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Article

Characterization of Physicochemical and Mechanical Properties of Dumped Municipal Solid Waste in Sri Lanka as Affected by the Climate Zone and Dumping Age

by
Muhammad Rashid Iqbal
1,2,
Abeywickrama Bamunusin Kankanamge Thilini Piumali
3,
Nadeej Hansaraj Priyankara
4,
Alagiyawanna Mohottalalage Nayana Alagiyawanna
5,
Laksiri Chandana Kurukulasuriya
6 and
Ken Kawamoto
2,7,*
1
Department of Civil Engineering Technology, National Skills University, Faiz Ahmed Faiz Road, Islamabad 44000, Pakistan
2
Graduate School of Science and Engineering, Saitama University, 255 Shimo-Okubo, Sakura-ku, Saitama 338-8570, Japan
3
Sri Lanka Ports Authority, No. 19, Chaithya Road, Colombo P.O. Box 59, Sri Lanka
4
Department of Civil and Environmental Engineering, Faculty of Engineering, University of Ruhuna, Hapugala, Galle 80000, Sri Lanka
5
Department of Construction Technology, Faculty of Technology, Wayamba University of Sri Lanka, B308 Negombo-Kurunegala Road, Kuliyapitiya 60170, Sri Lanka
6
Department of Civil Engineering, Faculty of Engineering, University of Peradeniya, Peradeniya 20400, Sri Lanka
7
Innovative Solid Waste Solutions (Waso), Hanoi University of Civil Engineering, No. 55 Giai Phong Street, Hai Ba Trung District, Hanoi 11616, Vietnam
*
Author to whom correspondence should be addressed.
Sustainability 2022, 14(8), 4706; https://doi.org/10.3390/su14084706
Submission received: 18 March 2022 / Revised: 6 April 2022 / Accepted: 11 April 2022 / Published: 14 April 2022
(This article belongs to the Special Issue Circular Economy from the Perspective of Technology and Management for Waste)
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Review Reports Versions Notes

Abstract

:
Due to the rapid increase in population and urbanization, municipal solid waste (MSW) generation is increasing. Sri Lanka, in particular, faces serious difficulties in finding new sites for MSW disposal, due to the lack of available space; therefore, the rehabilitation of existing MSW dumping sites and the extension of their services are required to achieve sustainable urban development. To examine suitable rehabilitation techniques, it is essential to identify the physicochemical and mechanical properties of dumped MSW, fully considering climatic conditions, waste composition, and the time since the waste was dumped. In this study, therefore, the physicochemical and mechanical properties of dumped MSW were investigated; the dumped MSW was taken from existing MSW dumping sites in three climate zones in Sri Lanka, namely the Karadiyana site in the wet zone, Udapalatha in the intermediate zone, and Hambantota in the dry zone, and it was taken at different times after being dumped. The results showed that the waste composition and biodegradation of organic materials affected the physicochemical and mechanical properties of the dumped waste. The measured compaction parameters of the “old” sites at Udapalatha and Hambantota were higher compared to the “new” sites. Compaction parameters at the Karadiyana site, on the other hand, were low, at even >20 years since being dumped, probably due to the high amount of scarcely compacted materials. In direct shear tests, both strain hardening and softening of the waste samples were observed, depending on the difference in vertical stress. Based on the Pearson correlations among measured physicochemical and mechanical parameters, it was found that the loss on ignition (LOI) would be a good indicator to quickly assess the mechanical parameters of “new” and “old” waste materials, due to the small sensitivities to waste age and climate conditions in Sri Lanka. In particular, LOI correlated well to measured specific gravity and compaction properties, and the r2 values of correlations exceeded |0.80|.

