California using a large-scale triaxial (TX) apparatus. An improved, standardized waste specimen preparation method was developed and used to prepare 27 large-scale TX specimens (d=300mm, h=600–630mm). The effects of waste composition, confining stress, unit weight, loading rate, and stress path on the drained stress–strain response of MSW were investigated. Waste composition has a significant effect on its stress–strain response. The commonly observed upward curvature of the stress–strain response of specimens composed of larger-sized waste materials results from the fibrous constituents (primarily paper, plastic and wood) reinforcing the waste matrix. This effect is greatest when the MSW specimen is sheared across the long axis of the fibrous particles. Due to this significant strain hardening effect and waste’s in situ stress state, a limiting strain failure criterion of 5% axial strain from the Ko field consolidation state is judged to be most appropriate. Results from this test program and data from the literature indicate that the TX compression secant friction angle of MSW varies from 34° to 44°, with 39° as a best estimate, at a confining stress of one atmosphere (assuming c=0). The friction angle decreases as confining stress increases. The friction angles measured in this testing program are representative of failure surfaces that are oriented at an angle to the predominant orientation of the long axis of the fibrous waste particles. These friction angles are higher than those obtained in direct shear tests where shearing typically occurs parallel to the orientation of the fibrous waste particles.

Deer Track Bioreactor Experiment: Field-Scale Evaluation of Municipal Solid Waste Bioreactor Performance

AbstractThe Deer Track Bioreactor Experiment (DTBE) was a field-scale experiment conducted in a drainage lysimeter (8.2-m height, 2.4-m diameter) to assess the physical, chemical, and biological response of municipal solid waste with leachate addition. The experiment was operated for 1,067 days, with leachate dosing initiated on Day 399. Fresh leachate collected from a full-scale landfill was used for each dose. The ratio of cumulative leachate effluent to influent volume increased during dosing and leveled off at approximately 80%, indicating field capacity was achieved. Peak Darcy flux ranged from 2×10-7 m/s to 4×10-5 m/s, with larger flux computed for the last four doses when waste saturation was higher. During the experiment, the average dry unit weight of the waste increased 28% and the dry-weight water content (wd) increased 18%; field capacity of the waste was 44 to 48% on a dry-weight basis. Biochemical methane potential decreased from 51.4 to 3.4 mL-CH4/g-dry, indicating that 93% of the potent...