1. Introduction

The implementation of the ‘reduce, reuse, and recycle’ concept is essential to establish a sound waste management system for sustainable urban development and to achieve a circular economy in a society [1,2,3]. Most developing countries, however, are facing severe environmental and social problems due to the open dumping of municipal solid waste (MSW), a common waste disposal method in developing countries, due to many factors such as lack of technical skills and economic and social obstacles [4,5]. Moreover, local authorities who have the responsibility to manage the generated MSW are facing serious difficulties in finding available new land for MSW disposal, especially in expanding urban areas with rapid increases in population [6,7,8].
One practical option to solve the environmental and social problems induced by MSW open dumping is to rehabilitate existing MSW dumping sites and to extend their capacity for dumped MSW (i.e., service time), preventing secondary environmental pollution and slope failure (landslides) [8,9,10]. To implement the rehabilitation of MSW dumping sites, a combinational engineering approach should be carried out, including the following: excavation and compaction of buried waste to reduce the volume of waste and slope cut; ground leveling to avoid landslides; an earthen cover to prevent waste scattering and intrusion of surface water; improvement of ground strength; and control of environmental pollution (treatment of landfill leachate and groundwater) [11,12]. The rehabilitation of existing MSW landfills, moreover, would contribute to the post-closure land uses of MSW dumping sites [13,14].
Many studies have been conducted to characterize the physicochemical and mechanical properties of dumped MSW by laboratory tests using samples taken from MSW dumping sites [15,16,17,18,19,20,21] and field investigations [13,22,23,24,25,26]. For example, Zekkos et al. [27] investigated the depth profile of unit weight (i.e., density) of buried waste at MSW dumping sites; the study used reported data and showed that the unit weight increased with age after dumping and depth. Moreover, a careful definition through a constitutive relationship based on a three-phase model (solid, liquid, and gas) was performed by Stolz et al. [28]. With regard to mechanical properties, previous studies investigated compressibility and shear strength (drained and undrained) mainly by compaction and direct shear tests. Reddy et al. [11,25] showed that compacted densities decreased with age after dumping and that the cohesion of tested waste samples varied greatly by the presence of biodegradable organic materials. Zekkos et al. [27] also reported that biodegradable organic materials were good indicators of compressibility and shear strength, and higher organic contents in MSW gave higher compressibility and lower shear strength. Stolz et al. [29,30] characterized the water retention properties, pore size distribution, and gas permeability of MSW samples under compression. Zhan at al. [10] carefully measured the shear strength of dumped MSW of different ages and showed that the cohesion decreased and internal friction increased with the age of MSW. Ramaiah et al. [31] also reported that cohesion decreased and internal friction increased with an increase in the fill age of MSW. Gabr et al. [32], on the other hand, investigated the shear strength of buried MSW samples in MSW landfills with a leachate circulation system and found that both the cohesion and internal friction of waste samples decreased with age since the waste was dumped (i.e., an increase in biodegradation of organic materials). In addition, Machado et al. [33,34,35] investigated the effects of biodegradation on the mechanical properties of MSW and found that easily biodegradable organic materials decreased the shear strength of “young/fresh” MSW, but that fiber materials increased the shear strength of MSW with the increasing decomposition of organic materials. They also suggested that the biodegradation generated the fibrous materials that reduced the ultimate tensile strength and Young’s modulus.
In general, difficulties in characterizing the physicochemical and mechanical properties of dumped MSW, as well as a wide range of values for mechanical properties in previous studies, are attributed to the wide variation in the composition and configuration of dumped MSW in countries and regions with different climate zones (i.e., heterogeneity of materials), and inclusion of both biodegradable and non-biodegradable (inert) materials in dumped MSW. All these characteristics affect not only the laboratory testing results of physicochemical and mechanical properties but also the long-term performance and behavior of the MSW dumping sites, thus emphasizing the importance of studies on the “site-specific” characteristics of dumped MSW.
Among developing countries, Sri Lanka has very limited available land for the establishment of new MSW landfills, and most of the MSW collected from local authorities has been disposed of at existing open dumping sites [13,36]. During rainy seasons, many slopes collapse at MSW dumping sites every year. In particular, a big collapse of the MSW dumping site at Meethotamulla, Colombo on 14 April 2017 caused enormous damage, with 32 casualties and huge property destruction [13]. Currently, the MSW generation per capita per day is reported as 0.4–1.0 kg [37], and urban population as ~19% [38]; however, it can be estimated that the MSW generation increases due to the rapid urbanization and growth in population. Thus, the rehabilitation of existing open MSW dumping sites to extend their service life, and the construction of new sites for MSW disposal, are an urgent issue in Sri Lanka. In addition, Sri Lanka has three distinct climate zones: wet, intermediate, and dry zones, which are categorized by annual rainfall (annual rainfall: >2500 mm in the wet zone, 1500–2000 mm in the intermediate zone, and 800–1200 mm for the dry zone) [39]. This means that the “site-specific” characteristics of dumped MSW should be fully considered when we rehabilitate existing and construct new MSW disposal sites.
The objectives of this study, therefore, were (1) to characterize the physicochemical and mechanical properties of dumped MSW, taken from existing MSW dumping sites in three climate zones in Sri Lanka (Karadiyana site in the wet zone, Udapalatha in the intermediate zone, and Hambantota in the dry zone), with different periods after dumping (<3 years after being dumped (young) and >3 years after being dumped (old)), including additional data analyses and discussion based on previously published measurements [40] and the literature, and (2) to examine the relationships among measured physicochemical parameters and mechanical parameters.

2. Materials and Methods

2.1. Sampling Locations

Waste samples were collected from three MSW dumping sites: (a) Karadiyana, (b) Udapalatha, and (c) Hambantota in Sri Lanka. The sampling was carried out in March 2017 at the Karadiyana site, and from March to May 2013 at the Udapalatha and Hambantota sites. The sampling locations and photographs are shown in Figure 1, with site information such as daily waste intake and climatic zones. The Karadiyana site is located in the wet zone, the Udapalatha site is located in the intermediate zone, and the Hambantota site is located in the dry zone [39]. Based on the number of years since the waste was dumped, the MSW was labeled in this study as “New” (<3 years since being dumped) or “Old” (>3 years since being dumped) (Table 1). Waste samples of ~50 kg were taken from waste layers at 1 m depth intervals (Udapalatha and Hambantota sites) or 2 m depth intervals (Karadiyana site). Subsoil below the waste layer was also taken from the Udapalatha and Hambantota sites. At the Karadiyana site, a soil sample at the depth of 2–3 m was also taken from the original ground. Among samples tested in this study, the samples from the Karadiyana site were the oldest, and the waste was more than 20 years old (according to the interview with the Waste Management Authority of the Western Province in Sri Lanka [41]).

2.2. Waste Composition and Physicochemical Properties

Waste composition was determined following ASTM D5231-92 (2016) [15] and Dixon and Langer (2016) [43]. The samples were sorted by hand and sieved with a set of sieves of 9.5, 4.74, and 2 mm, as shown in Figure 2. In addition to waste composition analysis, a sieve analysis was carried out to determine the particle size distribution (PSD) of particles greater than 0.075 mm, according to ASTM C136/C136M-19 [16], and the hydrometer test for particle size was less than 0.075 mm. Specific density (Gs) of the samples was determined, according to ASTM D854-14 [17], and the loss on ignition (LOI) test according to ASTM D 7348-13 [18] determined the organic content of the dumped MSW. Atterberg limit tests were carried out to determine the liquid and plastic limits of the samples, according to ASTM D4318-17e1 [19]. The pH of the waste materials was determined according to ASTM D472-19 [20], and the electrical conductivity was tested to conform with JGS 0212-2009 [21].

2.3. Compaction and Direct Shear Tests

Sieved samples <9.5 mm were used for compaction and direct shear tests. For the compaction test, the sample was packed into a mold with a diameter and height of 10 cm in three equal layers with a rammer of 2.5 kg and a drop height of 305 mm to determine the maximum dry unit weight (γd) and optimum moisture contents (wopt) (standard compaction energy of 600 kN m/m3 [44]. Direct shear tests [45] were conducted to determine the cohesion and internal friction angle for the tested sample in a mold with 100 mm diameter and 40 mm height. First, the tested samples were compacted in a mold to the desired degree of compaction (~90%) by adjusting the initial water content of samples to the approximately optimum water contents (wopt; see Table 3). Horizontal and vertical displacement transducers were attached the data logger to monitor the shear displacement and vertical strain. A constant strain rate of 0.15 mm/min was used to shear the samples under three different vertical stress conditions of 25 kPa, 50 kPa, and 75 kPa. The direct shear test apparatus is shown in Figure 3.

3. Results and Discussion

3.1. Waste Composition and Particle Size Distribution

The waste composition of the tested materials is shown in Table 2. For all tested samples, there were no obvious easily biodegradable organic materials (e.g., kitchen waste) because those materials became residues (2–4.75 mm and <2.0 mm) after biodegradation by mixing with fine materials such as sand and crushed inert materials. It is noted that fresh MSW in Sri Lanka is normally rich in kitchen waste containing easily biodegradable organic materials (e.g., ~70% of the fresh MSW contains kitchen waste). For all the investigated sites, the % of residue (2–4.75 mm and <2.0 mm) was the highest among all constituents. In particular, the sum of “Gravel” and “Residues” exceeded 80% at the Hambantota sites (new and old), meaning that the dumped waste was very small, inert materials that are hard to biodegrade, such as plastic, vinyl, and glass. For the Karadiyana and Udapalatha sites, on the other hand, those inert dumped materials that are hard to biodegrade comprised some % of the total; “Glass and Wood” were rich in Karadiyana, and “Cementitious materials” and “Vinyl” were rich in the new Udapalatha site. Measured PSD curves for dumped waste are shown in Figure 4. It can be clearly seen that the sample from the Karadiyana site was richer in coarse fraction >9.5 mm compared to the other sites. Those coarse fractions mainly consisted of large pieces of “Ceramic”, “Rubber and Textile”, and “Metals” (Figure 2).

3.2. Physicochemical Properties

Measured physicochemical properties are summarized in Table 1, and their depth profiles are shown in Figure 5. In order to compare the measured physicochemical and mechanical properties in this study, data in reports from Sri Lanka, Karadiyana, and Jaffna MSW dumping sites [42], were tabulated The values of field gravimetric water content (wf) for the waste layers were 50–120% at the Karadiyana site (wet climate zone) and the Udapalatha site (intermediate climate zone). For the Hambantota site located in the dry zone, on the other hand, the wf values were approximately 20–60%. The measured pH values for waste layers at all sites, including subsoil and the original ground, did not vary much and ranged mostly from 6 to 8. All the tested samples were non-plastic or low plasticity with a plastic index (IP) < 20.
The site-specific characteristics of waste samples were clearly shown in the depth profiles of the measured specific gravity (Gs), electric conductivity (EC), and LOI. The Udapalatha sites (new and old) (Figure 5a) gave smaller Gs and higher EC and LOI values (especially those for the Udapalatha new site) compared to those of the Hambantota sites (new and old) (Figure 5c). This means that the residues of 2.0–4.75 mm and <2 mm in the waste samples from the Udapalatha site were rich in organic materials with low Gs (e.g., biodegraded kitchen waste). For the Hambantota site, on the other hand, the residues were rich in inert and inorganic materials (Table 2), resulting in high Gs values similar to those of the soil minerals (2.64–2.76 g/cm3). For the Karadiyana site (Figure 5a), the Gs values were a little higher and the EC and LOI values smaller than those for the Udapalatha site, indicating that the biodegradability of the dumped organic waste was more advanced, due to the longer period since the waste was dumped.

3.3. Mechanical Properties of Tested Samples

3.3.1. Compaction Properties

The compaction curves of the tested waste samples are shown in Figure 6, and the measured values of the maximum dry unit weight (γdmax) and optimum moisture content (wopt) are summarized in Table 3. Looking at the compaction curves of the Udapalatha and Hambantota sites, measured γd and wopt values from the old waste samples were higher compared to the new waste samples. This can be affected by the biodegradability of the dumped organic waste, i.e., “young” dumped organic waste was hardly compacted due to a cushion effect [11]. For the compaction curve of the Karadiyana site, the measured γd and wopt values were relatively low (γdmax = 10.8 kN/m3 and wopt = 39.3%), even though the sample was “old”, with >20 years since the waste was dumped. This can be mainly due to the constituents of the dumped waste, i.e., the waste of Karadiyana was rich in hardly compacted materials such as “Plastic” and “Glass and wood” compared to other waste samples tested in this study (Table 2). In particular, the waste samples of the Hambantota sites (new and old) gave higher γd values (14.1 kN/m3 for new and 16.3–17.3 kN/m3 for old) with lower wopt values (20.5% for new and 13.4–17.0% for old). This can be due to the high Gs of the residues, of 2.0–4.75 mm and <2 mm.
The typical reported values of γd and wopt for waste samples of different ages, including Sri Lankan samples [42], are also summarized in Table 3. It can be clearly seen that the γd values of “old” waste were higher than those of “young” waste. The wopt values, on the other hand, showed no relationship with tested waste age, indicating that the wopt varies highly depending on the waste constituents. Among the reported values are those of Nawagamuwa and Thirojan [42], who carried out compaction tests from Karadiyana (wet climate zone) and Jaffna (dry climate zone) waste dumping sites in Sri Lanka. It is interesting that both γd and wopt values in [42] are similar to the measured values in this study, irrespective of the difference in time since the waste was dumped (Karadiyana: 1–2 years and >20 years in this study) and the difference in the location (Jaffna in [42] and Hambantota in this study). Further studies and data are needed, but this evidence implies that the compaction properties of waste samples dumped at existing MSW sites in Sri Lanka are highly affected by the climatic condition (i.e., wet, intermediate, and dry zones).

3.3.2. Shear Strength

The experimental results of shear stress (τ) and vertical displacement (εv) as a function of shear displacement (SD) for tested waste samples at vertical stresses (σv) of 25, 50, and 75 kPa are shown in Figure 7. The measured τ increased with the increase in SD when tested at σv = 50 and 75 kPa, meaning that those samples showed strain hardening. On the other hand, the measured τ at low 25 kPa for the samples from the Udapalatha site, both new and old (Figure 7c–f), and the new samples from the Hambantota site (Figure 7g,h), showed strain softening behavior, and the peak of the τ values was observed at approximately SD = 10 mm. The strain hardening behavior could be due to the inclusion of inert fibrous materials (<9.5 mm); i.e., those materials (plastic, vinyl, leather, and rubber) contributed to the reinforcement of tested samples and helped to resist the shear displacement at σv = 50 and 75 kPa in the direct shear test [10,35]. Although the strain softening behavior was observed in some tested samples at σv = 25 kPa, those inert fibrous materials did not assist the share displacement, resulting in the gradual decrease in τ with the increasing SD.
Compared to τ–SD relationships, measured εv–SD relationships showed a big difference among the tested samples. For the Karadiyana old waste (Figure 7a,b), a small change in εv was observed at all σv conditions, indicating that no volume expansion/reduction occurred during the shear displacement process. For the Udapalatha new and old waste (Figure 7c–f), a small εv change was seen at σv = 50 and 75 kPa, but a volume expansion (negative value of εv) was observed at σv = 25 kPa. For Hambantota new and old waste (Figure 7g–j), the volume expansion/reduction was dependent on the SD range; i.e., the εv became positive (volume reduction) when SD = 0–5 mm and then the εv became negative (SD >5 mm).
Based on the measured τ–SD and εv–SD relationships in this study, cohesion (c) and internal friction (ϕ) were calculated by using Mohr’s circle [49] and are summarized in Table 3 with the reported data. The Karadiyana old waste showed the highest c and ϕ (c = 35 kPa and ϕ = 48°) among the tested samples in this study. For both the Udapalatha and Hambantota sites, the measured ϕ values for the “old” waste samples (ϕ = 29–45°) tended to become higher than those of the “new” waste samples (ϕ = 31–38°), while the measured c values for the “old” waste samples (c = 12–24 kPa) became lower than those of the “new” waste samples (c = 20–30 kPa). The results imply that the cohesion of dumped waste decreased with the time since the waste was dumped, due to the degradation of the biodegradable materials, which subsequently increased the internal friction angle with age (due to the non-degradation of inert materials).
The measured c and ϕ in this study ranged generally within the reported values (Table 3). Having a look at the Karadiyana data from Sri Lanka (wet climate zone) [42], it can be seen that the c value of the “old” waste samples in this study (c = 35 kPa) is much bigger than those of the “new” waste samples (c = 10~15 kPa), irrespective of a small difference in ϕ for both data sets. This is an opposite trend to the test data above (Udapalatha and Hambantota sites in this study), but it is supposed that the composition of tested waste samples of both studies were different. On the other hand, there were no distinct differences in c and ϕ among data from the waste samples taken from the dry zones, i.e., Hambantota in this study and Jaffna in Sri Lanka [42].
As discussed in Figure 7, the shear stress (τ) of the waste samples is dependent on the vertical stress (σv). Figure 8 shows a comparison of the measured τ in this study with the reported τ–σv relations for the MSW materials summarized by Kavazanjian [50] and Jones et al. [51]. Most of the measured τ in this study ranged in the envelope of τ–σv relationships reported by Jones et al. [51], but some data from the Karadiyana site (“old”) were higher than that of the envelope, and it can be seen that the measured τ in this study was higher than the suggested line by Kavazanjian [50]. The results strongly suggest that the mechanical properties of waste materials, including “fresh” and “old”, are highly dependent on the local conditions (i.e., site-specific), and those site-specific features, such as the climate, geography, and the management system of a dumping site, affect the mechanical properties of the waste samples.

3.3.3. Links between Physicochemical and Mechanical Parameters

In order to examine the correlations among the measured physicochemical parameters and the mechanical parameters in this study, a Pearson correlation matrix was constructed and is shown in Table 4. Among the measured physicochemical parameters in this study (Gs, LOI, pH, and EC), the LOI, overall, correlated better to the measured mechanical parameters. In particular, the r2 values of the correlations with the compaction parameters, such as the maximum dry unit weight (γdmax) and optimum moisture content (wopt), exceeded |0.80|. The LOI also correlated well with the Gs of the tested samples. It should be noted that the other physicochemical parameters (Gs, pH, and EC) were also correlated with ϕ (r2 > |0.85|); however, the correlations with other mechanical parameters (γdmax, wopt, and c) were low. This indicates that Gs, pH, and EC were not suitable indicators to characterize the mechanical properties. In addition, the LOI had moderate correlations with pH and EC (r2 > |0.60|), indicating that higher LOI samples tended to have a lower pH and higher EC, probably due to the biodegradation of the dumped MSW.
All the correlations with LOI are shown in Figure 9. In the figures, the “fresh” and “degraded” MSW samples, reported by Reddy et al. [11], and the buried MSW waste aged 2–25 years, reported by Abreu et al. [47], are also given for comparison with Gs and the compaction parameters such as γdmax and wopt. As shown in the figure, the LOI reasonably captured the mechanical parameters with linear regression lines for both “new” and “old” waste samples, irrespective of the locations in the different climate zones (small sensitivity to climate conditions). This suggests that LOI can be a convenient indicator to estimate the mechanical parameters for both “fresh” and “aged” dumped waste. It can be observed that the reported values of [11] and [46] deviated to some extent from the linear regression lines in this study (Figure 9a–c). This was maybe caused mainly by the difference of waste constituents in the tested MSW materials. Further studies are needed to discuss the links between the physicochemical and mechanical parameters of dumped waste materials, fully considering the difference in waste constituents. The easily measurable LOI, however, is expected to be a good indicator for making a quick assessment of the compaction and shear strength properties of “fresh” and “old” waste materials, and is thus able to contribute to the rehabilitation of existing MSW dumping sites in Sri Lanka.

4. Conclusions

This study aimed to 1) characterize the physicochemical and mechanical properties of dumped MSW taken from existing MSW dumping sites in three climate zones in Sri Lanka (Karadiyana site in the wet zone, Udapalatha in the intermediate zone, and Hambantota in the dry zone) with different periods after the waste was dumped (<3 years after being dumped (young) and >3 years after being dumped (old)) and 2) to examine the relationships among measured physicochemical parameters and mechanical parameters. The waste composition and biodegradation of organic materials (i.e., “age after dumping”) affected the physicochemical properties of the dumped waste. The biodegradation of organic materials also affected the compaction of the dumped waste, and the measured compaction parameters (γd and wopt) from the “old” sites at Udapalatha and Hambantota were higher compared to “new” sites. The waste composition also greatly affected the compaction, and the measured γd and wopt from the Karadiyana site were relatively low, even though the sample age was >20 years after the waste was dumped; this was probably due to the higher amounts of the hardly compacted materials, such as “Plastic” and “Glass and wood”, compared to the other samples. In the results of the direct shear tests, both strain hardening and softening were observed in the tested waste samples in this study, depending on the difference in vertical stress. In addition, both volume expansion and reduction were observed in the tested waste samples, depending on the difference in waste composition. Based on the Pearson correlations among the measured physicochemical parameters and the mechanical parameters, the LOI was a good indicator for quickly assessing the mechanical parameters of the “fresh” and “old” waste materials in this study, due to the insignificant sensitivity of the waste age and the climate condition in Sri Lanka.
Due to the inherent heterogeneity of dumped MSW and its composition, the different climate and geographical conditions of dumping sites, biodegradability with age, and the management system of dumping sites, the physicochemical and mechanical properties of dumped MSW vary widely among tested samples. Additionally, the size and shape (i.e., scale effect) and the pretreatments (e.g., sieving and moisture control) of the tested specimens affect the measured data on the mechanical properties in the laboratory. In addition, the physicochemical and mechanical properties of dumped MSW (e.g., in situ density, shear strength, cohesion, and so on) should be examined not only through laboratory testing but also through actual field experiments, in order to produce adequate evaluations of mechanical behavior and the long-term performance of MSW dumping sites, and to propose a suitable rehabilitation technique to avoid the slope failure and landslide of uncontrolled MSW dumping sites in developing countries. Further studies are needed to understand the physicochemical and mechanical properties of dumped MSW, which can be achieved by increasing more laboratory and in situ testing samples and examining the factors that affect the testing results. As shown in this study, however, there is a possibility that several key mechanical properties of dumped waste can be correlated with an easy measurable indicator (i.e., LOI) and this approach would be effective to assess and characterize the mechanical properties of dumped waste that has an inherent heterogeneity.

Author Contributions

Conceptualization, K.K., N.H.P., A.M.N.A. and L.C.K.; methodology, A.B.K.T.P., N.H.P., A.M.N.A., L.C.K. and K.K.; formal analysis, M.R.I., A.B.K.T.P. and K.K.; investigation, resources, and data collection, A.B.K.T.P., M.R.I. and K.K.; writing—original draft preparation, A.B.K.T.P., M.R.I. and K.K.; writing—review and editing, K.K., N.H.P., A.M.N.A. and L.C.K.; visualization, A.B.K.T.P., M.R.I. and K.K.; supervision, K.K.; project administration, K.K., N.H.P., A.M.N.A. and L.C.K.; funding acquisition, K.K. All authors have read and agreed to the published version of the manuscript.

Funding

This research was supported by the JST–JICA Science and Technology Research Partnership for the Sustainable Development Program (SATREPS) project (No. JPMJSA1701).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The data presented in this study are available on request from the corresponding author. The data are not publicly available due to the information security conditions of the project.

Acknowledgments

We acknowledge Nalin Mannapperuma at the Waste Management Authority of Sri Lanka, for supporting the field sampling at the Karadiyana waste landfill site. We thank H. Ohata, and B.L.C.B. Balasooriya, former master students, for their dedicated effort on fieldwork and laboratory tests.

Conflicts of Interest

The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.

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Figure 1. Sampling locations of tested materials: (a) Karadiyana, (b) Udapalatha, and (c) Hambantota MSW dumping sites. Information of sampling sites is also given (map data © 2022 Google).
Figure 1. Sampling locations of tested materials: (a) Karadiyana, (b) Udapalatha, and (c) Hambantota MSW dumping sites. Information of sampling sites is also given (map data © 2022 Google).
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Figure 2. Sorted waste materials taken from the Karadiyana site.
Figure 2. Sorted waste materials taken from the Karadiyana site.
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Figure 3. (a) Direct shear test apparatus and (b) tested sample of the Karadiyana site (<9.5 mm).
Figure 3. (a) Direct shear test apparatus and (b) tested sample of the Karadiyana site (<9.5 mm).
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Figure 4. Particle size distributions (PSD) of the tested samples.
Figure 4. Particle size distributions (PSD) of the tested samples.
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Figure 5. Depth profiles of physical and chemical properties at waste dumping sites. Closed circles represent “Old” and open circles represent “New”.
Figure 5. Depth profiles of physical and chemical properties at waste dumping sites. Closed circles represent “Old” and open circles represent “New”.
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Figure 6. Compaction curves of (a) waste samples and (b) subsoil samples.
Figure 6. Compaction curves of (a) waste samples and (b) subsoil samples.
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Figure 7. Shear stress (τ) and vertical displacement (εv) as a function of shear displacement (SD) for (a,b) Karadiyana old, (c,d) Udapalatha new, (e,f) Udapalatha old, (g,h) Hambantota new, and (i,j) Hambantota old.
Figure 7. Shear stress (τ) and vertical displacement (εv) as a function of shear displacement (SD) for (a,b) Karadiyana old, (c,d) Udapalatha new, (e,f) Udapalatha old, (g,h) Hambantota new, and (i,j) Hambantota old.
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Figure 8. Comparison of measured shear strength (τ) at SD = 15 mm to the reported range of the τ–σv relationship in previous studies [50,51].
Figure 8. Comparison of measured shear strength (τ) at SD = 15 mm to the reported range of the τ–σv relationship in previous studies [50,51].
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Figure 9. Relationships between LOI and (a) GS, (b) γdmax, (c) wopt, (d) c, and (e) ϕ. Linear regression lines are given as solid lines, and 95% confidence intervals are given as broken lines [25,46].
Figure 9. Relationships between LOI and (a) GS, (b) γdmax, (c) wopt, (d) c, and (e) ϕ. Linear regression lines are given as solid lines, and 95% confidence intervals are given as broken lines [25,46].
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Table
Table 1. Physical and chemical properties of tested samples. Literature data from Sri Lankan dumping sites [42] are also given.
Table 1. Physical and chemical properties of tested samples. Literature data from Sri Lankan dumping sites [42] are also given.
Sample LocationAgeDepthDescriptionwfγd, In-situAtterberg LimitsGspHECLOI
(Year)(m)(%)(kN m−3)wL (%)wP (%)IP(mS cm−1)(%)
Karadiyana site
Old>200.0–2.0Blackish dumped waste45.5----2.267.11.4619.5
2.0–4.059.0----2.267.31.6318.7
4.0–6.047.8----2.357.31.4113.6
6.0–8.065.94.6868.254.313.92.667.51.5511.2
Original soil-2.0–3.0Peaty soil1375.0454.236.118.12.426.55.3720.9
Udapalatha site
New<30.0–1.0Blackish dumped waste with fine sand60.26.41NM *NM *NP **1.966.92.2423.1
1.0–2.0Blackish dumped waste with clay and sand77.77.03NM *NM *NP **1.817.21.8331.6
2.0–2.75Blackish dumped waste with fine sand119-NM *NM *NP **1.696.92.3624.0
Old7–110.0–1.0Black, dumped waste83.85.31NM *NM *NP **1.996.80.8824.4
1.0–2.01035.17NM *NM *NP **2.127.40.4721.7
2.0–3.0934.56NM *NM *NP **2.17.11.2623.6
Subsoil-1.0–2.0Brown, medium to fine sand with gravel12----2.5460.042.07
Hambantota site
New<10.5–1.0Blackish dumped waste with clay and sand61.97.825.7NM *-2.527.60.69.96
Old (pit 1)7–80.0–0.5Blackish dumped waste with clay and sand17.810.4---2.647.30.2367.10
0.5–1.036.210.3---2.727.30.3087.44
Old (pit 2)0.0–0.524.112.129.5NM *-2.668.20.485.78
0.5–1.019.98.4530.615.515.12.768.30.385.50
Subsoil-1.0–2.0Gray, weathered silty sandy clay18.6-24.822.91.892.677.50.073.44
Karadiyana [42]11–2---61.736.824.91.73--72–80
21–2---50.336.015.61.66--
7–101–3---20.415.94.51.84--35–44
Jaffna [42]10–13---18.516.12.42.08--18–23
13–15---20.515.54.02.24--
NM *: Not measurable, NP **: Non-plastic.
Table
Table 2. Waste compositions of tested samples.
Table 2. Waste compositions of tested samples.
MaterialKaradiyana OldUdapalatha NewUdapalatha OldHambantota NewHambantota Old
Paper0.60.11.70.00.0
Plastic5.43.22.30.00.0
Vinyl5.27.76.83.68.8
Glass, ceramic, and metal4.06.75.93.33.4
Leather and rubber1.40.12.80.00.0
Textile1.91.04.61.10.4
Grass and wood13.810.86.50.64.5
Cementitious material3.013.44.20.00.0
Gravel (>9.50 mm)8.35.79.017.58.2
Residues (2.0–4.75 mm)33.217.121.631.530.7
Residues (<2.0 mm)22.934.334.642.444.0
Others0.40.00.00.00.0
Total100100100100100
Table
Table 3. Summary of compaction and shear parameters of tested samples. Literature data from [42] and others are also given.
Table 3. Summary of compaction and shear parameters of tested samples. Literature data from [42] and others are also given.
Sample Details
(Age after Dumping)		DepthCompactionDirect Shear StressShear Strength Parameters *Measured SD Range (%)Reference
(m)wopt
(%)		γdmax
(kN m−3)		τ (kN m−2)c
(kN m−2)		ϕ
(o)
σv = 25 kPaσv = 50 kPaσv = 75 kPa
Karadiyana site
Old (>20 years)6.0–8.039.310.853.774.898.1354815This study
Original soil2.0–3.062.19.3-----
Udapalatha site
New (<3 years)0.0–1.039.710.934.953.963.32031
1.0–2.033.710.545.470.478.22638
2.0–2.7548.69.745.456.872.73030
Old (7–11 years)0.0–1.039.010.823.854.563.72329
1.0–2.039.911.145.358.988.41344
2.0–3.036.211.338.654.469.82432
Subsoil1.0–2.011.019.3-----
Hambantota site
New (<1 year)0.5–1.020.514.137.663.577.22435
Old (pit 1) (7–11 years)0.0–0.513.417.3-----
0.5–1.016.116.3-----
Old (pit 2) (7–11 years)0.0–0.515.416.838.059.288.111.745.1
0.5–1.017.016.852.473.994.731.340.3
Subsoil1.0–2.016.618.3-----
The literature
(Sri Lanka: Wet climate zone)
Karadiyana (<1 year)1–2469.60---10.55615[42]
Karadiyana (<2 years)1–2479.15---15.149.515
(Sri Lanka: Dry climate zone)
Jaffna (7–10 years)1–320.315.2---27.62815
Jaffna (10–13 years)1–316.715.6---34.041.515[42]
Jaffna (13–15 years)1–316.515.4---17.74415
(Other regions)
Fresh Landfill-704.1018024056031–6426–3015[13]
Landfills (<1 years)-6710.01356117232415[46]
Landfill (<2 years)--11–17---9–1420–2910[47]
Landfill (12–34 years)--12.6–15.8---14365[9]
Landfill (2–25 years)1–939–52.35.1–10.1501002504.4–13.722–3015[48]
NA *: Not available.
Table
Table 4. Pearson correlation matrix for the measured physicochemical and mechanical parameters. Values >|0.80| are given in bold.
Table 4. Pearson correlation matrix for the measured physicochemical and mechanical parameters. Values >|0.80| are given in bold.
ParametersGsLOI (%)pHEC
(mS cm−1)		γdmax
(kN m−3)		wopt (%)c
(kN m−2)		ϕ
(o)		No. of Samples
Gs1−0.890.64−0.700.70−0.68−0.470.9117
LOI 1−0.680.61−0.860.800.58−0.7620
pH 1−0.510.71−0.69−0.180.8920
EC 1−0.780.780.45−0.8520
γd, max 1−0.97−0.310.8112
wopt 10.30−0.7912
c 1−0.469
ϕ 19
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Iqbal, M.R.; Piumali, A.B.K.T.; Priyankara, N.H.; Alagiyawanna, A.M.N.; Kurukulasuriya, L.C.; Kawamoto, K. Characterization of Physicochemical and Mechanical Properties of Dumped Municipal Solid Waste in Sri Lanka as Affected by the Climate Zone and Dumping Age. Sustainability 2022, 14, 4706. https://doi.org/10.3390/su14084706

AMA Style

Iqbal MR, Piumali ABKT, Priyankara NH, Alagiyawanna AMN, Kurukulasuriya LC, Kawamoto K. Characterization of Physicochemical and Mechanical Properties of Dumped Municipal Solid Waste in Sri Lanka as Affected by the Climate Zone and Dumping Age. Sustainability. 2022; 14(8):4706. https://doi.org/10.3390/su14084706

Chicago/Turabian Style

Iqbal, Muhammad Rashid, Abeywickrama Bamunusin Kankanamge Thilini Piumali, Nadeej Hansaraj Priyankara, Alagiyawanna Mohottalalage Nayana Alagiyawanna, Laksiri Chandana Kurukulasuriya, and Ken Kawamoto. 2022. "Characterization of Physicochemical and Mechanical Properties of Dumped Municipal Solid Waste in Sri Lanka as Affected by the Climate Zone and Dumping Age" Sustainability 14, no. 8: 4706. https://doi.org/10.3390/su14084706

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